Stevenson Creek Watershed Management Plan 

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EXECUTIVE SUMMARY 

Watershed Description

The Stevenson Creek Watershed, the largest and most urbanized watershed within 

the City of Clearwater, drains 6,286 acres in west central Pinellas County. Of this area, 

4,057 acres (65 percent) are within the Clearwater city limits. The remaining 35 percent 

of the basin is within the City of Dunedin (1,287 acres or 20%), unincorporated Pinellas 

County (859 acres or 14%) and the City of Largo (83 acres or about 1%). 

Stevenson Creek discharges to Clearwater Harbor. The majority of the creek has 

been channelized or otherwise altered, and little of the historic floodplain remains intact. 

Land uses within the basin are predominantly medium- and high-density residential, 

commercial, and open space. Approximately 90 percent of the watershed has been 

developed, and the vast majority of the development occurred prior to the implementation 

of regulatory requirements for floodplain preservation, environmental protection, 

stormwater treatment and attenuation. Several developments have been constructed 

within the creek’s floodplain and have experienced severe flooding. In addition, the 

creek and its tributaries experience moderate to severe erosion problems due to steep 

embankments, improper maintenance, highly erodable soils, and inadequate right-of-way. 

The majority of the land use changes within the watershed have been detrimental to 

water quality, flood protection, and wildlife habitat. Urban development has resulted in 

greater stormwater runoff volumes and peak flow rates, as well as the transport of 

sediments and pollutants into the creek. 

Purpose and Objectives

The Stevenson Creek Watershed Management Plan has been initiated as the result of 

a cooperative agreement between the City of Clearwater and the Southwest Florida Water 

Management District (SWFWMD). Stormwater quality and quantity are identified 

within the City of Clearwater Comprehensive Plan as areas of service deficiencies which 

must be addressed. 
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The basic purpose of the management plan is to identify the causes and sources of 

problems such as flooding, water quality degradation, excessive channel erosion, and loss 

of riparian habitat. Once these problems were identified, recommendations were made to 

solve or alleviate the problems. Recommendations include capital improvement projects 

(i.e. stormwater infrastructure improvements), creation and restoration of habitat, 

maintenance strategies, pollution reduction programs, and public involvement and 

awareness. This management plan will be used as a tool in the planning, regulation, and 

management of natural resources and future development, and as a basis for determining 

and prioritizing capital improvements by the City of Clearwater and SWFWMD. 

Data Collection

The information-gathering process included such activities as a literature search and 

review of existing data, field reconnaissance and ground-truthing of aerial photography, 

ground surveying, streamflow monitoring, surface water sampling and testing, habitat 

assessment, interviews with City operations personnel, and input from residents of the 

watershed. 

Flood Protection Level of Service

In order to assess the current flood protection level of service and to determine the 

most effective means of alleviating the identified flooding problems, a hydrologic and 

hydraulic model of the watershed was prepared. 

The Advanced Interconnected Channel and Pond Routing Model, Version 2.2 

(AdICPR) was chosen for the hydrologic and hydraulic modeling analysis. To provide 

the necessary level of detail, the basin was divided into a total of 307 discrete subbasins 

averaging 20.5 acres in size. The delineation of subbasins was dictated to a large extent 

by the complexity of the drainage network itself and the need to define the contributing 

drainage area to modeled elements of the conveyance system. 

The AdICPR model was calibrated to measured rainfall and streamflow data 

collected for this project. The large storm of July 15, 2000 was used as the calibration 

event. Once calibrated, the model was used to simulate the 5, 10, 25, 50, 100, and 500-

year design flood events. Floodplain mapping and flood profiles were prepared in order 
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to identify flooding problem areas. This information will be used to support a request for 

revision of the applicable FEMA flood insurance rate maps. 

Design 100 year flood elevations were compared with surveyed finished floor 

elevations of homes and businesses within the 100-year floodplain. Of the 470 structures 

entered into the database, 263 structures were found to have finished floor elevations 

below the 100-year flood level. This is, by definition, a structure flooding level of 

service deficiency. The majority of these structures are located within the primary 

floodplains of the Stevenson Creek and Spring Branch main channels. However, many 

of the identified FPLOS deficiencies result from inadequate secondary drainage systems 

that feed into the main channels. 

Natural Systems

The entire watershed was investigated for undeveloped land, wetlands, natural areas, 

and potential restoration or preservation areas. The boundaries of the natural areas were 

identified and mapped on aerial photography. These areas were characterized using the 

Florida Land Use Cover and Forms Classification System (FLUCCS) (FDOT, 1985). 

The Stevenson Creek Watershed is a highly urbanized, densely populated area with 

little to offer in the way of natural systems. With one exception, the only undeveloped 

areas are golf courses and city parks. Wetlands are predominantly small isolated 

stormwater retention ponds or natural lakes that have been altered to such a degree that 

their origin can only be determined from historic aerial photography. The waterways are 

predominantly channelized with little riparian habitat. The intense development has also 

altered the estuarine system so that little habitat is provided at the mouth of Stevenson 

Creek. 

Water Quality Assessment

Low dissolved oxygen levels, fecal contamination, and excessive nutrient 

concentrations are the primary water quality issues that have been identified in the 

watershed, and as such, water quality in Stevenson Creek is rated as “poor” by the state. 

The state’s rating is based on sampling conducted by the Pinellas County Department of 
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Environmental Management (PDEM). The city’s ambient monitoring program as well as 

monitoring conducted for this study affirms these water quality issues. 

Stevenson Creek is included on Florida’s impaired waters list {303(d) List} due to 

concerns over dissolved oxygen, fecal coliform bacteria, and nutrients. The FDEP has 

given Stevenson Creek a priority rating of “High”. Stevenson Creek is located in the 

“Crystal River to St. Petersburg Beach Basin” which is in Group 5 of the basin rotation 

cycle. TMDL development activity is expected to begin in 2004. 

Water quality assessments conducted for this study included the following elements: 

• Review of Existing Data, 

• Base flow and storm event monitoring program, 

• Water quality data interpretation, 

• Nonpoint source loading assessment, and

• Fecal contamination source tracking study.

Capital Improvement Projects

The relative scarcity of publicly-owned and vacant land within the watershed limited 

the range of available alternatives and posed a unique challenge in meeting all the goals 

of the Watershed Management Plan in a cost effective manner. For this reason, 

acquisition of private property, including 33 flood-prone or flood-susceptible singlefamily residential homes, is recommended in order to provide the necessary land for 

various infrastructure improvement projects that will benefit the watershed as a whole. 

In most, but not all cases, it was considered feasible and cost-effective to achieve the 

adopted flood protection level of service goals. A total of 26 individual capital projects 

are recommended, consisting of a combination new stormwater management facilities 

and retrofits to existing facilities and infrastructure. If all recommended projects are 

implemented, 243 of the identified 334 structure FPLOS deficiencies (73%) will be 

remedied. Many (28) of the remaining FPLOS deficiencies are located within the coastal 

high hazard area of Lower Stevenson Creek and are susceptible to flooding from storm 

surge. Reductions in the riverine floodplain (flooding due to rainfall and runoff) will 

therefore not remedy these FPLOS deficiencies. The combined projects would remove 
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FPLOS deficiencies at 33 locations on residential streets, 16 locations on collector roads, 

and on one arterial road. 

Water quality, habitat, erosion and sedimentation projects were developed 

individually and in conjunction with the recommended flood protection projects wherever 

feasible. Alternative projects were evaluated with respect to water quality improvement 

benefits. 

Other Improvements/Recommendations

In addition to the capital improvement projects, the WMP includes recommendations 

for watershed maintenance activities, exotic plant eradication, public education and 

involvement, and legal and regulatory framework. A more detailed and comprehensive 

study to pinpoint the source(s) of the fecal coliform bacteria is also recommended. The 

study would serve as the basis for developing an effective strategy to address the fecal 

contamination problem. 

Capital Costs

For purposes of budgetary planning, cost estimates were made of each recommended 

capital improvement project. The cost estimates are based on the conceptual design and 

are subject to change pending completion of a more detailed design process. The total 

estimated cost of the recommended projects is approximately $27 million, in 2001 

dollars, including property acquisition design, and permitting. The magnitude and scope 

of the recommended improvements, coupled with budgetary constraints, will require 

phased implementation of the plan over a number of years. 

Project Prioritization

Capital projects that can be expected to provide the greatest overall benefit in the 

most cost effective manner were identified using a project ranking procedure. This 

management tool is a convenient and effective method of recommending priorities for the 

allocation of available funding. To help identify the priority projects in the Stevenson 

Creek Watershed Management Plan, a set of comparative evaluation criteria were 

identified, and a project ranking matrix was developed. Within each category, individual 

projects were graded on a scale from 0 to 10, with the lowest score indicating no real 
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benefit and the highest indicating a high beneficial value. The categories considered in 

the ranking analysis included the following: 

• flood control benefits, 

• water quality benefits, 

• ecological benefits, 

• channel erosion and sedimentation control benefits, 

• Recreational and Educational Benefits, 

• Implementability, and 

• Relative Benefits to Cost. 

Those projects which serve multiple purposes rank the highest when compared to 

those with singular objectives. Also apparent is the observation that the projects that rank 

the highest generally have the highest scores in the relative benefits to cost category. 

Through the public meetings, workshops, and meetings among members of the 

project team, five projects were identified as potentially controversial. These include the 

highest-ranked project, the Glen Oaks stormwater detention facility. Winning public 

support for these projects through the City’s public information initiatives will be crucial 

to successful implementation of these projects. The final design and implementation of 

these projects must be sensitive to resident’s potential concerns regarding alternative 

recreational opportunities, the environment, safety, aesthetics, and property values.
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TABLE OF CONTENTS 

STEVENSON CREEK WATERSHED MANAGEMENT PLAN 

FINAL REPORT 

SECTION Page 

SECTION 1.0 INTRODUCTION............................................................................................... 1.1-1 

1.1 What is a Watershed Management Plan? ................................................. 1.1-1 

1.2 The Benefits of a Watershed Management Approach.............................. 1.1-2 

1.3 The Stevenson Creek Watershed .............................................................. 1.1-2 

1.3.1 Watershed Location and Description ......................................... 1.1-2 

1.3.2 Basin History.............................................................................. 1.1-4 

1.4 Project Objectives..................................................................................... 1.1-6 

SECTION 2.0 EXISTING CONDITIONS ANALYSIS AND PROBLEM 

IDENTIFICATION ............................................................................................. 2.1-1 

2.1 Flooding Conditions Assessment and Problem Identification.................. 2.1-1 

2.1.1 Watershed Model Selection ....................................................... 2.1-1 

2.1.2 Hydrologic Model Development................................................ 2.1-2 

2.1.2.1 Subbasin Delineations ................................................ 2.1-3 

2.1.2.2 Land Use..................................................................... 2.1-5 

2.1.2.3 Impervious Areas........................................................ 2.1-9 

2.1.2.4 Runoff Curve Number ................................................ 2.1-9 

2.1.2.5 Time of Concentration.............................................. 2.1-15 

2.1.3 Hydraulic Model Development ................................................ 2.1-15 

2.1.3.1 Drainage Facility Inventory ...................................... 2.1-16 

2.1.3.2 Channel Cross-Section and Floodplain 

Definition.................................................................. 2.1-20 

2.1.3.3 Storage Node Stage-Area Relationships................... 2.1-21 

2.1.3.4 Model Schematic ...................................................... 2.1-22 

2.1.3.5 Boundary Conditions ................................................ 2.1-24 

2.1.4 Model Calibration and Verification ......................................... 2.1-25 

2.1.4.1 Introduction............................................................... 2.1-25 

2.1.4.2 Streamflow and Precipitation Gaging Data .............. 2.1-25 

2.1.4.3 Selection of Calibration/Verification 

Storm Events............................................................. 2.1-27 

2.1.4.4 Calibration Parameters and Results.......................... 2.1-29 
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TABLE OF CONTENTS (CONTINUED) 

SECTION Page 

2.1.5 Flooding Conditions Assessment ............................................. 2.1-37 

2.1.5.1 Design Storm Events................................................. 2.1-39 

2.1.5.2 Existing Flooding Conditions ................................... 2.1-39 

2.1.5.3 Flooding Level of Service Criteria ........................... 2.1-41 

2.1.5.4 Flooding Problem Identification............................... 2.1-43 

2.2 Natural Resources Assessment and Problem Identification ..................... 2.2-1 

2.2.1 Introduction ................................................................................ 2.2-1 

2.2.2 Existing Conditions .................................................................... 2.2-2 

2.2.3 Wildlife..................................................................................... 2.2-12 

2.2.4 Endangered and Threatened Species........................................ 2.2-12 

2.3 Water Quality Assessment and Problem Identification............................ 2.3-1 

2.3.1 Existing Data .............................................................................. 2.3-2 

2.3.1.1 Existing Monitoring Programs.................................... 2.3-4 

2.3.1.2 Other Existing Data .................................................... 2.3-6 

2.3.2 Monitoring Program ................................................................... 2.3-9 

2.3.2.1 Monitored Basins........................................................ 2.3-9 

2.3.2.2 Hydrologic Monitoring............................................. 2.3-10 

 2.3.2.2.1 Water Quality .................................... 2.3-17 

2.3.3 Water Quality Characteristics .................................................. 2.3-17 

2.3.3.1 Petroleum Hydrocarbons .......................................... 2.3-24 

2.3.3.2 Oxygen Demand ....................................................... 2.3-25 

2.3.3.3 Solids ........................................................................ 2.3-28 

2.3.3.4 Metals ....................................................................... 2.3-28 

2.3.3.5 Nutrients ................................................................... 2.3-33 

2.3.3.6 Bacteria ..................................................................... 2.3-34 

2.3.4 Nonpoint Source Loading......................................................... 2.3-34 

 2.3.4.1 Runoff Coefficients.................................................. 2.3-37 

 2.3.4.2 Event Mean Concentrations ..................................... 2.3-40 

 2.3.4.2.1 In-Stream EMCs................................ 2.3-40 

 2.3.4.2.2 Exisitng Stormwater Runoff 

 Treatment .......................................... 2.3-41 

 2.3.4.2.3 Landuse-Based EMCs ....................... 2.3-43 

 2.3.4.3 Results...................................................................... 2.3-46 

SECTION 3.0 RECOMMENDED MASTER PLAN IMPROVEMENTS ................................... 3.1-1 

3.1 Flood Protection, Water Quality, Habitat, Erosion and 

Sedimentation Improvements ................................................................... 3.1-1 

3.1.1 Subwatershed 1: Spring Branch ................................................. 3.1-5 
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TABLE OF CONTENTS (CONTINUED) 

SECTION Page 

3.1.2 Subwatershed 2: Lower Stevenson Creek ................................ 3.1-22 

3.1.3 Subwatershed 3: Middle Stevenson Creek............................... 3.1-30 

3.1.4 Subwatershed 4: Upper Stevenson Creek................................. 3.1-35 

3.1.5 Subwatershed 5: Hammond Branch ......................................... 3.1-43 

3.1.6 Subwatershed 6: Lake Bellevue Branch................................... 3.1-52 

3.1.7 Subwatershed 7: Jeffords Street Branch................................... 3.1-58 

3.2 Human-Sourced Fecal Contamination Study............................................ 3.2-1 

3.2.1 Purpose of Further Study............................................................ 3.2-1 

3.2.2 Plan of Study .............................................................................. 3.2-2 

3.2.3 Dissemination of Results to End Users ...................................... 3.2-3 

3.3 Recommended Watershed Maintenance Plan........................................... 3.3-1 

3.4 Public Awareness and Involvement Programs.......................................... 3.4-1 

3.4.1 Adopt-a-Creek Program for Stevenson Creek............................ 3.4-1 

3.4.2 Proper Use of Pesticides and Fertilizers..................................... 3.4-2 

 3.4.2.1 Pesticide Use........................................................... 3.4-2 

 3.4.2.2 Fertilizers ................................................................ 3.4-3 

3.4.3 “Green” Thumb Landscaping Practices ..................................... 3.4-3 

3.4.4 Florida Yards and Neighborhoods Program............................... 3.4-4 

3.4.5 Storm Drain Marking Program................................................... 3.4-5 

3.5 Exotic Plant Eradication Program ............................................................ 3.5-1 

3.5.1 Brazilian Pepper ......................................................................... 3.5-2 

3.5.2 Australian pine ........................................................................... 3.5-3 

3.5.3 Melaleuca ................................................................................... 3.5-3 

3.5.4 Other Exotics.............................................................................. 3.5-4 

3.5.5 Estuary Restoration Plan ............................................................ 3.5-4 

3.5.6 Summary and Recommendations ............................................... 3.5-5 

3.6 Legal and Regulatory Framework ............................................................ 3.6-1 

3.6.1 U.S. Army Corps of Engineers................................................... 3.6-1 

3.6.2 U.S. Environmental Protection Agency ..................................... 3.6-2 

3.6.3 Federal Emergency Management Agency .................................. 3.6-2 

3.6.4 Southwest Florida Water Management District 

Florida Department of Environmental Protection...................... 3.6-4 

3.6.5 City of Clearwater....................................................................... 3.6-4 

3.7 Capital Improvement Cost Estimates........................................................ 3.7-1 
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TABLE OF CONTENTS (CONTINUED) 

SECTION Page 

SECTION 4.0 WATERSHED MANAGEMENT PLAN PROJECT 

 PRIORITIZATION............................................................................................... 4.1-1 

SECTION 5.0 REFERENCES AND BIBLIOGRAPHY .............................................................. 5.1-1 

5.1 Drainage, Hydrology, and Flood Protection............................................. 5.1-1 

5.2 Water and Sediment Quality..................................................................... 5.1-3 

5.3 Natural Resources..................................................................................... 5.1-4 
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LIST OF TABLES 

Table 2.1-1 Node and Subbasin Numbering Scheme 

Table 2.1-2 Basin Land Use Percentages 

Table 2.1-3 Hydrologic Soil Group Acreages and Percentages 

Table 2.1-4 Runoff Curve Number Computation Matrix 

Table 2.1-5 Comparison of Measured and Simulated High Water Elevations 

Table 2.1.6 Comparison of Simulated 100-Year Peak Flows and Flood Stages 

Table 2.1-7 Proposed Flood Control Level of Service Criteria for Stevenson Creek 

Table 2.1-8 Summary of Structure Flood Protection Level of Service Deficiencies 

Table 2.2-1 Land Use Classification by Major Subbasin 

Table 2.2-2 Wildlife Observed or Expected Within the Stevenson Creek Watershed 

Table 2.2-3 Endangered, Threatened, or Special Concern Species Present or 

Potentially Present in the Stevenson Creek Watershed 

Table 2.3-1 Loads During Monitoring Period 

Table 2.3-2 Water Quality Sampling Parameters 

Table 2.3-3 Overall Hydrologic Conditions at Monitoring Stations 

Table 2.3-4 Laboratory Results 

Table 2.3-5 Water Quality Indices 

Table 2.3-6 Base Flow Oxygen Demand 

Table 2.3-7 Storm Event Oxygen Demand 

Table 2.3-8 Base Flow Solids 

Table 2.3-9 Storm Event Solids 

Table 2.3-10 Metals 

Table 2.3-11 Base Flow Nutrients 

Table 2.3-12 Storm Event Nutrients 

Table 2.3-13 Runoff Coefficients 

Table 2.3-14 In-Stream EMCs 

Table 2.3-15 BMP Maximum Efficiencies 

Table 2.3-16 Landuse-Based EMCs 

Table 2.3-17 Landuse-Based EMCs – Selected Literature Value 

Table 2.3-18 Major Basin Loads 

Table 3.1-1 Maximum BMP Removal Efficiencies 

Table 3.1-2 Alternative Projects Water Quality Improvement Benefits

Table 3.1-3 Vegetation Recommended for Planting in Varying Water Depths

Table 3.3-1 Recommended Channel Maintenance Plan 

Table 3.5-1 Exotic Plant Species Within the Stevenson Creek Watershed 

Table 3.6-1 Proposed Flood Protection Level of Service (FPLOS) Criteria 

Table 3.7-1 Capital Improvement Project Cost Estimates

Table 4-1 Stevenson Creek Watershed Management Plan Improvement Project 

Ranking Matrix

Table 4-2 Project Precedence 
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LIST OF FIGURES 

Figure 1.3-1 Stevenson Creek Watershed Location Map

Figure 1.3.2 Stevenson Creek Bridge Near Clearwater, Fla, 1890 

Figure 2.1-1 Stevenson Creek Watershed Drainage Map and Model Schematic

Figure 2.1-2 Stevenson Creek Watershed Land Use Map

Figure 2.1-3 Stevenson Creek Watershed Hydrologic Soil Group Classification Map

Figure 2.1-4 AdICPR Node-Reach Schematic Existing Conditions

Figure 2.1-5 Locations of Monitoring Stations 

Figure 2.1-6 July 15, 2000 Storm Event

Figure 2.1-7 Box Culverts Downstream of Kings Highway Monitoring Station 

Figure 2.1-8 Vegetation in Channel Downstream of Drew Street Monitoring Station 

Figure 2.1-9 Rating Curve for Stevenson Creek at Drew Street

Figure 2.1-10 Rating Curve for Spring Branch at Kings Highway

Figure 2.1-11 Stevenson Creek July 15, 2000 Calibration Storm Comparison

Figure 2.1-12 Spring Branch July 15, 2000 Calibration Storm Comparison

Figure 2.1-13 Stevenson Creek June 12, 2000 Verification Storm Comparison

Figure 2.1-14 Spring Branch June 12, 2000 Verification Storm Comparison

Figure 2.1-15 Stevenson Creek Watershed Existing Conditions 100-and 500-Year 

Floodplain Map

Figure 2.1-16 Existing Conditions Flood Profiles Key Map

Figure 2.1-17 Stevenson Creek Flood Profile, Existing Conditions

Figure 2.1-18 Stevenson Creek Flood Profile, Existing Conditions

Figure 2.1-19 Stevenson Creek Flood Profile, Existing Conditions

Figure 2.1-20 Stevenson Creek Flood Profile, Existing Conditions

Figure 2.1-21 Stevenson Creek Flood Profile, Existing Conditions

Figure 2.1-22 Stevenson Creek Flood Profile, Existing Conditions

Figure 2.1-23 Spring Branch Flood Profile, Existing Conditions

Figure 2.1-24 Spring Branch Flood Profile, Existing Conditions

Figure 2.1-25 Flooding on Hillcrest Avenue, South of Lakeview Road 

Figure 2.3-1 Water Quality Monitoring Stations

Figure 2.3-2 Marshall Street WWTP Location 

Figure 2.3-3 Septic Tank Densities

Figure 2.3-4 Monitoring Stations Location and Coverage

Figure 2.3-5 Land Use by Monitoring Station 

Figure 2.3-6 Rainfall Conditions 

Figure 2.3-7 Stevenson Creek Hydrologic Record 

Figure 2.3-8 Stevenson Creek Hydrologic Record – Low Flow Detail 

Figure 2.3-9 Spring Branch Hydrologic Record 

Figure 2.3-10 Spring Branch Hydrologic Record – Low Flow Detail 

Figure 2.3-11 Existing Stormwater Treatment Areas

Figure 2.3-12 Existing Stormwater Treatment Coverage
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LIST OF FIGURES (CONTINUED) 

Figure 2.3-13 BOD Loading Rates by Subwatershed

Figure 2.3-14 TSS Loading Rates by Subwatershed

Figure 2.3-15 Nitrogen Loading Rates by Subwatershed

Figure 2.3-16 Phosphorus Loading Rates by Subwatershed

Figure 3.1-1 Improvement Projects Location Map

Figure 3.1-2 Private Crossing of Spring Branch Near Betty Lane, to be Removed 

Figure 3.1-3 Conceptual Plan of Project 1A.1

Figure 3.1-4 Conceptual Plan of Project 1A.2

Figure 3.1-5 Conceptual Plan of Project 1B

Figure 3.1-6 Conceptual Plan of Project 1C

Figure 3.1-7 Photograph of site of Project 1C 

Figure 3.1-8 Conceptual Plan of Project 1D 

Figure 3.1-9 Conceptual Plan of Project 1E

Figure 3.1-10 Conceptual Plan of Project 1F

Figure 3.1-11 Conceptual Plan of Project 1G

Figure 3.1-12 Conceptual Plan of Project 1H

Figure 3.1-13 Conceptual Plan of Project 2A

Figure 3.1-14 Conceptual Plan of Project 2B

Figure 3.1-15 Conceptual Plan of Project 2D

Figure 3.1-16 Photograph of site adjacent to Project 2D 

Figure 3.1-17 Conceptual Plan of Project 3A

Figure 3.1-18 Project 3A, Conceptual Plan Detail

Figure 3.1-19 Stevenson Creek Channel and Trees to Remain Along Hillcrest Avenue, 

Between Jeffords Street and Browning Street (Project 4A) 

Figure 3.1-20 Failing Retaining Wall Upstream of Browning Street to be Replaced and 

Vegetation to be Removed (Project 4A) 

Figure 3.1-21 Conceptual Plan of Project 4A

Figure 3.1-22 Conceptual Plan of Project 4B

Figure 3.1-23 Conceptual Plan of Project 4C

Figure 3.1-24 Conceptual Plan of Project 5A

Figure 3.1-25 Conceptual Plan of Project 5B

Figure 3.1-26 Conceptual Plan of Project 5C

Figure 3.1-27 Conceptual Plan of Project 5D

Figure 3.1-28 Conceptual Plan of Project 5E

Figure 3.1-29 Wetland Planting Illustration 

Figure 3.1-30 Conceptual Plan of Project 6A.1

Figure 3.1-31 Conceptual Plan of Project 6A.2

Figure 3.1-32 Conceptual Plan of Project 6B

Figure 3.1-33 Conceptual Plan of Project 7A

Figure 3.1-34 Conceptual Plan of Project 7B

Figure 3.1-35 Conceptual Plan of Project 7C
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LIST OF FIGURES (CONTINUED)

Figure 3.1-36 Project Conditions Flood Profiles Key Map

Figure 3.1-37 Stevenson Creek Flood Profile, Project Conditions

Figure 3.1-38 Stevenson Creek Flood Profile, Project Conditions

Figure 3.1-39 Stevenson Creek Flood Profile, Project Conditions

Figure 3.1-40 Stevenson Creek Flood Profile, Project Conditions

Figure 3.1-41 Stevenson Creek Flood Profile, Project Conditions

Figure 3.1-42 Stevenson Creek Flood Profile, Project Conditions

Figure 3.1-43 Spring Branch Flood Profile, Project Conditions

Figure 3.1-44 Spring Branch Flood Profile, Project Conditions

Figure 3.1-45 Project Conditions 100-Year Floodplain Comparison

Figure 3.6-1 Yard Waste on the Banks of Upper Stevenson Creek 
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TECHNICAL APPENDICES 

VOLUME I

APPENDIX A ADICPR HYDROLOGIC INPUT DATA SUMMARY 

APPENDIX B ADICPR HYDROLOGIC AND HYDRAULIC MODEL INPUT 

AND OUTPUT DATA FILES, CALIBRATION STORM EVENTS 

APPENDIX C ADICPR HYDROLOGIC AND HYDRAULIC MODEL INPUT 

AND OUTPUT DATA FILES, EXISTING CONDITIONS 

VOLUME II

APPENDIX D EXISTING CONDITIONS LEVEL OF SERVICE EVALUATION

APPENDIX E ADICPR HYDROLOGIC AND HYDRAULIC MODEL INPUT 

AND OUTPUT DATA FILES, PROPOSED CONDITIONS 

APPENDIX F PROPOSED CONDITIONS LEVEL OF SERVICE 

EVALUATION

VOLUME III

APPENDIX G URBAN HYDROLOGY FOR SMALL WATERSHEDS (TR-55) 

CHAPTERS 1-3 

APPENDIX H CAPITAL COST ESTIMATES

APPENDIX I WATER QUALITY MONITORING DATA 

APPENDIX J BACTERIAL SOURCE TRACKING STUDY

APPENDIX K POLLUTANT LOADING MODEL INPUT AND OUTPUT DATA

 

 Subbasin Loading – BOD

 Subbasin Loading – Nitrogen

 Subbasin Loading – TSS

 Subbasin Loading - Phosporus
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APPENDIX L PUBLIC MEETING QUESTIONNAIRES 
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SECTION 1.0 

INTRODUCTION 

1.1 WHAT IS A WATERSHED MANAGEMENT PLAN? 

Significant improvements in the protection and restoration of the physical, chemical, 

and biological integrity of the nation’s waters have been made in the last 25 years. The 

passage of the Clean Water Act and Safe Drinking Water Act has resulted in the control 

of pollution from “point sources” such as industrial waste and sewage treatment plants. 

However, until recently the federal laws have tended to focus on particular sources, 

pollutants, or water uses, and have not resulted in an integrated environmental 

management approach. Problems resulting from nonpoint pollution sources, habitat 

degradation, flooding, and wastewater overflows have not been resolved. These 

problems necessitate a comprehensive understanding of a complex system, and solutions 

that integrate disciplines and overlap political boundaries. This holistic, comprehensive 

approach is called a watershed management plan. The watershed management plan 

approach to improving the physical, chemical, and biological integrity of surface water is 

a three-part process. These three components include identifying the watershed’s natural 

boundaries, applying the latest scientific methods to identify problems, and coordinating 

the improvements within social, political, and economic constraints. 

• A watershed boundary incorporates all the land area that contributes stormwater 

runoff to a particular surface water body. 

• In order to identify, characterize, and evaluate the problems within a watershed, 

the latest scientific tools, techniques, and theory must be utilized. The proposed 

solutions must include the latest and most cost-effective methods of watershed 

rehabilitation, integrating various scientific disciplines and expertise. 

• Watersheds are seldom contained within a single political boundary. This 

necessitates a team approach, incorporating local, state, and federal agencies, as 
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well as the concerned public. Team members form a partnership and work 

together toward a common goal based on shared information, and an 

understanding of the priorities and responsibilities of all parties. 

1.2 THE BENEFITS OF A WATERSHED MANAGEMENT APPROACH 

Coordination of a watershed management plan is beneficial for environmental, 

financial, social, and administrative reasons. Managers from all levels of government 

will be better able to understand and reduce the cumulative effects of human activities in 

a watershed on pollution control, increased surface water runoff, fish and wildlife 

protection, drinking water protection, and other water resource programs when allowed to 

view the “big picture,” rather than just their portion of the watershed. The most critical 

problems are identified, and priorities can then be set to allocate the available financial 

and human resources. 

The watershed management approach also can result in significant savings by 

improving communication and coordination, which will in turn reduce costly duplication 

of efforts and conflicting actions. This cooperation gives an active voice in resource 

management to the people who depend on the area resources for their recreation, health, 

and overall quality of life. 

1.3 THE STEVENSON CREEK WATERSHED 

1.3.1 Watershed Location And Description 

The Stevenson Creek Watershed, the largest and most urbanized watershed within 

the City of Clearwater, drains 6,286 acres in west central Pinellas County (refer to Figure 

1.3-1). Of this area, 4,057 acres (65 percent) are within the Clearwater city limits. The 

remaining 35 percent of the basin is within the City of Dunedin (1,287 acres or 20%), 

unincorporated Pinellas County (859 acres or 14%) and the City of Largo (83 acres or 

about 1%). 
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(FIGURE 1.3-1) 
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Stevenson Creek discharges to Clearwater Harbor. The majority of the creek has 

been channelized or otherwise altered, and little of the historic floodplain remains intact. 

Land uses within the basin are predominantly medium- and high-density residential, 

commercial, and open space. Approximately 90 percent of the watershed has been 

developed, and the vast majority of the development occurred prior to the implementation 

of regulatory requirements for floodplain preservation, environmental protection, 

stormwater treatment and attenuation. Several developments have been constructed 

within the creek’s floodplain and have experienced severe flooding. In addition, the 

creek and its tributaries experience moderate to severe erosion problems due to steep 

embankments, improper maintenance, highly erodable soils, and inadequate right-of-way. 

1.3.2 Basin History 

Land use changes within the Stevenson Creek Watershed over the last 100 years have 

been significant. A cursory history of the changes within the basin can be determined 

from a review of historic archives and aerial photography. Aerial photography dated 

Figure 1.3-2 Stevenson Creek Bridge, near Clearwater, Fla., 1890.

(Photo courtesy of City of Clearwater Public Library) 
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1926 shows the Stevenson Creek Estuary to be much wider than it is now, approximately 

1,000’ wide at the mouth, compared to only 700’ today. Prior to 1926, the original 19th

Century wooden bridge connecting Clearwater to Dunedin, which spanned the entire 

estuary (Figure 1.3.2), was replaced with an earthen causway with a much narrower open 

span for Edgewater drive. The 1926 photography depicts a relatively intact floodplain 

and associated wetlands, with adjacent land uses predominantly agricultural, under 

development, or undeveloped. Some channelization had occurred within Spring Branch, 

and within Stevenson Creek between Drew Street and Druid Road. The east-west 

railroad that bisects the basin as well as the coastal railroad that borders the basin to the 

east had already been constructed. Most of the population at the time was concentrated 

within a 1⁄2-mile strip of land bordering Clearwater Harbor. Effects of the 1920’s land 

boom are evidenced by the numerous subdivision streets with sidewalks constructed 

throughout the interior portions of the watershed. However, by 1942, only a few homes 

had been built within these interior subdivisions. During the post-war boom of the 

1950’s and 1960’s, the majority of the watershed was built out within these medium 

density residential subdivisions and commercial developments. Also during this period, 

portions of the Stevenson Creek estuary were filled in along its southern banks. 

By 1974, over 95% of the developable area in the watershed had been developed or 

set aside as parks and golf courses, and the full length of Stevenson Creek and its 

tributaries had been channelized. Very little of the creek’s floodplain and associated 

wetlands remained intact. With the exception of the two golf courses bordering the creek, 

almost the entire floodplain of Stevenson Creek had been developed. 

The majority of the land use changes within the watershed have been detrimental to 

water quality, flood protection, and wildlife habitat. Urban development has resulted in 

greater stormwater runoff volumes and peak flow rates, as well as the transport of 

sediments and pollutants into the creek. The effects of land use changes within the 

watershed on wildlife habitat are described in Section 2.2. 
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In response to severe flooding experienced within the watershed as a result of a storm 

event in July of 1987, a flood control study was commissioned by the City of Clearwater 

in April of 1988. In the study, a three-phase flood control project was developed for the 

main channel of Stevenson Creek. To date, two of the three phases of the project have 

been constructed, consisting of the main channel segments between Betty Lane and 

Jeffords Streets. The third phase, which included segments upstream of Jeffords Street, 

has not been constructed, primarily because of environmental concerns. Because the 

objective of the original study was focused on flood control on the main stem of 

Stevenson Creek, water quality and environmental enhancement/ protection needs and 

problems were not addressed. The tributaries and secondary drainage systems were not 

analyzed in detail, and the Spring Branch portion of the watershed was excluded from the 

original study. 

1.4 PROJECT OBJECTIVES 

The Stevenson Creek Watershed Management Plan has been initiated as the result of 

a cooperative agreement between the City of Clearwater and the Southwest Florida Water 

Management District (SWFWMD). Drainage improvements for enhanced stormwater 

quality and quantity are identified within the City of Clearwater Comprehensive Plan as 

areas of service deficiencies which must be addressed. Section 16.2 of the Plan states: 

Objective – The City of Clearwater shall continue to develop watershed 

management plans which should seek to identify, evaluate, and implement 

the most cost effective and cost efficient programs for stormwater 

management, including stormwater quantity and quality... 

In addition to the municipal and regulatory involvement, the residents within the 

watershed have had an active role in the shaping of the watershed plan. Numerous 

suggestions and comments concerning management actions have been received from 

residents and other property owners in the area through documented reports and through 

the public meeting process. Public involvement is a very important component of this 
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plan; watershed improvements cannot be realized without the willingness and cooperation 

of residents within the watershed boundaries. 

The basic purpose of the management plan is to identify the causes and sources of 

problems such as flooding, water quality degradation, excessive channel erosion, and loss 

of riparian habitat. Once these problems were identified, recommendations were made to 

solve or alleviate the problems. Recommendations include capital improvement projects 

(i.e. stormwater infrastructure improvements), creation and restoration of habitat, 

maintenance strategies, pollution reduction programs, and public involvement and 

awareness. This management plan will be used as a tool in the planning, regulation, and 

management of natural resources and future development, and as a basis for determining 

and prioritizing capital improvements by the City of Clearwater and SWFWMD. The 

initial phase to meet this objective included a comprehensive analysis of the watershed in 

order to identify the problems to be addressed. 

The first task in the analysis process was to collect, record, and organize all 

potentially useful existing information relevant to the watershed. Once the data were 

collected and analyzed, any data deficiencies were noted and the missing data were 

gathered. The information-gathering process included such activities as a literature 

search and review of existing data, field reconaissance and ground-truthing of aerial 

photography, ground surveying, streamflow monitoring, surface water sampling and 

testing, habitat assessment, interviews with City operations personnel, and input from 

residents of the watershed. 

The second task included a comprehensive stormwater quantity and quality modeling 

analysis of the watershed. The model was used to develop a comprehensive watershed 

management plan with recommendations for site-specific physical improvements for 

flood protection, habitat improvement, and water quality improvement. This planning 

phase included a conceptual design sufficient to determine permit and construction 

feasibility, cost effectiveness, and property acquisition requirements. At the end of the 
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planning phase, meetings of the Management Plan participants will be held to discuss a 

course of action for proceeding to the implementation phase. 

 The following sections describe the methods used to gather the necessary data, how 

the data were applied in the development of the watershed plan, and the recommended 

improvements produced through the cooperative efforts of the project team. 
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SECTION 2.0 

WATERSHED ASSESSMENT AND PROBLEM IDENTIFICATION 

This section of the Watershed Management Plan describes the existing flooding, 

natural resources, and water quality conditions within the Stevenson Creek Watershed, 

and the watershed assessment methods used. The first portion of the section addresses 

the primary concern of those living within the watershed; the periodic flooding of roads 

and buildings. The second portion describes the natural resources available within the 

watershed, such as the location and quality of wildlife habitat. The third portion details 

the water quality assessment, including the results of the water quality sampling program 

and pollutant loading modeling. 

2.1 FLOODING CONDITIONS ASSESSMENT 

2.1.1 Watershed Model Selection 

This section details the methods and procedures used to perform the assessments of 

watershed hydrologic and hydraulic conditions. An important component of this 

Watershed Management Plan for Stevenson Creek is an assessment of the current flood 

protection level of service provided throughout the watershed. A thorough understanding 

of basinwide hydrologic and hydraulic processes is necessary to determine the most 

effective means of alleviating the identified flooding problems. The watershed model 

prepared for this Management Plan was used as a planning tool to assess the existing 

flooding problems and susequently, to optimize the flood protection benefits of the 

proposed improvements. 

The Advanced Interconnected Channel and Pond Routing Model, Version 2.2 

(AdICPR) was chosen for the hydrologic and hydraulic modeling analysis, in part because 

of its ability to mathematically represent the time-dependent processes that govern flow 

and stage in low-relief coastal watersheds such as Stevenson Creek. Furthermore, it was 
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necessary to select a model which has been accepted by the Federal Emergency 

Management Agency (FEMA) for flood insurance studies, since the results of the analysis 

will be used to support a request for revision of the applicable FEMA flood insurance rate 

maps. 

2.1.2 Hydrologic Model Development 

The hydrologic model used for this study is the SCS Runoff Curve Number (CN) and 

Unit Hydrograph Method contained within AdICPR. This method computes a runoff 

(flow) versus time relationship (hydrograph) for each subbasin, given a set of hydrologic 

input parameters. 

Hydrologic parameters required for the SCS Runoff CN and Unit Hydrograph 

Method include the following: 

• Subbasin drainage area 

• Subbasin time of concentration (TC) 

• Subbasin percent directly connected impervious area (DCIA) 

• Subbasin weighted runoff curve number (CN) for areas outside of DCIA 

• Unit hydrograph shape factor 

• Rainfall data 

A description of the methodologies used to derive each of these hydrologic 

parameters follows in the remainder of this section. 
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2.1.2.1 Subbasin Delineations 

The Stevenson Creek watershed drainage area consists of approximately 9.82 square 

miles (6,286 acres) of moderately sloping terrain in west central Pinellas County that 

discharges to Clearwater Harbor. To provide the level of detail that was deemed 

necessary to analyze the primary drainage facilities within the heavily urbanized 

Stevenson Creek watershed, the basin was divided into a total of 307 discrete subbasins 

that range in size from 1 to 197 acres. The average subbasin size is 20.5 acres. The 

delineation of individual subbasins was dictated to a large extent by the complexity of the 

drainage network itself and the need to define the contributing drainage area to modeled 

elements of the conveyance system. 

Approximately 20% and 14% of the watershed area lies within the City of Dunedin 

and unincorporated Pinellas County, respectively. Although these governmental bodies 

are not official participants in the Management Plan, approximately the same level of 

hydrologic and hydraulic model detail was applied in these areas. This was deemed 

necessary in order to accurately quantify the volumes and peak rates of runoff contributed 

to Stevenson Creek and its tributaries by these areas. 

Figure 2.1-1 in the attached map pocket shows the delineation of the Stevenson 

Creek watershed into its 307 individual subbasins. Subbasin ID numbers consist of the 

letter “B” followed by a four-digit number. The four-digit number generally coincides 

with the ID number of the node at the outlet of the subbasin. In cases where two 

subbasins drain to the same node, the second subbasin has an ID number equal to the 

node number plus one. Nodes and subbasins were generally numbered in order 

increasing in the upstream direction. For convenience, the 307 individual subbasins were 

aggregated into eight major subbasins, or “subwatersheds”. Subbasin and node numbers 

are grouped according to the subwatershed in which they lie, as follows: 
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Table 2.1-1 Node / Subbasin Numbering Scheme 

Subwatershed Node / Subbasin ID Range 

Lower Stevenson Creek 0000 – 0499 

Lower Spring Branch 0500 – 0999 

Upper Spring Branch 1000 – 1999 

Hammond Branch 2000 – 2999 

Middle Stevenson Creek 3000 – 3499 

Lake Belleview Branch 3500 – 3999 

Upper Stevenson Creek 4000 – 4139 

Jeffords Street Branch 4140 – 4999 

The means of defining subbasin boundaries employed a number of sources of 

information and methods. The principle source was 1”=200’ topographic aerial 

photographic mapping of the watershed provided by SWFWMD. This mapping shows 

overland topography, thus indicating direction of overland flow. However, because much 

of the watershed is developed, with a variety of residential, commercial, industrial, and 

institutional developments, man-made secondary drainage systems comprising swales, 

gutters, storm sewer systems, ditches, and detention ponds have interrupted the natural 

overland flow patterns within the basin and, in many cases, diverted storm runoff in 

directions that are not readily apparent from inspection of the topographic mapping. It is 

also important to note that the SWFWMD mapping within the basin is, for the most part, 

over 20 years old. Therefore, new development that has occurred within the watershed 

since that time does not appear on these maps, and drainage patterns and grades in certain 

areas have been altered since that time due to this new development. 

The City of Clearwater drainage atlas maps provided detailed layouts of the 

secondary drainage systems within the incorporated city portions of the watershed and 

proved to be of immense value for assisting in the delineation of the subbasins. In 

addition, record drawings of permitted stormwater management facilities within the basin 

on file with the SWFWMD were reviewed and referenced in the subbasin delineation 
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process as a means of defining the drainage systems and drainage areas for newer 

developments that did not show up on any of the previously listed information sources. 

The final check of subbasin delineations was field reconnaissance of the watershed to 

confirm the initial boundaries and to inspect the drainage facilities and conditions in the 

basin firsthand, to investigate areas where there was no information available from the 

previously listed sources, and to resolve discrepancies where there was a conflict between 

different sources of information regarding drainage facilities. 

2.1.2.2 Land Use 

Existing land use conditions within the Stevenson Creek watershed were defined 

with the aid of a Geographic Information System (GIS) land use coverage data file 

provided by SWFWMD. For convenience, the 26 different land use classifications that 

were defined in the SWFWMD land use coverage of the basin were consolidated into the 

following 13 categories: 

• Commercial 

• Cropland and Pastureland 

• Forest 

• Low Density Residential 

• Medium Density Residential 

• High Density Residential 

• Industrial 

• Institutional 

• Open Land and Range Land 

• Specialty Farms 

• Transportation, Communications and Utilities 

• Water 

• Wetlands 

For the purposes of this study, the medium density residential classification was 

redefined to include residential areas containing between 2 and 5 dwelling units per acre. 

In the SWFWMD classification system, this was considered to be high density. It was 

deemed necessary to reclassify these areas, because the actual (measured) impervious area 
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percentages in these areas are more consistent with literature values cited for medium 

density residential. The significance and determination of impervious area is described in 

the next section. This change increased the percentage of the basin classified as medium 

density residential from none to the majority of the basin. Areas of multi-family 

developments (i.e., apartment and condominium complexes) remained classified as high 

density residential. 

These land use coverages were then field-truthed by examination of recent aerial 

photography of the basin and comparing to the map to confirm that both the 

classifications and the areal extent are properly represented. Many adjustments were 

required. The majority involved the delineation of the developed portions of areas that 

were designated as institutional or transportation/utilities in the SWFWMD land use 

coverage to separate them from open land areas that occurred within these parcels to 

various degrees. The institutional land use classification includes parcels such as nursing 

homes, schools, churches, hospitals, auditoriums, and cemeteries, which can vary over a 

wide range in their degree of imperviousness. For the same reasons, significant open land 

areas within industrial and commercial tracts were delineated to segregate them from the 

actual developed portions of the parcels. Other changes were required in order to update 

the mapping to account for recent development. The resultant hydrologic land use 

classification map of the Stevenson Creek watershed that was used for model 

development purposes is shown in Figure 2.1-2. Table 2.1-2 presents a composite 

breakdown of land use acreages and percentages in the Stevenson Creek Watershed. 
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Table 2.1-2 Basin Land Use Percentages 

Land Use Classification Total Area

(acres) 

Percentage of Basin

(%) 

Commercial 610 9.7 

Cropland and Pastureland 5 0.1 

Forest 50 0.8 

Low Density Residential 56 0.9 

Medium Density Residential 3861 61.4 

High Density Residential 459 7.3 

Industrial 42 0.7 

Institutional 182 2.9 

Open Land and Range Land 573 9.1 

Specialty Farms 10 0.2 

Transportation, Communications, and Utilities 170 2.7 

Water 205 3.3 

Wetlands 63 1.0 

Total 6286 100.0 
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(Figure 2.1-2) 
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2.1.2.3 Impervious Areas 

Impervious areas are those surfaces such as rooftops and pavement, which impede 

the infiltration of runoff into the soil. Directly connected impervious area (DCIA) is 

defined as those impervious areas that are connected directly to the subbasin outfall (i.e., 

node) without flow occurring over a pervious surface. In the AdICPR model, DCIA is an 

optional parameter which, if used, is treated as a separate subarea within each subbasin. 

A separate hydrograph is computed for the DCIA, which is not subject to any initial 

abstraction (i.e., infiltration). Any impervious area which is not directly connected to the 

subbasin outfall is then used in computing a weighted curve number (CN) as described in 

the next section. 

For the Stevenson Creek watershed model, literature values of total percent 

imperviousness for the different land use classifications were utilized. Measurements of 

impervious coverage within representative samples of each land use classification were 

conducted using aerial photography, in order to confirm the literature values. The split 

between DCIA and non-directly connected impervious areas was determined through the 

model calibration process, as discussed in subsequent sections. 

2.1.2.4 Runoff Curve Number 

By superposition, the hydrograph computed using the DCIA is added by AdICPR to 

the hydrograph computed using a weighted runoff curve number (CN). This results in a 

single composite hydrograph, which is then input into the corresponding node of the 

hydraulic model. 

In the SCS method, the CN is a function of S, the potential maximum infiltration 

after runoff begins (in inches): 

CN = 1000

 S+10 

The standard SCS method uses the following empirical relationship: 

Ia = 0.2S 
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Where Ia is the initial abstraction, which includes all losses before runoff begins. It 

includes water intercepted by vegetation, shallow depression storage, evaporation, and 

infiltration. For design storm conditions in watersheds containing sandy soils, experience 

and literature on the subject indicate that infiltration losses comprise the majority of the 

initial abstraction. 

The weighted CN is therefore primarily a function of the non-directly connected 

impervious coverages (based on land use), and the infiltration capacity of the soils. For 

this study, a land use/ hydrologic soils group intersection analysis was performed using 

the ArcView/ArcInfo Geographic Information Systems (GIS) software. 

The Soil Conservation Service (SCS) (now the Natural Resources Conservation 

Service) of the U.S. Department of Agriculture has mapped soils in Pinellas County in its 

publication “Soil Survey of Pinellas County, Florida” (1972). This soil survey also 

provides generalized information on the hydrologic properties of the soil classifications. 

A standard method of soils classification is the hydrologic soils group. Soils are 

grouped into four hydrologic soil groups A through D. These groups are commonly used 

in hydrologic analyses to estimate infiltration rates and soil moisture capacities. 

Descriptions of these soil groups are: 

Hydrologic Soil Group A (low runoff potential): Soils that have high infiltration 

rates even when thoroughly wetted and a high rate of water transmission. Typical 

maximum infiltration rate of 10 inches per hour when dry and 0.5 in/hr when 

saturated. 

Hydrologic Soil Group B (moderately low runoff potential): Soils that have 

moderate infiltration rates when thoroughly wetted and a moderate rate of water 

transmission. Typical maximum infiltration rate of 8 in/hr when dry and 0.4 in/hr 

when saturated. 
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Hydrologic Soil Group C (moderately high runoff potential): Soils that have a 

slow infiltration rate when thoroughly wetted and a slow rate of water transmission. 

Typical maximum infiltration rate of 5 in/hr when dry and 0.25 in/hr when saturated. 

Hydrologic Soil Group D (high runoff potential): Soils having very slow 

infiltration rates when thoroughly wetted and a very slow rate of water transmission. 

Typical infiltration rate of 3 in/hr when dry and 0.10 in/hr when saturated. 

In many cases in Florida, dual hydrologic soil group classifications (A/D or B/D) are 

assigned to soils that, during the wet season, are saturated throughout much of the soil 

column due to a high surficial water table. Thus, during this time of year, infiltration is 

impeded and the soil acts as a D soil. However, during the rest of the year, when the 

water table is lower, the soil acts as an A or B soil. 

Figure 2.1-3 presents a composite hydrologic soil group classification map of the 

Stevenson Creek watershed. It can be seen from the map that soils within the basin are 

predominantly classified as A and B/D. Group A soils occur on upland sand ridges and 

group B/D soils occur on low lying areas and flat areas with poor natural drainage around 

natural waterbodies and wetlands. A composite breakdown of the hydrologic soil group 

acreage and percentages for the basin is as follows: 

Table 2.1-3 Hydrologic Soil Group Acreages and Percentages 

Hydrologic Soil Group Total Area 

(acres) 

Percentage of Basin 

(%) 

A 2424 38.6 

B 21 0.3 

B/D 2158 34.3 

C 1114 17.7 

D 370 5.9 

Water 199 3.2 

Total 6286 100.0 
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(Figure 2.1-3) 
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The following table presents the Runoff Curve Number Computation Matrix used by 

the ArcView/ArcInfo Geographic Information Systems (GIS) software to compute the 

overall area-weighted curve number for each subbasin. In this method, a unique curve 

number is assigned to each possible combination of hydrologic soil group and land use 

category. The computer program then computes an area-weighted value based on the 

percentages of these soil/land use combinations found within the particular subbasin. 

Table 2.1-4 Runoff Curve Number Computation Matrix 

 Land Use Classification Hydrologic Soil 

Group 

Runoff Curve 

Number 

Commercial A 89

Commercial B 92 

Commercial C 94 

Commercial D 95 

Commercial B/D 94 

Cropland and Pastureland A 49 

Cropland and Pastureland B 69 

Cropland and Pastureland C 79 

Cropland and Pastureland D 84 

Cropland and Pastureland B/D 79 

Forest A 36 

Forest B 60 

Forest C 73 

Forest D 79 

Forest B/D 73 

High Density Residential A 77 

High Density Residential B 85 

High Density Residential C 90 

High Density Residential D 92 

High Density Residential B/D 90 

Industrial A 81 

Industrial B 88 

Industrial C 91 

Industrial D 93 

Industrial B/D 91 

Institutional A 81 

Institutional B 87 

Institutional C 91 
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Table 2.1-4 (Continued) Runoff Curve Number Computation Matrix 

 Land Use Classification Hydrologic Soil 

Group 

Runoff Curve 

Number 

Institutional D 93

Institutional B/D 91 

Low Density Residential A 50 

Low Density Residential B 65 

Low Density Residential C 76 

Low Density Residential D 87 

Low Density Residential B/D 76 

Medium Density Residential A 61 

Medium Density Residential B 75 

Medium Density Residential C 83 

Medium Density Residential D 86 

Medium Density Residential B/D 83 

Open Land and Rangeland A 39 

Open Land and Rangeland B 61 

Open Land and Rangeland C 74 

Open Land and Rangeland D 80 

Open Land and Rangeland B/D 74 

Specialty Farms A 59 

Specialty Farms B 74 

Specialty Farms C 82 

Specialty Farms D 86 

Specialty Farms B/D 82 

Transportation, Communications, and Utilities A 78 

Transportation, Communications, and Utilities B 83 

Transportation, Communications, and Utilities C 88 

Transportation, Communications, and Utilities D 90 

Transportation, Communications, and Utilities B/D 88 

Water W 100 

Wetland A-D 98 

Wetland W 100 

Overall CN values were calculated for each subbasin using the above matrix and GIS 

intersection analysis. In order to derive the percent impervious area for each subbasin, a 

“pervious area” CN was created for each subbasin based only on its soil type and its 

pervious area land use. For example, medium density residential was shown as open land 

and range land to represent the lawns and open space. By comparing the overall CN to 
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the pervious area CN, a total percent impervious area for each subbasin was backcalculated using using an excel spreadsheet. Then, based on the percent of total 

impervious as DCIA (derived through the calibration process), the curve numbers were 

recomputed using only the unconnected impervious area. The excel spreadsheet used for 

this analysis is included in Appendix A. 

2.1.2.5 Time of Concentration 

The time of concentration (TC) is a measure of the time scale of the runoff 

hydrograph and is a function of subbasin slope and surface roughness. Conceptually, it is 

the time required for the hydrologically most distant point in the subbasin to begin 

contributing flow to the subbasin outlet, following the commencement of rainfall. The 

time of concentration for each subbasin within the Stevenson Creek watershed was 

computed using the Kinematic Wave approach as outlined in SCS Technical Release 55. 

In this method, the TC is computed as the sum of travel times for sheet flow, shallow 

concentrated flow, and open channel flow. The reader is referred to chapter 3 of SCS 

Technical Release 55 in Appendix E for further details on this method. 

2.1.3 Hydraulic Model Development 

The hydraulic model used for this study was AdICPR, which contains a onedimensional unsteady flow hydraulic routing model. This model uses a node-reach 

representation of the drainage system. AdICPR receives hydrograph input at specific 

nodes by file transfer from the hydrologic model. The model performs dynamic routing 

of stormwater flows through the defined storm drainage system to the points of outfall in 

the receiving waterbody. The program will simulate branched or looped networks; 

backwater due to tidal or non-tidal conditions; free-surface flow; pressure flow or 

surcharge; flow reversals; flow transfer by weirs, orifices, and pumping facilities; and 

storage. Types of reaches that can be simulated include pipes, weirs, open channels of 

regular or irregular cross section, bridges, and drop structures (weir and pipe in series). 
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Simulation output takes the form of water surface elevations and discharges at each node 

and reach within the model network, reported at user-specified time intervals. 

2.1.3.1 Drainage Facility Inventory 

The initial and most important step in the development of the hydraulic model of the 

Stevenson Creek watershed was the inventory of the drainage structures along the 

primary drainage system. This information provides the foundation for the model 

representation of the hydraulic system. The drainage facility inventory of the study area 

was compiled from an array of sources and methods. Hydraulic data for culverts, storm 

sewers, bridges, control structures, and watercourse cross sections were obtained from 

city drainage atlas mapping, development plans, roadway plans, previous studies, and 

field surveys. Data collected included elevations, lengths, dimensions, construction 

materials, channel vegetation, structure entrance and exit conditions, and other pertinent 

features. The following is a discussion of the sources and methods used to collect this 

information: 

Existing Maps, Plans and As-Builts

The City of Clearwater maintains 1”=100’ scale drainage atlas maps that include 

considerable detail of locations, dimensions, and invert elevations of drainage facilities 

located within the incorporated city limits. These maps are periodically updated as new 

development occurs or new information is obtained, and provide a great deal of detail 

within the areas they cover, including secondary storm sewer systems. Invert elevations 

are not always indicated, however, and there is no information shown for the 

unincorporated areas within the basin. The City of Dunedin storm atlas provides a 

similar degree of mapping of drainage facilities. 

It was previously noted that the SWFWMD stormwater management facility permit 

files were researched to collect information on facilities constructed within the Stevenson 

Creek watershed since the inception of the permit regulations in 1984. The City of 

Clearwater, Pinellas County, and the City of Dunedin also provided record drawings of 
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drainage and flood control works that have been constructed within the basin. In 

addition, the Stevenson Creek Sediment Evaluation with Cross Sections completed by the 

City of Clearwater in August 1999 provided many of the irregular cross sections used in 

the model. The following list contains the most noteworthy plans, maps and as-builts 

used as sources of existing hydraulic model input data used in the development of the 

Stevenson Creek hydraulic model: 

• Pinellas-Anclote Basin Aerial Photography with Contours. March 1977, May 

1979, and December 1985, Southwest Florida Water Management District. 

• City of Clearwater Stormwater Atlas. 1996-1999, City of Clearwater Public 

Works Administration, Engineering. 

• City of Dunedin Stormwater Atlas. 1999, City of Dunedin Engineering Section 

• Stevenson Creek Sediment Evaluation with Cross Sections. August 1999, City of 

Clearwater Public Works Administration, Engineering. 

• Spring Branch of Stevenson’s Creek Drainage Basin Field Survey Notes. March 

1979, Pinellas County Engineering Department. 

• Stevenson’s Creek Watershed Channel Improvements, Phase 1 As-Built Plans. 

February 1993, W.K. Daughtery Consulting Engineers, Inc. 

• Stevenson Creek – Channel Improvements – Phase II Plans. March 1995, Camp, 

Dresser and McKee. 

• Highland Avenue Stormwater Improvements As-Built Plans. November 1998, 

HDR Engineering, Inc. 

• The Mall From Union Street to the South Terminus Record Drawings. July 1994, 

Seminole Engineering. 

• 3rd Avenue Drainage Improvements Record Drawings. March 2000, City of 

Dunedin Department of Public Works and Utilities. 

• Villas at Renaissance Square (Old Sunshine Mall) Construction Plans. January 

1999. Florida Design Consultants, Inc. 

• Various MSSW and ERP permit information on file with the Southwest Florida 

Water Management District. 
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Previous Studies

The Stevenson Creek watershed has been the subject of several stormwater 

management studies in the last 20 years that served as valuable sources of information on 

the existing structures and channels along the primary drainage system of the basin. 

These sources were used to varying degrees to supplement and/or confirm other sources 

to provide the required AdICPR model input data to describe the primary drainage system 

and facilities in the watershed. 

The first of these studies was a storm drainage basin study conducted in 1981 by 

Henningson, Durham, and Richardson, Inc. (HDR) for Pinellas County. This study was a 

part of the countywide comprehensive stormwater drainage master plan, which has since 

been adopted within the Pinellas County Comprehensive Plan in its Drainage Element 

(1989). To conduct its study of the Stevenson Creek basin, HDR used the SCS TR-20 

computer model for hydrologic analysis. Runoff hydrographs were developed for each 

subbasin in the watershed, using existing and comprehensive future land use, with the 25-

year, 6-hour duration storm event of 5.5 inches total precipitation used as the basis for 

design. The U.S. Army Corps of Engineers HEC-2 model was used to perform backwater 

analyses to determine flood profiles for each of the design storm events. The Pinellas 

County Study also served as the basis for a Master Drainage Plan for the Spring Branch 

Watershed, prepared in 1983 by the City of Dunedin Public Works Department. For this 

study, Parsons ES used selected information from the original Pinellas County field 

survey notes as needed to augment the structure and cross section information within the 

City of Dunedin portion of Spring Branch. 

In 1988, a Preliminary Master Plan for Stevenson Creek was prepared by W.K. 

Daughtery, Inc. for the City of Clearwater. In the 1988 study, a three-phase channel 

improvement project was recommended for the main channel of Stevenson Creek. The 

modeling methodology employed TR-20 to generate runoff hydrographs for the 5-, 10-, 

25-, 50-, and 100-year, 24 hour duration storm events. The hydrographs were then input 

to a one-dimensional, steady-flow water surface profile model (WSP-2) to calculate the 
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flood elevations. In 1990-1991, Camp, Dresser, and McKee, Inc. (CDM) prepared a 

limited re-study of Stevenson Creek under which the TR-20/WSP-2 model was converted 

to AdICPR, Version 1.4. The AdICPR model was then used to support the detailed 

design of portions of the preliminary master plan project, as well as a FEMA Letter of 

Map Revision (LOMR). This re-study by CDM also included analysis of alternatives for 

floodplain enhancements within the Glen Oaks Golf Course. To date, two of the three 

phases of the original project have been constructed, consisting of the channel segments 

between Betty Lane and Jeffords Streets. The previously referenced as-built plans for 

these channel improvements were relied upon extensively in the development of the 

model. 

The following list summarizes the previous and on-going studies of the Stevenson 

Creek Watershed which were consulted in the development of this watershed 

management plan: 

• Summary Report for Stevenson’s Creek Preliminary Master Plan. August, 1988, 

W.K. Daughtery Consulting Engineers, Inc. 

• City of Clearwater 1997 Watershed Management Plan, Volume II. Post, 

Buckley, Schuh & Jernigan 

• Stevenson Creek Channel Improvements, Phase 2 – Joint Dredge and Fill Permit 

Application. April 1992, Camp, Dresser, and McKee 

• Technical information submitted to FEMA in support of request for Stevenson 

Creek Letter of Map Revision. May 1998, Camp, Dresser and McKee. 

• Pinellas County Storm Drainage Basin Study Technical Appendix – Spring 

Branch of Stevenson Creek Basin and Coastal Zone 4 Basin. October 1981, 

Henningson, Durham & Richardson, Inc. 

• Repetitive Loss Report – City of Clearwater, FL. October 1998, FEMA 

• Master Drainage Plan: Spring Branch Watershed. September, 1983, City of 

Dunedin Public Works Department, Water Resources. 

• Stevenson Creek Sediment Characterization and Removal Feasibility Study - 

Final Report. August 1998, BCI, Inc. 
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• Stevenson Creek Estuary – Preliminary Restoration Plan. October 2000, U.S. 

Army Corps of Engineers, Jacksonville District 

Field Reconnaissance and Field Survey

Field reconnaissance of the Stevenson Creek watershed was conducted by driving 

and walking the basin to determine drainage patterns, map drainage facilities, measure 

facility dimensions inspect the condition of the drainage facilities in the field, assemble a 

photographic log of drainage facilities, and to confirm information collected from the 

previously discussed sources and/or resolve differences between different sources. 

Following completion of the field reconnaissance, Parsons ES developed a field 

survey plan to establish the size, location, dimensions and inverts of drainage structures, 

and to define current stream channel and floodplain cross sections within the Stevenson 

Creek watershed based on the specific needs of the hydraulic model. The emphasis of 

this survey was placed on areas within the basin where there were no available sources of 

as-built record drawings and surveys. The survey program was conducted by Harry 

Marlow, Inc., under the direction of Parsons ES. In addition, the City of Dunedin 

conducted limited surveys of selected structures and cross sections for use in the portion 

of the model that lies within the limits of the City of Dunedin. 

2.1.3.2 Channel Cross Section and Floodplain Definition 

A variety of sources of channel cross section and drainage structure data were 

utilized in the formulation of the AdICPR model. Parsons ES used what was judged to be 

the most current, detailed, and representative source of information available for any 

particular reach of the open channel system. In addition, the extension of channel crosssections into the floodplain regions of the Stevenson Creek floodway was necessary for 

many of the surveyed cross-sections obtained from the various sources. In these 

instances, the SWFWMD one-foot contour topographic maps were used to scale off the 

floodplain extensions. 
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One of the most important requirements of the hydraulic model representation of 

open channel reaches is the selection of an appropriate channel roughness coefficient, or 

Manning’s n, value. This is an index of the resistance to flow, primarily due to friction, 

that is dependent upon factors such as the extent and type of channel vegetation, channel 

bottom material, channel irregularity, channel alignment, obstructions, and depth of flow. 

Selection of an appropriate Manning’s n value for a particular channel reach is a 

subjective procedure that is facilitated by past experience. As a first step in this 

procedure, Parsons ES personnel took color photographs of all open channel reaches 

within the model. Published guides and past modeling experience were then applied in 

the selection of channel and floodplain Manning’s n values. These values were either 

confirmed or adjusted during the model calibration process using the rating curves of the 

streamflow gaging stations and the measured high water elevations. 

2.1.3.3 Storage Node Stage-Area Relationships 

In order to represent the attenuating effects of storage on the hydrographs computed 

by the hydrologic model, it is important that all significant stormwater storage areas and 

their hydraulic controls features be well defined within the model. This is especially 

important in the Stevenson Creek watershed where much of the drainage throughout the 

basin is controlled by lakes (man-made and natural) and natural depression areas. The 

AdICPR model allows the user to specify a variable stage-area relationship at any model 

node that defines the storage properties at that point, be it a pond, lake, wetland, or other 

water body. 

In the development of the Stevenson Creek watershed hydraulic model, Parsons ES 

used, where available, record drawings and permits as a means of establishing stage-area 

relationships of constructed stormwater management facilities. For all others, including 

the natural lakes, ponds, and wetlands within the watershed, the stage-area relationships 

were determined by direct measurement of SWFWMD one-foot topographic maps with a 

planimeter. 
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2.1.3.4 Model Schematic 

The hydraulic model (AdICPR) of the Stevenson Creek watershed consists of a 

network of open channel segments, culverts, bridges, storm sewers, weirs, lakes, ponds, 

and wetlands that compose the primary drainage system within the basin. AdICPR uses a 

link-node concept to idealize the “real world” drainage system. A node is a discrete 

location in the drainage system where conservation of mass (continuity) is maintained. 

Links, or “reaches” are the connections between nodes and are used to convey water 

through the system. The entire network of nodes and reaches forms the hydraulic model 

network and serves as the computational framework for AdICPR. 

The first step in development of a model schematic was to identify the primary 

drainage system and all drainage facilities within it. This task was accomplished through 

the research and review of all available sources of information that have been previously 

described, and through field reconnaissance of the entire watershed. All such information 

was compiled and a watershed drainage map developed which depicts the primary 

drainage system. Figure 2.1-1, included in the attached map pocket, presents the drainage 

map of the Stevenson Creek watershed and the model node locations which were used to 

define the primary conveyance network of the basin. General guidelines which were 

followed in development of the model schematic are: 

• Nodes are required at the upstream and downstream ends of any structure (e.g. 

culvert, bridge, weir, etc.). 

• Storage elements (ponds, lakes, wetlands, etc.) are specified as nodes. 

• Nodes are located at tributary confluence locations. 

• Nodes are placed at locations where there is a major surface water inflow to the 

conveyance system. 

• Points of change in channel geometry and/or slope are specified as node 

locations. 
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• Nodes are added at locations within the network to define the hydraulic 

gradeline in greater detail. 

When constructing a model network, unique identifiers must be assigned to all nodes 

and reaches. The node-numbering scheme is the same as the subbasin numbering scheme 

previously described, except that node identifiers begin with the letter “N”. By 

convention, the identification of a reach between two nodes is the same as the name of 

the upstream node. Reach identifiers begin with a letter prefix pertaining to the type of 

reach as follows: 

Reach Type Prefix 

Channel C 

Pipe P 

Weir W 

Drop Structure DS 

Bridge BR 

Overland Flow Channel COF 

Overland Flow Weir WOF 

A node-reach schematic of the AdICPR model of the Stevenson Creek watershed is 

provided in Figure 2.1-4, contained within the attached map pocket. This schematic 

represents the hydraulic network as it is modeled. Storage nodes and type of reaches are 

indicated as they are represented within the AdICPR model. The schematic includes 

“overflow” reaches which model the overland flow paths that floodwaters can follow 

when flow rates exceed the capacities of the primary drainage system. In all, the model 

includes 383 nodes, 252 pipe reaches, 176 open channel reaches, 171 irregular cross 

sections, 98 weir reaches, 39 drop structure reaches, and 6 bridge reaches. 
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2.1.3.5 Boundary Conditions 

The AdICPR model requires specification of hydraulic boundary conditions at all 

outfall points of the model schematic. In the Stevenson Creek watershed application, the 

primary basin outlet is located at the downstream face of the most downstream bridge at 

Edgewater Drive (Alt. US 19). A constant tailwater boundary condition representing the 

water elevation of Clearwater Harbor, a tidal waterbody, was specified at elevation 2.5 

feet above mean sea level, 1929 National Geodetic Vertical Datum (NGVD) for all model 

simulations. This elevation was intended to approximate a “spring tide” condition within 

the harbor. It should be noted that for flow rates above approximately 3,000 cfs (which 

applies to the peak rates of flow for all design storms), the existing conditions stages 

within the Stevenson Creek estuary were not found to be sensitive to changes in the tidal 

boundary condition over a range of 0 to 3 feet NGVD. 

 An “overflow” boundary node exists at the northern end of the Jeffords Street 

Branch where floodwaters can “pop off” to the Allens Creek Basin when the flows 

exceed the capacity of the storm sewers. A third boundary node exists at the Clearwater 

Executive Airport, where a 36” diameter CMP culvert under the runways diverts a 

portion of the flow from the headwaters of Hammond Branch east into the Alligator 

Creek Basin. The tailwater elevations at these overflow boundary nodes are allowed to 

fluctuate with normal depth in the boundary link. Modeling results from the completed 

Allens Creek and Alligator Creek Watershed Plans were consulted to determine whether 

flooding was predicted in those watersheds which would influence stages in the 

corresponding Stevenson Creek boundary nodes. These model results indicated that the 

design flood elevations are well below the Stevenson Creek “pop-off” elevations, 

therefore it was not necessary to code in the time/stage boundary conditions based on 

these other models. 
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2.1.4 Model Calibration and Verification 

2.1.4.1 Introduction 

Model calibration refers to the adjustment of model parameters within reasonable 

limitations so that the model results (i.e., streamflows and water elevations) are in 

reasonable agreement with a set of measured data. A reasonable range of values for the 

adjustment of model parameters is established through the review of literature references, 

and adjustments outside of those ranges are made only if some unusual hydrologic or 

hydraulic condition exists. Ideally, the model is calibrated to more than one different 

storm event in order to represent a variety of volumes, intensities, and distributions. It is 

also desirable to calibrate to recorded flow and stage information at different locations 

within the watershed. 

The two primary data requirements for model calibration and verification are gaged 

rainfall and streamflow for the study area. When selecting a calibration storm event, the 

rainfall and streamflow data must be sufficiently documented in appropriate time 

intervals so that variations in rainfall intensity and the associated runoff can be accurately 

simulated. Data should be recently acquired so that the current land use and hydraulic 

conditions existing in the study area are accurately represented. Additionally, because of 

the non-uniform spatial distribution inherent in Florida rainfall patterns, it is desirable 

that precipitation data be collected at more than one location within a large study area. 

2.1.4.2 Streamflow and Precipitation Gaging Data 

Prior to the initiation of this watershed management plan, no known measured 

streamflow data existed for Stevenson Creek. Therefore, it was necessary to collect 

streamflow data for calibration of the hydrologic/hydraulic computer model. This was 

accomplished by establishing two streamflow gaging stations within the Watershed. 

Continuous rainfall, stage, and streamflow data were collected under the direction of 

Parsons ES by Hydrogage, Inc. at Stevenson Creek near Drew Street and at Spring 

Branch near King’s Highway. The locations of the stations are shown on Figure 2.1.5. 
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(Figure 2.1-5)
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 The streamflow data was collected in digital format from May 12, 2000 to October 

12, 2000. Stream stage (water level) was recorded at 15-minute intervals using a 

calibrated pressure transducer. Rainfall amounts were recorded at 15-minute intervals 

using a standard tipping-bucket rain gage. The rainfall data recorder utilized a telemetry 

system to alert Hydrogage of storm events in progress. Streamflow measurements were 

made over a wide range of flow conditions using standard USGS stream gaging 

procedures. These measurements were then correlated to recorded stage elevations to 

establish a flow versus stage rating curve at each location. 

In addition to the precipitation and streamflow data, storm event flow-weighted 

composite water samples were collected with the aid of automatic samplers at each 

station. The water quality monitoring program is described in detail in Section 2.3.2. 

2.1.4.3 Selection of Calibration/Verification Storm Events 

July 15, 2000

Due to the relatively short period of record, only a handful of storm events was 

available for calibration of the model. Fortunately for this analysis, the period of record 

captured a large storm that occurred on July 15, 2000. This storm produced 7.60” and 

5.21” of total rainfall within a ten-hour period at the Drew Street and King’s Highway 

sites, respectively. As evident from Figure 2.1-6, this storm consisted of two separate 

rainfall events occurring approximately 6 to 7 hours apart. The first event occurred from 

about 7:00 AM to 10:00 AM and produced 3.23” at the Drew Street site and 1.69” at the 

King’s Highway site. At 2:00 PM, the second event occurred, producing 4.37” at the 

Drew Street site and 3.52” at the King’s Highway site. All of the rainfall in the afternoon 

event fell within a 2-hour period from 2:00 PM to 4:00 PM. The peak 15-minute 

intensity occurred at about 2:30, averaging 7.44 and 4.04 inches per hour at the Drew 

Street and King’s Highway sites, respectively. This storm produced widespread flooding 

throughout Stevenson Creek and the City of Clearwater. Following this event, staff from 
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(Figure 2.1-6) 
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Parsons ES and the City marked visible high water elevations at 21 locations throughout 

the basin, which City survey personnel later surveyed (three of the elevations marked in 

the field as “questionable” were later discarded). 

Because the hydrologic model chosen for the analysis is intended to be used strictly 

as a single-event model, the larger, afternoon rainfall event was chosen as a calibration 

event. By inspection of Figure 2.1-6, it is evident that both Stevenson Creek and Spring 

Branch responded to the two storms as separate and distinct events. It should be noted, 

however, that the first event served to substantially increase the soil moisture leading into 

the second event. Prior to the morning of July 15, hydrologic conditions within the 

watershed were still extremely dry due to the several months of drought during the spring 

of 2000. 

June 12, 2000

In order to compliment and verify the large storm event of July 15, a smaller storm 

was chosen in order to verify the calibration parameters, and to “fine-tune” the DCIA 

percentages. For these purposes, the storm of June 12, 2000 was chosen, which produced 

0.85 and 0.54 inches of rainfall at the Drew Street and King’s Highway stations, 

respectively. The antecedent moisture conditions preceding this event were extremely 

dry. The total rainfall amounts were therefore small enough to make the assumption that 

all runoff due to this storm was contributed by the DCIA, and thus all rainfall in areas 

outside the DCIA was lost to infiltration. 

2.1.4.4 Calibration Parameters and Results 

When calibrating a computer model, certain model input parameters are held 

constant while others are adjusted in attempt to produce reasonable agreement with 

measured data. Those parameters that are adjusted are referred to as calibration 

parameters. Since it is desirable to limit the number of calibration parameters to the 

fewest possible, those parameters that can be easily measured or calculated normally are 

not adjusted. Calibration parameters are typically those coefficients and or indexes that 
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are not easily determined from known quantities and/or established procedures. The two 

primary calibration parameters chosen for the Stevenson Creek model are runoff peak rate 

factor for the hydrologic component, and channel Manning’s roughness for the hydraulic 

component of the model. 

When calibrating a model which uses the SCS unit hydrograph and runoff curve 

number method, it is often necessary to adjust the runoff curve number (CN) in order for 

the model to match the measured runoff volume. This is primarily due to the fact that the 

selected calibration storm events may have antecedent moisture conditions which differ 

significantly from typical design values found in the literature, which are conventionally 

based on either average, or average wet season, conditions. Runoff volumes can be very 

sensitive to CN, especially in southwest Florida where the sandy soils and seasonally high 

water table can result in a wide range of CN values depending on the time of year (i.e, 

wet season versus dry season). However, no CN adjustment was necessary for the 

Stevenson Creek calibration since the runoff volumes predicted for the July 15th storm 

using CN’s corresponding to average antecedent moisture conditions matched the 

observed volumes fairly well. This is due to the likelihood that the first of the two 

rainfall events on July 15th served to increase the soil moisture conditions from dry 

conditions to something closer to typical design conditions. 

Channel Mannings Roughness

The primary means of calibrating the AdICPR hydraulic model was through 

adjustment of the Mannings Roughness Coefficient, or Mannings “n”. This is an index of 

the resistance to flow through a channel, primarily due to friction, that is dependent upon 

factors such as the extent and type of channel vegetation, channel bottom material, 

channel irregularity, channel alignment, obstructions, and depth of flow. Adjustments to 

the channel Mannings “n” were made to the cross sections in the vicinity of the 

streamflow gages until the simulated flow versus stage rating curve provided a reasonable 

match with streamflow measurements made during a number of different storm events 
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and flow conditions. No adjustments were made to the Manning’s roughness in the 

vicinity of the Spring Branch at King’s Highway station however, since within the range 

of the measurements, the flow appears to be controlled by the box culverts under King’s 

Highway (refer to Figure 2.1-7). The simulated rating curve at this location provided a 

reasonable fit to the measured data without any adjustment to the Mannings “n” values. 

 Figure 2.1-7 Box Culverts Downstream of King’s Highway Monitoring Station 

At the Drew Street gage in Stevenson Creek, it was necessary to increase the in-bank 

Mannings “n” from the initial estimate of 0.07, to 0.09 for the cross section immediately 

downstream of the gage in order to match the measured data. In a field visit in March of 

2000, this section was observed to be heavily vegetated (refer to Figure 2.1-8), although 

the degree of vegetation in the channel generally decreased in the sections further 

downstream through the golf course. Of course, the degree of vegetation varies not only 

with location, but also with time of year and point in the maintenance cycle. 
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Figure 2.1-8 Vegetation in Channel Downstream of Drew Street 

Monitoring Station 

Figures 2.1-9 and 2.1-10 illustrate the simulated flow versus stage rating curves at 

Drew Street and King’s Highway, respectively. Note that the dependant variable (flow) is 

plotted on the X-axis. The measured values are plotted for comparison. 

Following calibration of the Peak Rate Factor (described below), the channel 

Mannings “n” values were adjusted at several other locations in the watershed in order to 

match the surveyed high water elevations of the July 15th flood event. 

Peak Rate Factor

In the SCS Unit Hydrograph Method, a composite unit hydrograph is constructed of 

several incremental triangular unit hydrographs that adhere to the basic SCS triangular 

unit hydrograph equation: 

qp = K’AQ

 Tp 
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(Figure 2.1-9 and 2.1-10) 
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Where qp = peak runoff rate in cfs, 

 A = area in square miles, 

 Q = rainfall excess depth in inches, 

 K’ = runoff peak rate factor 

 The runoff peak rate factor, K’, includes a unit conversion and a hydrograph shape 

factor which determines the respective fractions of the runoff volume occurring under the 

rising and falling limbs of the hydrograph. The value of K’ has been shown to vary 

widely, from 100 in extremely flat basins in South Florida, up to 600 in steep, 

mountainous terrain. It has been suggested that K’ varies with watershed surface storage 

and/or average watershed slope. However, since no definitive relationship between 

subbasin slope and K’ has been proposed, it is often used as a calibration parameter. In 

the absence of gage data, the SCS recommends using a value of 256 for Florida, and 484 

for most of the rest of the country. It can be shown that a K’ of 484 corresponds to 3/8 

and 5/8 of the runoff volume occurring on the rising and falling limbs of the hydrograph, 

respectively. A K’ of 256 corresponds to 1/5 and 4/5 of the runoff volume occurring on 

the rising and falling limbs, respectively. The lower peak rate factors produce longer 

recession limbs with a smaller peak discharge rate for the same unit volume of runoff. It 

should be noted that these empirical values were derived from regional studies of small 

groups of similar watersheds, and are not necessarily applicable when applied outside 

their experimental ranges. 

 For the Stevenson Creek watershed, a value of 256 was used as the initial estimate of 

K’ for all subbasins, in accordance with the SCS recommendation for Florida. However, 

this value tended to produce simulated hydrograph shapes that suggested that the K’ value 

was too low. The K’ was increased to 484 for several of the steeper subbasins throughout 

the watershed, including several along the main channel of Stevenson creek which had 

average slopes exceeding 3%. Those subbasins with average slopes of less than about 1% 

were left with their original K’ of 256. This adjustment produced better agreement with 

the observed hydrograph shapes. Figures 2.1-11 and 2.1-12 provide a comparison 

between the simulated and measured hydrographs for the storm of July 15, 2000. 
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(Figure 2.1-11 and 2.1-12) 
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 Once the model was calibrated to match the observed hydrograph shape, the 

Mannings “n” was adjusted for the remaining cross sections throughout the watershed, in 

order to provide a closer match to the surveyed high water elevations. The following 

table compares the simulated and the measured high water elevations of the flood of July 

15, 2000: 

 

Table 2.1-5 Comparison of Measured and Simulated High Water Elevations 

Storm of July 15, 2000 

Peak Stage (ft NGVD '29) Difference

Node ID Node Location Measured Simulated (ft) 

1000 Spring Branch at King’s Highway gage 12.51 12.48 -0.03 

1040 Spring Branch at Union Street (u/s) 16.45 16.36 -0.09 

2030 Hammond Branch Pond at King’s Highway 13.16 13.47 0.31 

2130 Flagler Ditch at Saturn Avenue 61.10 61.11 0.01 

2300 Smallwood Circle and Rosewood Road 45.98 46.08 0.10 

3000 Stevenson Creek at Drew Street gage 14.12 14.14 0.02 

3040 Stevenson Creek at Cleveland Street (u/s) 18.04 17.81 -0.23 

3090 Stevenson Creek at Court Street (d/s) 18.61 18.83 0.22 

3100 Stevenson Creek at Court Street (u/s) 18.97 18.88 -0.09 

3120 Stevenson Creek at Druid Road (d/s) 20.76 20.60 -0.16 

3125 Stevenson Creek at Druid Road (u/s) 20.67 20.82 0.15 

3700 Lake Belleview outfall structure at Lakeview 40.22 40.13 -0.09 

4020 Stevenson Creek at Browning Street (u/s) 30.05 30.21 0.16 

4040 Stevenson Creek at Lakeview Road (u/s) 31.16 31.14 -0.02 

4080 Stevenson Creek at St. Thomas Drive (u/s) 39.53 39.52 -0.01 

4090 Stevenson Creek at Belleair Road (d/s) 39.80 39.58 -0.22 

4100 Stevenson Creek at Belleair Road (u/s) 40.08 40.12 0.04 

4140 Jeffords Street Branch at Highland Avenue 28.73 28.73 0.00 

4160 Jeffords St Branch at Skyview and Jeffords 31.14 30.70 -0.44 

4190 Jeffords Street Branch at Barry and Tuscola 30.80 30.67 -0.13 
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 All of the simulated high water elevations were within 0.50 feet of the measured 

values, which is within the accuracy of computation for this type of analysis, and exceeds 

FEMA’s minimum requirements for flood insurance studies. All except two of the values 

were with 0.25 feet of the measurements. 

Model Verification and DCIA 

 The storm of June 12, 2000 was simulated in order to verify the calibration 

parameters and to fine-tune estimates of DCIA as a percentage of total impervious area. 

As mentioned in previous sections, total impervious area within each subbasin was 

estimated based on land use and aerial photography. A 50/50 split between directly and 

non-directly connected impervious areas was initially assumed. Since runoff volumes 

resulting from high intensity, large volume storm events normally are not sensitive to the 

percentage of total impervious as DCIA, a small, less intense storm event was chosen for 

DCIA determination. Since the storm of June 12 was a low volume, low intensity storm 

that had extremely dry antecedent moisture conditions, all runoff from this storm can 

reasonably be attributed to DCIA. The initial model simulation slightly under predicted 

the volume from this storm. The percentage of total impervious as DCIA was then raised 

from 50% to 65%, which resulted in a better fit with the measured hydrographs (refer to 

Figures 2.1-13 and 2.1-14). The 15% impervious area that was transferred into DCIA 

was subtracted from the calculations of weighted CN, resulting in slightly lower CN 

values. Then, the calibration storm of July 15 was simulated with the new CN and DCIA 

values. As expected, the results from the larger storm event did not change significantly. 

2.1.5 Flooding Conditions Assessment 

Upon the successful completion of the development and calibration of the detailed 

hydrologic and hydraulic model, the next step of the watershed management planning 

process was to apply the model to assess the performance of the basin drainage network 

for a given set of design storm events. Results of these simulations were then analyzed 

with respect to the flooding level of service criteria, in order to identify the locations and 

the severity of potential flooding problems. 
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(Figure 2.1-13 and 2.1-14) 
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2.1.5.1 Design Storm Events 

The basis for the evaluation of flooding conditions in the watershed were the 10, 25, 

50, and 100-year return period, 24-hour duration design storm events. The total rainfall 

for these events are 7.5, 9.0, 10.5, and 12.0 inches, respectively, as determined from the 

SWFWMD Environmental Resource Permitting (ERP) Information Manual (February 

1996). The 500-year, 24-hour storm was also simulated in order to be consistent with 

FEMA mapping guidelines. The rainfall of 14.8 inches for the 500-year storm was 

determined through a probability analysis of the more frequent design storm events. The 

SCS Type II Florida-Modified rainfall distribution was used to develop the design storm 

hyetographs for the all return periods. 

2.1.5.2 Existing Flooding Conditions 

Using the described design storm events as the basis for simulations, the AdICPR 

model was run to generate predictions of basinwide flooding conditions for the existing 

conditions throughout the Stevenson Creek watershed. The results of these model 

simulations are summarized in Appendix D, Table D.1. This table lists the model nodes 

in sequence starting from the downstream end and the corresponding model predictions 

of 10-, 25-, and 100-year flood elevation at those locations. Also listed are the locations 

and descriptions of the adjacent roadways and the low road elevation at each structure. 

Note that the low road elevation does not necessarily occur at the exact location of the 

structure itself, since sags along the road profile, as determined from SWFWMD 

topographic mapping and/or roadway construction drawings, may occur several hundred 

feet away in certain instances. When a peak flood elevation exceeds the low road 

elevation, it indicates that the roadway will be inundated at that location by a depth 

corresponding to the difference in elevations. 
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Comparison with Previous Studies

The following table compares the simulated 100-year flood elevations and peak 

discharge rates at five key locations within Stevenson Creek to the previous analyses of 

the watershed: 

Table 2.1-6 Comparison of 100-year Peak Discharge Rates and Flood Stages 

 Location 

W.K. Daugherty 1988 

Preliminary Master Plan, 

Future Conditions

CDM 1997 

FEMA Submittal

Parsons ES 

Existing Conditions

100-yr Flow 

(cfs) 

100-yr Stage 

(ft, NGVD)

100-yr Flow 

(cfs) 

100-yr Stage 

(ft, NGVD)

100-yr Flow 

(cfs) 

100-yr Stage 

(ft, NGVD)

 Douglass Avenue 5,859 4.6 n/a n/a 4,697 7.73 

 Palmetto Street 4,603 11.0 2,190 8.67 3,300 10.14 

 Drew Street Gage 3,718 15.5 2,030 12.75 2,848 15.70 

 S. of Court Street 3,075 22.8 1,280 19.58 2,588 22.89 

 Jeffords Street 2,574 28.0 1,724 25.00 1,998 28.24 

Because the modeling completed for this study was calibrated to measured stage and flow 

data, and the level of detail in the model network is an order of magnitude higher than the 

modeling completed for the previous studies, differences in the results are to be expected. 

Comparison of the peak discharge rates shows that those predicted by the Watershed 

Management Plan model consistently fall between those predicted by the other two 

studies. Upstream of Palmetto Street, the flood elevations predicted by the Parsons ES 

model generally compare closely with the W.K. Daugherty future conditions model, 

which includes the phase 1, 2, and 3 improvements (of which only phases 1 and 2 were 

constructed). In these same locations, the flood elevations predicted both in this study 

and in the W. K. Daugherty study are approximately three feet higher than those reported 
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in the 1997 CDM study. While the reason for this large difference was not readily 

discernable, it should be mentioned that the 100-year project conditions flood levels 

reported in the 1997 CDM FEMA submittal are 0.5’ to 2.5’ lower than the 25-year project 

conditions flood levels reported in the 1992 CDM dredge and fill permit application (not 

shown). In addition, when comparing flood elevations at Douglass Avenue and Palmetto 

Street, it should be noted that neither of the two previous studies included the modeling 

of bridges at Edgewater Drive and the Pinellas Trail. In addition, the CDM study did not 

include the bridge at Douglass Avenue. 

2.1.5.3 Flooding Level of Service Criteria 

For the development of the comprehensive watershed management plan for the 

Stevenson Creek watershed, it was necessary to establish flood protection level of service 

(FPLOS) criteria by which flooding problems can be identified and alternatives for flood 

control can be evaluated. Determination of appropriate FPLOS criteria is therefore a very 

important part of the watershed planning process. Once the design storm flood elevations 

have been determined through the comprehensive modeling procedures, the FPLOS 

criteria then become the primary factor in determining the cost taxpayers must bear in 

order to remedy the existing flooding problems. Thus, the FPLOS criteria become the 

point at which the cost of infrastructure improvements is balanced against the public’s 

desire to further reduce the flooding in the watershed. 

 The primary FPLOS criterion is that there is to be no structural flooding (i.e., homes 

and businesses) for events up to and including the 100-year flood. This criterion refers to 

the low floor slab elevation (lowest inhabited floor) as the point of structural flooding. 

This is consistent with FEMA guidelines, and has been widely adopted by counties and 

municipalities across the state and the country. 

 The secondary set of FPLOS criteria specifies allowable thresholds for street 

flooding. The criteria is based upon residential, collector, and arterial roadways being 

passable for the 10, 25, and 100-year flood events, respectively. For the purposes of this 
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study, “passable” is defined as 6” of flooding or less at the lowest edge of pavement in a 

travel lane. No flooding is allowable on hurricane evacuation routes for events up to and 

including the 100-year flood. The following table summarizes the proposed FPLOS 

criteria for Stevenson Creek: 

Table 2.1-7 -- Proposed Flood Protection Level of Service (FPLOS) Criteria for the 

Stevenson Creek Basin 

FPLOS Category Allowable Flooding Depths 

1. Residential Streets, 2 lanes Up to 6” Allowed for 10-year flood 

2. Collector Roads, 2-4 lanes Up to 6” Allowed for 25-year flood 

3. Arterial Roads, 4 or more lanes Up to 6” Allowed for 100-year flood 

4. Hurricane Evacuation Routes No flooding up to 100-year flood 

5. Habitable Structures No flooding up to 100-year flood 

In the next section, the above FPLOS criteria is used to identify and develop 

potential projects to reduce the design flood elevations to within the allowable flooding 

depths. However, experience shows that improving infrastructrue to reduce flood depths 

to meet a desired level of service is not always cost effective. For this reason, project 

costs must be weighed against the relative benefits. Of course, multiple-use facilities 

provide benefits in addition to flood control which must also be considered, as will be 

discussed in subsequent sections. Projects which do not provide benefits commensurate 

with the costs will not be recommended for funding. 

Furthermore, it is not always technically feasable to reduce flood depths to meet a 

desired level of service. For example, many structures in low-lying areas near the coast in 

Clearwater were erected prior to the community’s participation in the National Flood 

Insurance Program, which first began in 1968. Many of these structures are subject to 
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saltwater inundation from the 100-year storm (hurricane) surge from the Gulf of Mexico. 

Although beyond the scope of this Watershed Management Plan, it is highly unlikely that 

an infrastructure project designed to protect against the 100-year storm surge in this area 

would be technically feasable. 

In instances such as these where it is not cost effective or technically feasable to 

lower the floodplain, alternatives to flood level reduction should be considered. One such 

alternative would be a program which allows the city, in cooperation with FEMA, to 

assist willing property owners in the floodproofing, elevating, or purchase of flood prone 

structures. 

2.1.5.4 Flooding Problem Identification 

The limits of the 100-year floodplain were generated by delineating the predicted 

flood elevations on SWFWMD 1”=200’ one foot contour aerial maps. Within the lower 

tidal portions of Stevenson Creek, the mapped floodplain limits are governed by FEMA’s 

computed storm surge elevations, as they are higher than those predicted to occur from 

riverine (freshwater) flooding due to rainfall and runoff. The storm surge floodplain 

intersects with the riverine floodplain near the Palmetto Street crossing of Stevenson 

Creek. 

The floodplain limits were digitized for incorporation into the GIS, as illustrated in 

Figure 2.1-15 in the rear map pocket. The 500-year floodplain was mapped per FEMA 

requirements and is shown for informational purposes only. Although the hydrologic and 

hydraulic modeling necessarily included the entire watershed, including areas outside the 

corporate limits of the City of Clearwater, floodplain limits within the City of Dunedin 

were not mapped. Riverine flood profiles were plotted for the 10, 25, 50, 100, and 500-

year design storm events for Stevenson Creek and Spring Branch, as shown on Figures 

2.1-16 through 2.1-24 at the end of this section. 

Flood protection level of service deficiencies were identified in the watershed area 

within the corporate limits of the City of Clearwater. The street flooding level of service 
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deficiencies for the basin are tabulated in Appendix D, Table D.1. Shaded cells indicate 

locations that currently do not meet the proposed FPLOS criteria. The locations of the 

street FPLOS deficiencies are shown graphically on Figure 2.1-15. 

In order to determine the number and location of structure FPLOS deficiencies, 

habitable structures within the limits of the 100-year floodplain were identified. A 

determination was then made as to which homes and businesses were likely to be 

susceptible to flooding for the 100-year event. This determination was based on the 

assumption that the floor elevations for slab-on-grade type structures are at least 6 inches 

above adjacent ground as shown on the SWFWMD aerials. Using this proceedure, 470 

structures were identified as potentially flood susceptible. In order to more accurately 

approximate the actual number of structure FPLOS deficiencies, surveyed finished floor 

information was compiled for the majority of these structures. Surveyed elevations for 

approximately 75 of the structures were obtained as part of the 1988 W.K. Daugherty 

study. An additional 272 structures were surveyed by Harry Marlow, Inc., as part of this 

study. The remaining 123 structure elevations were estimated from the SWFWMD 

topography and the surveyed elevations of nearby structures. 

Of the 470 structures entered into the database, 263 structures were found to have 

finished floor elevations below the 100-year flood level. This is, by definition, a structure 

flooding level of service deficiency. As indicated on Figure 2.1-15, the majority of these 

structures are located within the primary floodplains of the Stevenson Creek and Spring 

Branch main channels. However, many of the identified FPLOS deficiencies result from 

inadequate secondary drainage systems that feed into the main channels. 

Table D.2 in Appendix D provides a complete listing of the structure flooding level 

of service evaluation for the Stevenson Creek Watershed. A summary of the identified 

structure FPLOS deficiencies in terms of both structures and total dwelling units is 

provided below as Table 2.1-8. Because many of the structures are multi-family 
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buildings (duplexes, apartment buildings, etc), the number of flood-susceptible dwelling 

units is larger than the number of flood susceptible structures. 

Table 2.1-8 Summary of Structure Flooding Level of Service Deficiencies 

Subwatershed Identified 100-year FloodSusceptible Structures Identified 100-year FloodSusceptible Dwelling Units 

Spring Branch 32 32 

Lower Stevenson Creek 32 32 

Middle Stevenson Creek 49 105 

Upper Stevenson Creek 85 85 

Hammond Branch 6 6 

Lake Bellevue Branch 14 23 

Jeffords Street Branch 45 51 

Total 263 334 

Subwatershed 1: Spring Branch 

The Spring Branch Subwatershed was found to contain 32 structure FPLOS 

deficiencies. The majority of these (27) are in the area of Byram Drive and Flora Drive 

between King’s Highway and Highland Avenue, and along Huntington Lane, east of 

King’s Highway. These FPLOS deficiencies are located in a depressional area bordering 

the historical Spring Branch channel. At Woodlawn Terrace, east of Douglass Avenue, 

an additional four structure FPLOS deficiencies were identified in an isolated 

depressional area drained by an inadequate secondary storm sewer system. These two 

areas were identified in the 1997 City of Clearwater Watershed Management Plan, 

through interviews with City staff in the Engineering Department, as “areas of concern 

for flooding”. Sunset Point Baptist Church was also identified as a level of service 
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deficiency. Four residential street FPLOS deficiencies and eight collector road FPLOS 

deficiencies were identified, including Douglass Avenue, King’s Highway, Sunset Point 

Road (two locations) and Highland Avenue. Although not FPLOS deficiencies of the 

City of Clearwater, there are estimated to be 10-15 flood-susceptible homes along Betty 

Lane and Macomber Avenue, north of Sunset Point Road within unincorporated Pinellas 

County. The locations of the City of Clearwater FPLOS deficiencies are shown on Figure 

2.1-15. 

Subwatershed 2: Lower Stevenson Creek 

In the Lower Stevenson Creek Subwatershed, 32 structure FPLOS deficiencies were 

identified. The majority of these (27) are located along the main channel of Stevenson 

Creek between Douglass Avenue and Palmetto Street. These homes and businesses all 

have floor elevations below 9.5 feet NGVD, and are susceptible to flooding from both 

riverine flooding (rainfall and runoff) and storm (hurricane) surge. The 100-year storm 

surge elevation, as determined from the FEMA Flood Insurance Rate Maps, is elevation 

11.0, NGVD. In addition to the structures susceptible to both flooding sources, there are 

several additional structures between Edgewater Drive and Palmetto Street which are 

susceptible to storm surge flooding only, which were not included. Other structure 

FPLOS deficiencies in Lower Stevenson Creek include two utility buildings adjacent to 

the Creek in the Clearwater Country Club. Also identified were two relatively isolated 

structure FPLOS deficiencies in the North Greenwood area and one near the intersection 

of Palmetto Street and King’s Highway. The latter three FPLOS deficiencies are far 

removed from the creek, and are the result of inadequate secondary drainage systems. 

Residential street FPLOS deficiencies were identified at seven locations, and collector 

road FPLOS deficiencies were identified at six locations, including Douglass Avenue, 

Fairmont Avenue (two locations), Palmetto Street (two locations), and North Greenwood 

Avenue (refer to Figure 2.1-15). 
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Subwatershed 3: Middle Stevenson Creek 

In terms of the concentration of flood-susceptible dwelling units, the most severe 

flooding problems in the watershed occur within the Middle Stevenson Creek 

subwatershed. Approximately 49 structures consisting of 105 ground-floor dwelling units 

along the banks of Middle Stevenson Creek were identified that are subject to inundation 

from the 100-year design flood. Many of the structures are multi-family buildings. All of 

the FPLOS deficiencies identified in this subwatershed are adjacent to the main channel 

of the Creek between Drew Street and Jeffords Street. The majority (60) of these 

structure FPLOS deficiencies occur in the area immediately to the west of Glen Oaks 

Golf Course. To provide an idea of the magnitude of the flood problem in this area, 24 

dwelling units were also found to be vulnerable to the 25-year flood. In addition, three 

homes were found susceptible to the 10-year flood, including two homes in the 600 block 

of Betty Lane, which have been the subject of documented structure flooding. The most 

notable street FPLOS deficiency occurs at Cleveland Street, a hurricane evacuation route, 

at its crossing of Stevenson Creek. The predicted flood depths are more than two feet 

above the roadway for the 100-year flood. The roadway would also be impassable for a 

25-year flood, and minor flooding is predicted for a 10-year flood. Residential street 

FPLOS deficiencies were identified at five locations, including Pierce Street, Franklin 

Street, Betty Lane (2 locations), and Mark Drive. 

Although the construction of the Phase 1 and Phase 2 improvements in the 1990’s 

significantly improved the conveyance capacity of Stevenson Creek from Drew Street to 

Court Street, floodplain enhancements within the Glen Oaks Golf Course were never 

constructed to the level originally envisioned in the 1990-1991 re-study of Stevenson 

Creek by CDM. In addition, the effectiveness of the constructed conveyance 

improvements has been greatly diminished due to a lack of adequate maintenance. Layers 

of sediment, and at times dense vegetation, have occupied portions of the improved 

channel. This problem was observed to be most severe between Drew Street and 

Cleveland Street. 
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Subwatershed 4: Upper Stevenson Creek 

Upper Stevenson Creek encompasses the portion of the Creek targeted for 

conveyance improvements in Phase 3 of the 1988 W.K. Daugherty study. This phase was 

never constructed, primarily due to environmental concerns over the proposed 

improvement method of hardlining (paving) the channel with concrete. In the current 

analysis, the Upper Stevenson Creek subwatershed was found to contain 85 structure 

FPLOS deficiencies. All of these lie within the floodplain of the main channel of 

Stevenson Creek, with the largest concentration of them occuring on both sides of the 

Creek between Jeffords Street and Lakeview Avenue, and along Hillcrest Avenue south 

of Lakeview Road (see Figure 2.1-25). 

Figure 2.1-25 Flooding on Hillcrest Avenue, South of Lakeview Road 

Storm of July 15 , 2000

However, the most severe and frequent flooding in the subwatershed occurs along 

Evergreen Avenue between Bellevue Boulevard and St. Thomas Drive, where seven 
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homes were found susceptible to the 10-year flood. According to the City’s complaint 

logs, at least two of these structures flooded during the recent storm of July 15, 2000. 

The flooding problem at this location is due to a 54” CMP culvert placed within the 

Stevenson Creek Channel that lacks the capacity to convey even the mean annual storm 

event. Residential street FPLOS deficiencies were identified at seven locations, and 

collector road FPLOS deficiencies were identified on Belleair Rd and Highlands Avenue. 

Subwatershed 5: Hammond Branch 

Hammond Branch was found to contain six structure FPLOS deficiencies, the fewest 

of all the subwatersheds. All of the FPLOS deficiencies are a result of inadequate 

secondary drainage systems. A single structure FPLOS deficiency on Hibiscus Street 

near King’s Highway occurs when the storage capacity of the Hibiscus Pond is exceeded 

due to inflows from a 54” RCP culvert from the Highland Avenue drainage system. The 

existing outfall of Hibiscus Pond, consisting of a gunited 30” CMP, is not adequate to 

handle the inflows from the Highland’s Avenue culvert. An unrelated problem occurs on 

Smallwood Circle (southeast of Highland and Palmetto), where two structure FPLOS 

deficiencies were identified. These homes were built in a depressional area surrounding a 

small city park, which floods frequently during moderate to heavy rains. The depression 

is drained by an undersized, failing 24” CMP culvert which runs under existing homes on 

Elmwood Street and Smallwood Circle. In addition, three FPLOS deficiencies were 

identified on Linwood Drive near Sharondale Drive, on the north side of the CSX railroad 

that runs parallel to Flagler Drive. This problem area is the result of floodwaters from the 

Flagler Drive ditch backing up through twin 48” RCP culverts under the CSX railroad. 

The 48” culverts were intended to convey runoff from the subbasin to the north into the 

Flagler ditch. During flood events, however, the culverts flow in the opposite direction, 

directing floodwaters from the south side of the railroad, across the flood susceptible 

properties bordering Linwood Drive. The problem is exacerbated by the fact that the 

floor elevations of the homes are only two to three feet above the invert of the Flagler 

Drive Ditch. 
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Residential street FPLOS deficiencies were identified at twelve locations in the 

Hammond Branch Subwatershed. Collector road FPLOS deficiencies were identified at 

nine locations, including three locations on King’s Highway, four locations on Highland 

Avenue, and two locations on Palmetto Street. 

Subwatershed 6: Lake Bellevue Branch 

Incrementally over past several decades, the Lake Bellevue Branch has been almost 

completely enclosed in storm sewer. Unfortunately, little of the storm piping was 

designed to adequately handle major a storm event. In the Lake Bellevue Branch 

Subwatershed, 14 structures consisting of 23 ground-floor dwelling units were found 

susceptible to inundation from the 100-year design flood. Of this total, five are 

businesses located on Missouri Avenue immediately south of Turner Street. Missouri 

Avenue itself constitutes an arterial road FPLOS deficiency at this location. This 

flooding problem is due to the fact that upstream of Missouri Avenue, the Lake Bellevue 

Branch flows into a 54” diameter culvert which lacks the capacity to convey the flow 

resulting from even a mean-annual storm event. Further upstream in the subwatershed, 

four structure FPLOS deficiencies occur at Pinellas Street, east of Greenwood Avenue, 

and one on Tuskawilla Street, west of Greenwood Avenue. These FPLOS deficiencies 

are also the result of undersized culverts placed within the historic channel of the Lake 

Bellevue Branch. Upstream of Lake Bellevue, four flood-susceptible structures 

containing a total of 13 dwelling units were identified on Wildwood Way, west of the 

CSX railroad. These structures were built in a low area southwest of the Lake. The 

drainage for this area is towards Lake Bellevue, but flows are restricted by undersized 

culverts beneath the CSX railroad tracks. In addition to the single arterial road FPLOS 

deficiency on Missouri Avenue, the Lake Bellevue Branch contains five collector road 

FPLOS deficiencies on Druid Road, South Greenwood Avenue (two locations), Lakeview 

Road, and Belleair Road, and six residential street FPLOS deficiencies. 
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Subwatershed 7: Jeffords Street Branch 

Within the Jeffords Street Branch Subwatershed, 45 structures containing 51 

dwelling units were found susceptible to the 100-year flood. The majority of these 

structures (35 of 45) are located within a contiguous floodplain area that encompasses the 

Jeffords Street ditch and the three interconnected lakes in the vicinity of Duncan Avenue 

and Jeffords Street. Historical 1926 aerial photography shows a wetland existed where 

these structures and lakes are today. It is likely that material dredged to form the three 

lakes was used as fill to form the building lots and roadways in the former wetland. 

However, the area is still extremely floodprone, as evidenced by the numerous 

documented complaints of flooding, and the mapped extent of the 100-year floodplain. 

The remaining structure FPLOS deficiencies (10 structures/16 dwelling units) were also 

constructed in a former wetland, in the area now bounded by Spencer Avenue, Turner 

Street, Duncan Avenue, and Druid Road. These structures flood on a very frequent basis, 

as seven are below the 10-year flood level and nine of the ten are below the 25-year flood 

level. According to the City’s complaint logs, at least two of these structures flooded 

during the recent storm of July 15, 2000. Collector road FPLOS deficiencies were 

identified on Highland Avenue, Lake Avenue (two locations), and Cleveland Street at 

Duncan Avenue. In addition, seven residential street FPLOS deficiencies were identified, 

most of which lie within the large contiguous floodplain area that encompasses the 

Jeffords Street Ditch. 

• Figure 2.1-17 Stevenson Creek Flood Profile, Existing Conditions

• Figure 2.1-18 Stevenson Creek Flood Profile, Existing Conditions

• Figure 2.1-19 Stevenson Creek Flood Profile, Existing Conditions

• Figure 2.1-20 Stevenson Creek Flood Profile, Existing Conditions

• Figure 2.1-21 Stevenson Creek Flood Profile, Existing Conditions

• Figure 2.1-22 Stevenson Creek Flood Profile, Existing Conditions

• Figure 2.1-23 Spring Branch Flood Profile, Existing Conditions
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• Figure 2.1-24 Spring Branch Flood Profile, Existing Conditions
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2.2 NATURAL RESOURCES ASSESSMENT AND PROBLEM 

IDENTIFICATION 

2.2.1 Introduction 

In order to prepare the Watershed Management Plan for the Stevenson Creek 

Watershed, the entire watershed was investigated for undeveloped land, wetlands, natural 

areas, and potential restoration or preservation areas. The boundaries of the natural areas 

were identified and mapped on aerial photography (scale: 1” = 200’). These areas were 

characterized using the Florida Land Use Cover and Forms Classification System 

(FLUCCS) (FDOT, 1985). 

The Stevenson Creek Watershed is a highly urbanized, densely populated area with 

little to offer in the way of natural systems. With one exception, the only undeveloped 

areas are golf courses and city parks. Wetlands are predominantly small isolated 

stormwater retention ponds or natural lakes that have been altered to such a degree that 

their origin can only be determined from historic aerial photography. The waterways are 

predominantly channelized with little riparian habitat. The intense development has also 

altered the estuarine system so that little habitat is provided at the mouth of Stevenson 

Creek. 

Despite the intense urbanization of the watershed, improvements that do not require 

large expanses of open land and large expenditures of public funds can be made to 

increase the wildlife habitat and improve water quality. Studies have shown that golf 

courses can be managed to improve the water quality and wildlife habitat provided by the 

expanses of open space without negatively impacting the recreational function. For the 

purposes of this watershed management plan, a discussion of the existing natural 

conditions is provided in this section, while improvements that can be accomplished by 

public entities, private non-profit organizations, and by concerned private citizens are 

discussed in Section 3. 
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2.2.2 Existing Conditions 

As can be seen in the land use map (Figure 2.1-2) and Table 2.2-1, the predominant 

land use within the watershed is residential, comprising approximately 70% of the total 

land area. Other developed areas such as commercial, industrial, institutional, open land, 

and transportation/utility land uses combined make up another 19% of the watershed. 

This leaves only 11% of the watershed in potential natural resource land uses, which 

includes undeveloped upland areas, recreational areas, open water bodies, or wetlands. 

Most of the individual subwatersheds are similar in distribution of land uses. The 

Upper Spring Subwatershed has more wetlands than any other subwatershed, with 40 

acres compared to less than 7 acres for each of the other subwatersheds. This is due to 

two large forested wetland areas near the intersection of Keene Road and Virginia Street. 

A 36-acre upland forested area in the Lower Spring Branch Subwatershed is by far the 

largest available habitat area in the watershed. The other subwatersheds have 0 to 7 acres 

of undeveloped uplands that may provide habitat. The open water bodies land use, which 

includes ponds, lakes, and other open water areas, is divided among three subwatersheds 

that have only 7 acres and four subwatersheds that have between 22 and 56 acres. The 

following paragraphs provide a subwatershed-by-subwatershed description of the land 

uses and available habitat. 

Upper Spring Branch Subwatershed 

The Upper Spring Subwatershed is located in the northernmost portion of the 

watershed and is the largest in total land area. There are several forested wetland areas 

within the watershed, as well as a freshwater marsh. 

The freshwater marsh (approximately 4 acres) is located west of the forested 

wetland areas near the intersection of Virginia and Keene. The marsh is highly disturbed 

and dominated by nuisance vegetation such as primrose willow, cattail, and others. Some 

open water is present in the center of the marsh, indicating a depth that may be associated 
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Table 2.2-1 

LAND USE TYPES PER BASIN IN THE STEVENSON CREEK WATERSHED 

(Approximate acreages) 

Land Use Hammond 

Branch 

Jeffords 

Street 

Lake 

Belleview 

Lower 

Spring 

Lower 

Stevenson 

Middle 

Stevenson 

Upper 

Spring 

Residential (1000-

1300) 649 529 340 338 516 287 1226 

Commercial 

(1400) 34 31 178 11 56 145 115 

Industrial 

(1500) 5 4 13 0 20 00 0 

Institutional 

(1700) 21 14 16 23 31 11 53 

Recreational 

(1800) 96 40 24 0 116 45 18 

Open Land 

(1900) 41 2 13 37 11 11 105 

Agriculture 

(2000) 10 0 0 0 0 0 5. 

Upland Forests 

(4000) 2 0 5 36 0 0 7 

Water Bodies 

(5000) 27 22 37 8 40 7 56 

Wetlands 

(6000) 1 1 7 7 5 2 40 

Trans./Utilities 

Communication 

(8000) 

27 8 22 5 27 27 47 

Total per Basin 914 651 655 465 821 535 1673 
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with historic activities such as peat mining or excavation to increase retention and/or to 

reduce the ground water levels in adjacent properties. Development is encroaching upon 

the marsh, with new housing constructed on the east side. In its current state, this marsh 

still can provide wildlife habitat, although the isolated, fragmented condition of the marsh 

has greatly reduced the potential. 

The 30 acres of forested wetlands appear to be the former headwaters of Spring 

Branch, which flows from this area south and west to the confluence with Stevenson 

Creek. These forested wetlands have been substantially altered with dredging, draining, 

filling, and channelizing. The canopy consists of a mixture of hardwoods and cypress, 

with slash pine in the drier transitional areas. The vegetation in these wetlands has been 

impacted by the hydrologic alterations, and nuisance species are now dominant in some 

areas. 

Lower Spring Branch Subwatershed 

The Lower Spring Branch Subwatershed is located north and east of the confluence 

of Stevenson Creek and Clearwater Harbor. This is the smallest of the subwatersheds, at 

only 465 acres. Although this subwatershed is 80% developed, there are two areas within 

this subwatershed that offer habitat to wildlife. In addition, portions of the Spring Branch 

channel still maintain a remnant of riparian habitat in the form of trees and a somewhat 

natural streambed. 

The forested upland area within this watershed is located near the intersection of 

Sunset Point Road and Betty Lane. This approximately 25-acre parcel has been impacted 

in the past with clear-cutting and grading. Historic aerial photography (1926) shows that 

this parcel was cleared and a pond was excavated on the west side, potentially in 

preparation for development. The southern portion of the parcel supports a stand of 

second-growth oak and pine with an open understory. Spring Branch borders the east 

side of this portion of the parcel. The northern, more mesic portion of the parcel supports 

more nuisance vegetation, especially around the pond and the outer edges of the site. 

However, there are mature trees in the canopy and native species in the understory and 
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shrub layer. The vegetation in the pond is dominated by Carolina willow, and appears to 

be intermittently inundated. 

Despite the impacted condition of the parcel, it currently provides the only wildlife 

habitat of any substantial size within the watershed. Recent survey lines cut through the 

parcel indicate that it may be too late to preserve it, but it has the potential to become 

locally significant wildlife habitat, as well as a neighborhood recreational area. 

This photo was 

taken facing north 

from the ditch that 

drains the small 

excavated pond 

within the forested 

area at Betty Lane 

and Sunset Point 

Drive. 

This photo was 

taken in the mesic 

forested area, in 

the southern part 

near State Street. 

The vegetation in 

this area includes 

slash pine, laurel 

oak, saw palmetto, 

and cabbage palm. 
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Lower Stevenson Creek Subwatershed 

This subwatershed is 80% developed in residential, industrial, commercial, and 

utility/transportation land uses. Fourteen percent of the watershed is identified as 

recreational, but this includes a ballpark and the Clearwater Country Club. There are no 

large tracts of undeveloped upland areas that may provide habitat for wildlife, and few 

areas that would provide wetland habitat. There is a small (approximately 9-acre) parcel 

of land east of the Douglas Avenue Bridge on the north side of Stevenson Creek that 

provides the best potential habitat in the subwatershed. The parcel appears to have been a 

dumping ground for construction material, fill, household waste, and landscape 

trimmings. The majority of the site is vegetated with nuisance exotic species such as ear 

tree (Enterolobium contortisiliquum), lead tree (Leucaena leucocephala), Caesar weed 

(Urena lobata), castor bean (Ricinus communis), beggar’s tick (Bidens pilosa), Australian 

pine (Casuarina equisetifolia), Brazilian pepper (Schinus terebinthifolius), and other 

noxious weeds. Some remnants of native upland vegetation are present on the eastern 

boundary, adjacent to the auto-salvage yard along the eastern boundary of the 

undeveloped parcel. Species present in this area include laurel oak (Quercus laurifolia), 

saw palmetto (Serenoa repens), cat briar (Smilax bona-nox), and wild grape (Vitis sp.). 

The shoreline of the parcel along Stevenson Creek is vegetated in mangroves, 

including black (Avicennia germinans) and red (Laguncularia racemosa). A small 

mangrove swamp is located on the western side of the property. This swamp is 

predominantly black mangrove with an open water area in the center. The City is 

currently in negotiations with the owner to purchase the property containing this parcel. 
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Stevenson Creek meanders through the Clearwater Country Club golf course on a 

semi–natural streambed. There have been previous attempts to create marsh habitat online with the creek that have been somewhat successful. On-line wetlands are always 

difficult to create because of the need to accommodate the occasional heavy volumes of 

water flowing through the stream and the potential for erosion. In addition, maintenance 

is difficult due to the nuisance exotic vegetation that can be washed in from problem 

areas upstream. In spite of the drawbacks, the golf course provides one of the best 

potential areas for habitat improvement, depending upon the available area. 

The photo to the 

left was taken on 

the north bank of 

Stevenson Creek 

west of the 

Douglas Avenue 

Bridge. The 

view is to the 

southeast 

This photo 

shows the 

mitigation area 

within the golf 

course. The 

low gabion wall 

was installed to 

protect the 

mitigation area 

from erosion 

and the influx 

of exotic 

vegetation. 
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Middle Stevenson Creek Subwatershed 

The Middle Stevenson Creek Subwatershed is 90% developed, with golf courses 

and a few stormwater ponds comprising the remaining ten percent. This subwatershed 

has the second highest area devoted to commercial enterprises, but no industrial land 

uses. There are no potential habitat areas with the exception of the golf courses, which 

provide marginal habitat at best. The creek is armored and channelized through this 

portion of the watershed, and although these types of improvements may be essential for 

flood abatement, they do little to enhance water quality and wildlife habitat. 

Hammond Branch Subwatershed 

This second largest subwatershed is located on the east side of the watershed, with 

the majority of the subwatershed lying north of Drew Street. This subwatershed is 87% 

developed, with a golf course and ball fields again comprising the majority of the 

undeveloped land. There are three fairly large water bodies in the subwatershed totaling 

27 acres. These managed water bodies and two very small freshwater marshes provide 

the best habitat options in the subwatershed. 

The photo to the 

left shows a typical 

section of the creek 

(Lynn Lake) 

through the Middle 

Stevenson Creek 

Subwatershed. 

The algal mats on 

the water surface 

usually indicate 

poor water quality.
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Jeffords Street Subwatershed 

The Jeffords Street Subwatershed is located in the eastern portion of the watershed, 

south of the Hammond Branch Subwatershed. This watershed is 91% developed with 

several water bodies and a golf course making up the remaining land uses. Crest Lake, 

the 20+-acre lake in the northern portion of the subwatershed, is located within a city 

park. This lake and the surrounding shoreline could potentially be enhanced to increase 

the habitat potential without impacting the park significantly. A discussion of these 

improvements and Best Management Practices for golf courses is provided in Section 3. 

There are several small water bodies in the subwatershed ranging in size from 0.5 to 

4.0 acres. These ponds are located within dense residential neighborhoods and likely do 

not provide more than the most minimal habitat for wildlife. Even small ponds can be 

improved to enhance the wildlife habitat availability by planting the shoreline with native 

species and improving water quality by reducing the pollutants in stormwater runoff. 

The photo to the 

left shows a view 

of Lake Hobart 

facing south. This 

lake is one of the 

larger water 

bodies. 
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Lake Bellevue Branch Subwatershed 

The Lake Belleview Subwatershed is located in the southwestern portion of the 

Stevenson Creek Watershed, with Missouri Road roughly forming the eastern boundary. 

The subwatershed is 89% developed, with the 33-acre Lake Bellevue comprising another 

5% and the adjacent park and playgrounds adding another 5%. 

This recreational area (Ed Wright Park) is the only potential wildlife habitat in the 

Subwatershed, but the habitat is marginal at best. The lake is maintained to keep aquatic 

weeds from overtaking, however on the west side of the lake, the banks are covered with 

Brazilian pepper and other noxious invasive plants. These weeds do provide some 

function acting as a buffer from the heavy traffic on Myrtle Avenue. The northeast corner 

of the park supports a heavy canopy of mature oaks, but the understory is predominantly a 

parking area. 

There are six small water bodies in the subwatershed, excluding Lake Bellevue. 

As with the majority of the other small water bodies in the watershed, these are highly 

maintained, isolated, and located within dense residential neighborhoods. These areas 

provide marginal habitat at best. 

This photograph is a 

view of Crest Lake 

from the northeastern 

corner. The 

sparseness of the 

understory 

vegetation can 

contribute to erosion 

and sedimentation in 

the lake due to 

stormwater runoff. 
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Upper Stevenson Creek Subwatershed 

The Upper Stevenson Creek Subwatershed is located in the southeastern portion of 

the watershed with Missouri Avenue forming the western boundary. This subwatershed 

is completely built out, with the exception of four small water bodies totaling 7 acres. 

The creek is completely lined with houses, leaving no options for habitat improvements 

without purchasing expensive residential property. 

This photograph of 

Lake Bellview shows 

the bare shorelines 

and lack of 

significant littoral 

vegetation. The 

littoral vegetation 

would provide 

habitat and water 

quality benefits. 

This photograph was 

taken on the 

southwestern corner 

of the lake and 

shows the nuisance 

vegetation 

infestation. 

Cleaning up this area 

would enhance the 

wildlife habitat 

provided by this

area. 
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2.2.3 Wildlife 

This highly urbanized area does not provide much habitat for wildlife, other than for 

generalist species that have adapted to urban environments. Table 2.2-2 provides a list of 

common faunal species that were observed or are expected to occur in the watershed. 

The Backyard Habitat program promoted by the National Wildlife Federation 

educates citizens on building habitat within their own backyards, which increases the 

available habitat in urban environments. Details on this program are available on the 

National Wildlife Federation website. 

2.2.4 Endangered and Threatened Species 

Endangered and threatened species are those that have been categorized in some 

way by the respective jurisdictional agencies as meriting special protection or 

consideration. The state lists of animals are maintained by the Florida Fish and Wildlife 

Conservation Commission and categorized as endangered, threatened or of special 

concern. The lists constitute Rules 39-27.003, 39-27.004, and 39-27.005, respectively, 

Florida Administrative Code. 

This is an example 

of one the culverts 

within the Upper 

Stevenson Creek 

Subwatershed. 

This culvert is near 

the intersection of 

Hillcrest and 

Browning. 
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Table 2.2-2 

Wildlife Observed (*) or Expected Within the Stevenson Creek Watershed 

Scientific Name Common Name 

Birds

Accipiter cooperii Cooper’s hawk 

Agelaius phoeniceus* Red-winged blackbird 

Ajaia ajaja* Roseate spoonbill. 

Anas fulvigula* Mottled duck 

Anhinga anhinga* Anhinga 

Ardea herodias* Great blue heron 

Aramus guarauna Limpkin 

Bombycilla cedrorum* Cedar waxwing 

Botaurus lentiginosus American bittern 

Bubulcus ibis* Cattle egret 

Buteo lineatus* Red-shouldered hawk 

Butorides virescens* Green heron 

Cardinalis cardinalis* Cardinal 

Casmerodius albus* Great egret

Cathartes aura* Turkey vulture 

Ceryle alcyon* Belted kingfisher 

Chadradrius vociferous* Killdeer 

Colaptes auratus* Northern flicker 

Columba livia* Rock dove 

Coragyps atratus* Black vulture 

Corvus brachyrhynchos* American crow 

Corvus ossifragus* Fish crow 

Cyanocitta cristata* Blue jay 

Dendroica coronata* Yellow-rumped warbler 

Dendroica palmarum Palm warbler

Dryocopus pileatus* Pileated woodpecker 

Dumetella carolinensis* Catbird 

Egretta caerula* Little blue heron 

Egretta thula* Snowy egret 

Egretta tri-color* Tricolor heron 

Elanoides forficatus* Swallow-tailed kite 

Eudocimus albus* White ibis 

Falco sparverius* American kestral 

Falco peregrinus Peregrine falcon 
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Fulica americana* American coot 
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Table 2.2-2 (cont.) 

Wildlife Observed (*) or Expected Within the Stevenson Creek Watershed 

Scientific Name Common Name 

Birds (cont.)

Gallinula chloropus* Common moorhen 

Geothlypis trichas* Common yellowthroat 

Ixobrychus exilis* Least bittern 

Lanius ludovicianus* Loggerhead shrike 

Larus argentatus* Herring gull 

Larus atricilla* Laughing gull 

Larus delawarensis* Ring-billed gull 

Larus philadelphi Bonapart’s gull 

Melanerpes carolinus* Red-bellied woodpecker 

Mimus polyglottus* Mocking bird 

Mycteria Americana* Wood stork 

Nycticorax nycticorax* Black-crowned night heron 

Nyctanassa violacea* Yellow-crowned night heron 

Otus asio* Belted kingfisher 

Pandion haliaetus* Osprey 

Passer domesticus* House sparrow 

Parus bicolor* Tufted titmouse 

Pelecanus occidentalis* Brown pelican 

Phalacrocorax auritus* Double-crested cormorant 

Picoides pubescens* Downy woodpecker 

Plegadis falcinellus Glossy ibis 

Podilmbus podiceps* Pied-billed grebe 

Quiscalus major* Boat-tailed grackle 

Quiscalus quiscula* Common grackle 

Rallus elegans King rail 

Rallus limicola Virginia rail 

Sterna forsteri* Forster’s tern 

Streptopelia decaocto* Eastern screech owl 

Strix varia Barred owl 

Sturnus vulgarus* European starling 

Tachycineta bicolor* Tree swallow 

Toxostoma rufum* Brown thrasher 

Turdus migratorius* American robin 

Thryothorus ludovicianus Carolina wren 
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Zenaida macroura* Mourning dove 
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Table 2.2-2 (cont.) 

Wildlife Observed (*) or Expected Within the Stevenson Creek Watershed 

Scientific Name Common Name 

Mammals

Dasypus novemcinctus* Armadillo 

Didelphis virginiana* Opossum

Lasiurus intermedius Northern yellow bat 

Lontra canadensis River otter 

Peromyscus gossypinus Cotton mouse 

Peromyscus polionotus Oldfield mouse 

Procyon lotor* Raccoon 

Nycticeius humeralis Evening bat 

Sciurus carolinensis* Eastern gray squirrel 

Sciurus niger shermanii Sherman’s fox squirrel 

Sigmodon hispidus Hispid cotton rat 

Sylvilagus floridanus Eastern cottontail 

Sylvilagus palustris Marsh rabbit 

Tadarida brasiliensis Brazilian free-tail bat 

Reptiles And Amphibians

Anolis carolinensis Green anole 

Anolis sagrei sagrei Brown anole 

Acris gryllus Southern cricket frog 

Rana sphenocephala Southern leopard frog 

Bufo terrestris Southern toad 

Coluber constrictor Black racer 

Diadophis punctatus Ring necked snake 

Hyla cinerea Green tree frog 

Hyla gratiosa Barking tree frog 

Hyla squirella Squirrel tree frog 

Osteopilus septentrionalis Cuban tree frog 

Pseudemys floridana floridana Florida cooter 

Rana sphenocephala Southern leopard frog 

Sternotherus sp. Common musk turtle 

Thamnophis sirtalis Common garter snake 

Trachemys scripta elegans Red-eared turtle 

Trachemys scripta scripta Yellow bellied turtle 
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Table 2.2-2 (cont.) 

Wildlife Observed (*) or Expected Within the Stevenson Creek Watershed 

Common Name Common Name 

Fish and Shellfish

Lane Snapper Spotted Sea trout 

Mojarra Silver Sea trout 

Grunt Red Snapper 

Weakfish Yellowtail Snapper 

Gray Snapper Scad 

Atlantic Bumper Silver Perch 

Mutton Snapper Spot 

Lookdown Atlantic Croaker 

Leatherjack Silver Porgy 

Mahogany Snapper Sand Perch 

Permit Gag Grouper 

Black Drum Stone Crab 

Red Drum Tunicate 

Sheepshead Burrfish 

Pinfish Puffer 

Blue Crab Flounder 

Toadfish Hogfish 

Cowfish Wrasse 

Filefish Spadefish 

Sole Black Seabass 

Mullet Glass Slipper 

Parrotfish Squid Egg Mass 

Sergeant Major Comb Jelly 

Snook Sea Urchin 

Gulf Shrimp Bivalve (U.N.I.D) 

Grass Shrimp Sea Snail (Banded Tulip) 

Ghost Shrimp Sea Hare 

Mud Crab Sea Pork 

Hermit Crab Trunkfish 

Arrow Crab Sea Horse 

Pipefish Spade Crab 

Sand Dollar Feather Bleeny 

Lizardfish Scallop 

Spider Crab Sponge 
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Table 2.2-2 (cont.) 

Wildlife Observed (*) or Expected Within the Stevenson Creek Watershed 

Common Name Common Name 

Seabream Octopus 

Shade Crab Polychete Worms 

Scaled Sardine Sea Snail (Moon Snail) 

Wort Jelly Juv. Flying Gunnard 

Horshoe Crab Squid 

Lentil Spider Calico Crab 

Sea Cucumber Mangrove Snapper 

Silverside Whelk Egg

Brittle Star Sea Snail (Banded Tulip)

Source: Clearwater Audubon Society (Ms. Jane Williams), and Clearwater Marine Aquarium 

(Mr. Geoff Lane), field observations (Parsons ES, May 2000), and Florida Natural Areas 

Inventory, 1996 

The state lists of plants are categorized into endangered and threatened and commercially 

exploited and are administered and maintained by the Florida Department of Agriculture 

and Consumer Services via Chapter 5B-40, F.A.C. The federal list of animals and plants 

is administered by the U.S. Fish and Wildlife Service and are published in 50 CFR 17 

(animals) and 50 CFR 23 (plants). 

Even the most urban environments can support some endangered species. For 

instance, during the field reviews for this project, white ibis and little blue heron were 

observed on one of the golf courses within the watershed. Bald eagles have nested in 

other watersheds within the City of Clearwater, and could nest in the Stevenson Creek 

watershed if the appropriate habitat were available. Table 2.2-3 lists the endangered, 

threatened, or species of special concern that occur or potentially occur in the watershed. 
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Table 2.2-3 

Endangered, Threatened, or Special Concern Species Observed (*) 

or Potentially Present in the 

Stevenson Creek Watershed 

Gopher Tortoise Sherman’s fox squirrel* Florida sandhill crane 

Gopher frog Little blue heron* Peregrine falcon* 

American alligator* Wood stork* SE American kestrel 

Florida mouse Tri-colored heron* Bald eagle* 

Eastern indigo snake Snowy egret* Burrowing owl 

Limpkin* Roseate spoonbill* White ibis* 

The species identified with an asterisk (*) in the table above have been observed in 

the watershed by members of the Clearwater Audubon Society. It is highly unlikely that 

any of these species are successfully breeding in or if viable populations of these species 

exist within the Stevenson Creek Watershed due to the lack of suitable habitat. 
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2.3 WATER QUALITY ASSESSMENT 

The Stevenson Creek Watershed is the largest watershed in the City of 

Clearwater. Residential land uses are dominant in this urban watershed, which provides 

drainage for the western portion of Clearwater as well as portions of Dunedin and 

unincorporated Pinellas County. The main stem of the creek originates near Belleair 

Road and flows northward to Clearwater Harbor. 

The largest tributary is Spring Branch which flows from Dunedin and southward 

entering Stevenson Creek just upstream of Clearwater Harbor. Other major tributaries 

include two highly altered streams draining the eastern portion of the watershed. One of 

these streams drains into Stevenson Creek near Palmetto Street and the other empties into 

the creek near Jeffords Street. Another major tributary is a remnant stream that drains 

Lake Belleview and enters the main channel near Glenn Oaks Golf Course. 

Numerous small, natural water storage areas are located throughout the basin as 

well as several lakes. Most notable in size is Lake Bellevue which is around 25 acres. The 

two other largest lakes in the basin are Crest Lake and Lake Hobart which are about half 

the size of Lake Bellevue. 

These storage areas and lakes provide stormwater runoff treatment. Best 

management practices (BMPs) for new (post-1982) development are also present; 

however, stormwater runoff treatment is lacking in many areas. New BMPs can help to 

improve water quality in the watershed; however, anthropogenic sources other than 

stormwater runoff appear to influence water quality in the Stevenson Creek Watershed to 

a significant degree. 

Low dissolved oxygen levels, fecal contamination, and excessive nutrient 

concentrations are the primary water quality issues that have been identified in the 

watershed, and as such, water quality in Stevenson Creek is rated as “poor” by the state. 

The state’s rating is based on sampling conducted by the Pinellas County Department of 
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Environmental Management (PDEM). The city’s ambient monitoring program as well as 

monitoring conducted for this study affirms these water quality issues. 

Stevenson Creek is included on Florida’s impaired waters list {303(d) List} due 

to concerns over dissolved oxygen, coliforms, and nutrients. The FDEP has given 

Stevenson Creek a priority rating of “High”. Stevenson Creek is located in the “Crystal 

River to St. Petersburg Beach Basin” which is in Group 5 of the basin rotation cycle. 

TMDL development activity is expected to begin in 2004. 

Water quality assessments conducted for this study included a 

• Review of Existing Data (Section 2.3.1, Existing Data), 

• Base flow and storm event monitoring program (Section 

2.3.2, Monitoring Program), 

• Water quality data interpretation (Section 2.3.3, Water 

Quality Characteristics), and 

• Nonpoint source loading assessment (Section 2.3.4, 

Nonpoint Source Loads). 

Each of these four elements is described separately in the following subsections. 

2.3.1 Existing Data 

During the last decade, Pinellas County and the city have conducted and 

documented water quality monitoring programs within the Stevenson Creek Watershed 

(Figure 2.3-1); likewise, the Marshall Street Wastewater Treatment plant (MWWTP) 

maintains operating records, and the Pinellas County Health Department maintains 

records concerning individual septic tanks. These monitoring programs and records were 

reviewed and are more specifically described as follows: 

• Pinellas County ambient surface water monitoring 

program-- active Pinellas County monitoring program 

containing two stations within the Stevenson Creek 

Watershed (Refer to Existing Water Quality Monitoring 

Programs, Section 2.3.1.1)
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Figure 2.3-1

Water Quality Monitoring Stations 
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• City of Clearwater ambient surface water monitoring 

program -- ambient surface water quality monitoring 

program from 1992 through 1995 containing ten stations 

within the Stevenson Creek Watershed (Refer to Existing 

Water Quality Monitoring Programs, Section 2.3.1.1) 

• Southwest Florida Water Management District, Lake 

Bellevue monitoring program-- short-term program from 

1996-1997 (Refer to Existing Water Quality Monitoring 

Programs, Section 2.3.1.1) 

• Marshall Street Wastewater Treatment Plant operating 

reports -- ten-year record (Refer to Other Existing Data, 

Section 2.3.1.2) 

• Pinellas County Health Department septic tank records-

- Recent septic tank construction and repair applications 

(Refer to Other Existing Data, Section 2.3.1.2) 

2.3.1.1 Existing Monitoring Programs 

Pinellas County, the Southwest Florida Water Management District (SWFWMD), 

and the City of Clearwater have conducted monitoring programs within the Stevenson 

Creek Watershed. Summary results from each of these monitoring programs are provided 

in Appendix I. 

Pinellas County Department of Environmental Management (PDEM) maintains 

two stations in Stevenson Creek as part of its countywide ambient water quality 

monitoring program. The data from these two stations is the basis for the state’s inclusion 

of Stevenson Creek on the impaired waters list, and the county has used these data to 

implicate Stevenson Creek as having some of the poorest water quality in the county 

(Myers et al. 2000). 

PDEM provided the following description of these two stations to EPA’s 

STORET database: 

• “Stevenson's Creek off the southeast side of the Douglass 

Ave bridge just north of the Clearwater WWTP from mid 

span sampled monthly” 
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• “collected from Spring Branch of Stevenson’s Creek off the 

west side of the Overbrook bridge just west of Douglass 

Ave at mid span sampled monthly” 

Most prominent in each of these data sets are average fecal coliforms counts and 

ammonia nitrogen levels, which often exceed state standards. Phosphorous is high at the 

Spring Branch station, and nitrate + nitrite is high at both stations, particularly at the 

Stevenson Creek Station. The state reports a trophic state index of 65 for the Stevenson 

Creek estuary indicating that water quality is poor. A review of the nitrogen/phosphorus 

ratios shows that the estuary is nitrogen-limited. 

A short-term monitoring program was conducted by SWFWMD on Lake 

Belleview (1996-1997). This program consisted of two sampling events- one in each 

year. The results showed low phosphorous levels for both measurements and high 

nitrogen levels for the 1996-measurement followed by low nitrogen levels during the 

1997-measurement. Accordingly, a sharp drop in lake productivity was observed during 

the second year. Nitrogen forms were almost entirely organic. 

The city conducted an ambient surface water quality monitoring program from 

years 1992 through 1995. The program included 10 stations in the Stevenson Creek 

Watershed. The monitoring program included grab samples analyzed for nutrients, oil 

and grease, suspended solids, coliforms and fecal streptococcus, biochemical oxygen 

demand (BOD5), chlorides, and field parameters (dissolved oxygen, pH, etc.). Dissolved 

oxygen and fecal contamination were the most significant concerns identified for the 

Stevenson Creek Watershed during the city’s monitoring program. Nutrient levels were 

also often elevated during the monitoring period. 

2.3.1.2 Other Existing Data 

Operating reports for Marshall Street Wastewater Treatment plant (MWWTP) 

were reviewed along with limited septic tank information made available by the Pinellas 

County Health Department. These records show that MWWTP (Figure 2.3-2) 

contributes significant quantities of nutrients, solids, and oxygen-demanding substances 

to the Stevenson Creek estuary, and, the septic tank information, considered in 
Stevenson Creek Watershed Management Plan 

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Figure 2.3-2 

Marshall Street Wastewater Treatment Plant 

Y#

Betty Lane

Palmetto Street

/(19

Sunset Point Road

Harbor Drive

Marshall Street

Kings Highway

North Fort Harrison Avenue

ALT

Marshall Street WWTP

Greenwood Street

Pinellas Trail

STEVENSON CREEK

CLEARWATER

HARBOR

SPRING BRANCH

conjunction with coliforms 

sampling results, provides 

information concerning potential 

sources of fecal contamination in 

the basin. 

The MWWTP discharges 

nutrients, solids, and oxygendemanding substances to 

Stevenson Creek. While 

concentrations for these 

constituents in the plant effluents 

are within appropriate standards, 

the average 5.55 MGD-flow (6.8 MGD average daily flow minus 1.25 MGD flow to the 

reclaimed water system) results in masses that make up a significant percentage of total 

loads to the estuary originating from the Stevenson Creek Watershed. Information from 

the monthly operating reports for the year 1999 were averaged to produce the table below 

which compares loads from the treatment plant with loads measured during the 186-day 

monitoring period, of this study, at the two monitoring stations (Drew Street and Kings 

Highway). Stevenson Creek at the location of the MWWTP discharge has a much higher 

capacity to assimilate pollution than do the upper, freshwater reaches of the creek, and 

Table 2.3-1 

Loads During Monitoring Period

Input Source 

Volume 

Discharged 

(ac-ft) 

BOD5 

(Pounds) 

TSS 

(Pounds) 

TN 

(Pounds) 

TP 

(Pounds) 

Base and Storm Flow 

(1) 3,170 101,199 157,406 11,542 3,084 

MWWTP 2,587 82,596 128,471 9,420 2,517 

Note: Loads measured (based on mean concentration of all samples, this study, and the overall 

flow) at the Spring Branch (King’s Highway) and Stevenson Creek (Drew Street) Station, 

May 2000 – November 2000
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these mass loading calculations are provided only to add perspective to overall watershed 

load estimates presented elsewhere in this report. 

Indirect evidence suggests that both the sanitary sewer system (i.e., crossconnections or inflow) and septic tanks may contribute to bacteria and nutrient levels in 

the Stevenson Creek Watershed. The MWWTP appears to receive a moderate increase in 

flow during the wet season. In addition, the locations and density of septic tank repair 

permits seem to coincide with the highest percent of human isolates found in the results 

of the fecal coliform sampling. 

A fourteen-year flow record (January 1985- January 2000) was reviewed for the 

MWWTP. During this time period the average daily flow during the wet season (JuneSeptember) was 7.06 MGD as compared to 6.65 MGD during the remaining eight months 

of the year. If this variation is due to increased rainfall during the wet season, then 

possible explanations for the increase are infiltration, inflow, or cross connections 

between the sanitary and storm systems. Anecdotal evidence of one possible infiltration 

or cross connection problem is provided by a resident who reported that a lift station on 

Sunset Point Road (just west of Stevenson Avenue) overflows during heavy rains 

“causing the creek to stink like sewage”. 

Pinellas County recently began keeping records of applications for septic tanks 

repairs. The locations of the septic tanks contained in this database were plotted (Figure 

2.3-3), and seem to suggest that septic tanks within the city are concentrated between 

Union Street and Palmetto Street. These locations are near City of Clearwater monitoring 

Station STC1 and STC2, which happen to be the two stations with the highest percent of 

human isolates in fecal coliform samples (refer to Appendix J and Figure 2.3-1). While 

this seems to implicate septic tanks as a source of fecal contamination, a direct “cause 

and effect” statement concerning the use of septic tanks in the Stevenson Creek 

Watershed cannot be made. Other factors, such as the downstream position of STC1 and 

STC2, may be the cause of the higher human-source fecal contamination that was 

observed - in other words, the origin of the human-sourced fecal contamination measured 

at STC1 and STC2 could potentially be located upstream of the septic tanks. 
Stevenson Creek Watershed Management Plan 

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Figure 2.3-3

Septic Tank Densities
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2.3.2 Monitoring Program 

A hydrologic and water quality monitoring program was implemented for the 

Stevenson Creek Watershed project. Two monitoring stations were installed – one 

station in Stevenson Creek (Stevenson Creek Station) just downstream of Drew Street and 

one station in Spring Branch (Spring Branch Station) just downstream of Kings Highway 

(Figure 2.3-4). 

Each station logged rainfall depth and channel stage at 15-minute intervals from 

May 21,2001 through November 23, 2000. Flow-weighted composite samples were 

collected for seven (7) separate storm events and grab samples were taken for six (6) base 

flow events at each station. Savannah Laboratories in Tampa analyzed the samples in 

accordance with their FDEP-approved quality assurance plan. One equipment blank for 

each station was collected and analyzed prior to the first storm-sampling event. 

Laboratory parameter included solids, oxygen demand, nutrients, metals and 

petroleum hydrocarbons. These parameters are more specifically described in Table 2.3-

2 along with their corresponding minimum detection limits. 

2.3.2.1 Monitored Basins 

The majority (65%) of the watershed was monitored. Figure 2.3-4 shows the areas 

that drain to each of the monitoring stations. These areas include a 2400-acre area 

draining to the Stevenson Creek Station and a 1700-acre area draining to the Spring 

Branch Station. The unmonitored portion of the basin is approximately 2200 acres. 

Both the Stevenson Creek and Spring Branch Stations are similar with respect to 

land use. The dominant land use is residential. The primary distinguishing factor is the 

presence of a larger amount of commercial land use in the Stevenson Creek Basin and a 

larger amount of high-density residential land use in the Spring Branch Basin. The Land 

uses in the unmonitored portion of the basin are similar to the monitored basins as shown 

in Figure 2.3-5 – shown as a doughnut graph to emphasize similarity. 
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Table 2.3-2 

Water Quality Sampling Parameters 

1

 Minimum Detection Limit 

Parameter 

MDL1 

(mg/l) 

Hardness as CaC03 3.3 

Petroleum Hydrocarbons 

Oil and Grease 5.0 

Total Recoverable Petroleum Hydrocarbons, TRPH 0.30 

Oxygen Demand 

Biochemical Oxygen Demand (5 Day), BOD5 2.0 

Chemical Oxygen Demand, COD 20 

Total Organic Carbon, TOC 1.0 

Solids 

Total Suspended Solids, TSS 5.0 

Total Dissolved Solids, TDS 5.0 

Metals 

Aluminum, Al 0.20 

Arsenic, As 0.010 

Cadmium, Cd 0.0050 

Chromium, Cr 0.010 

Copper, Cu 0.020 

Lead, Pb 0.0050 

Nickel, Ni 0.040 

Zinc, Zn 0.020 

Nutrients 

Ortho Phosphate, P 0.050 

Total Phosphorus, TP 0.10 

Ammonia, NH3 0.03 

Total Kjeldahl Nitrogen, TKN 0.20 

Nitrate + Nitrite, NO3, NO2 0.05 
Stevenson Creek Watershed Management Plan 

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Figure 2.3-4

Monitoring Stations Location and Coverage
Stevenson Creek Watershed Management Plan 

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Figure 2.3-5 

Land Use by Monitoring Station 

AgriculturalCommercialHigh Density ResideHighway/UtilityIndustrialInstitutionalLow Density ResideMedium Density ResOpen LandRecreationalUpland ForestWaterWetland ForestWetland Non-Forest

Unmonitored

Drew Street Station 

Spring Branch Station 
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2.3.2.2 Hydrologic Monitoring 

Hydrologic monitoring was conducted from May 21, 2000 through November 23, 

2000. Rainfall conditions preceding and during the monitoring period were, in general, 

drier than normal. Rainfall conditions leading up to and including the monitoring period 

as compared to normal conditions are shown on Figure 2.3-6. The monitoring period 

followed an extremely dry “dry season” (5.1 inches of rainfall were received October 

1999 to May 2000 at SWFWMD’s Site #15 rain gauge) with monthly rainfall conditions 

recovering to normal during the second month (June 2000) of monitoring. July 2000 was 

wetter than normal due chiefly to a large storm event that occurred on July 15 dropping 

7.7 inches at the Stevenson Creek Station and 5.7 inches at the Spring Branch Station. 

Drier-than-normal conditions returned after July. 

Towards the end of May 1999 it was discovered that the Stevenson Creek rain 

gage was receiving inputs from the Clearwater Country Club’s sprinkler system. The rain 

gauge was moved away from the influence of the sprinklers as far as possible; however, 

minor inputs were still received from the sprinklers. 

Translating the total measured flow during the monitoring period to a depth (flow 

volume divided by basin area), at the Stevenson Creek station 11.0 inches of rainfall 

appeared as flow the creek; likewise, 31.16 inches of rainfall at the Spring Branch Station 

resulted in 6.9 inches of flow. The remaining rainfall was lost to initial abstraction and 

evapotranspiration or became groundwater - later to appear as base flow of aquifer 

recharge. A simplified technique of base flow separation was applied to determine the 

relative magnitude of base flow. This technique uses the minimum daily flow during dry 

periods together with professional judgment to separate the flow into two componentsbase flow and storm event runoff. Overall hydrologic conditions for the monitoring 

period are listed in Table 2.3-3. Daily flow along with rainfall for the two monitoring 

stations is shown on Figures 2.3-7 and 2.3-9. Figures 2.3-8 and 2.3-10 provide a more 

detailed view for low flow conditions. 
Stevenson Creek Watershed Management Plan 

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 Figure 2.3-6 

Rainfall Conditions

0.05.0

10.015.020.025.0

Aug99 Sep- 99 Oct- 99 Nov- 99 Dec- 99 Jan- 00 Feb- 00 Mar- 00 Apr- 00 May- 00 Jun- 00 Jul- 00 Aug- 00 Sep- 00 Oct- 00 Nov- 00

Pinellas County Long-Term.Average for Month (SCS,1972)City of Clearwater(SWFWMD Pinellas CountySite #15)Stevenson Creek Station(refer to Section 2.3.2.2)Spring Branch Station

Pinellas County Long-Term. Average for Month (SCS,1972)

9.0 8.4 3.9 1.7 2.1 2.5 3.0 3.7 3.2 2.6 6.3 9.2 9.0 8.4 3.9 1.7

City of Clearwater (SWFWMD Pinellas County Site #15) 6.9 4.4 1.5 0.3 0.0 0.0 1.5 0.8 1.0 0.0 7.7 19.3 6.2 2.1 0.0 1.2Stevenson Creek Station (refer to Section 2.3.2.2) 1.54 9.70 17.95 4.46 7.93 1.68 2.34Spring Branch Station 0.00 6.74 14.22 3.92 5.20 0.17 0.91

Aug99 Sep- 99 Oct- 99 Nov- 99 Dec- 99 Jan- 00 Feb- 00 Mar- 00 Apr- 00 May- 00 Jun- 00 Jul-00 Aug- 00 Sep- 00 Oct- 00 Nov- 00
Stevenson Creek Watershed Management Plan 

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Table 2.3-3 

Overall Hydrologic Conditions at Monitoring Stations 

Watershed Item Quantity 

Percent of 

Rainfall 

Area (AC) 1,673.50 -- 

Rainfall Depth (in.) 31.16 100% 

Volume of Rain (AC-Ft.) 4,345.52 100% 

Total Flow (AC-Ft.) 960 22% 

Base Flow (AC-Ft.) 184 4% 

Spring Branch 

 

 

 

 

Storm Flow (AC-Ft.) 776 18% 

Area (AC) 2,415.50 

Rainfall Depth (in.) (1) 45.61 100% 

Volume of Rain (AC-Ft.) 9,181.91 100% 

Total Flow (AC-Ft.) 2210 24% 

Base Flow (AC-Ft.) 376 4% 

Stevenson Creek 

 

 

 

 

Storm Flow (AC-Ft.) 1834 20% 

Note 1 : Rainfall depth reflects inputs from Clearwater Country Club sprinkler systemrefer to Section 2.3.2.2. 
Stevenson Creek Watershed Management Plan 

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Figure 2.3-7 

Stevenson Creek Hydrologic Record 

0

200400600800

100012001400160018002000

May-00 Jun-00 Jul-00 Aug-00 Sep-00 Oct-00 

Date

Daily Flow (cfs)
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Figure 2.3-8 

Stevenson Creek Hydrologic Record 

Low Flow Detail 

05

101520253035

May-00 Jun-00 Jul-00 Aug-00 Sep-00 Oct-00 

Date

Daily Flow (cfs)
Stevenson Creek Watershed Management Plan 

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Figure 2.3-9 

Spring Branch Hydrologic Record 

0

50

100150200250300350400450

May-00 Jun-00 Jul-00 Aug-00 Sep-00 Oct-00 

Date

Daily Flow (cfs)
Stevenson Creek Watershed Management Plan 

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Figure 2.3-10 

Spring Branch Hydrologic Record 

Low Flow Detail 

05

101520253035

May-00 Jun-00 Jul-00 Aug-00 Sep-00 Oct-00 

Date

Daily Flow (cfs)
Stevenson Creek Watershed Management Plan 

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2.3.2.3 Water Quality 

Seven (7) storm event samples and six (6) base flow samples were collected at 

each monitoring station. The laboratory results are provided in Table 2.3-4. Violations of 

Class III water quality criteria occurred in a number of instances. Details concerning 

these exceedences as well as other information concerning the findings of the sampling 

program are described in the following section. 

2.3.3 Water Quality Characteristics 

Water quality in the Stevenson Creek Watershed is described in the following 

subsections. These descriptions include assessments of base flow and storm flow and 

identify probable sources of pollution. Water quality parameters measured during this 

project are compared to Florida water quality criteria (Chapter 62-302, Florida 

Administrative Code- referred to as water quality standards in this report), STORET 

database values (as published in the 2000 state Section 305(b) report), and comparable 

literature values, as appropriate. More specifically, comparisons are made with state 

water quality standard where numeric standards exists; otherwise, comparison is made 

with Florida averages as published in the 305(b) report (for base flow samples) or 

literature values (for stormwater runoff samples). Water quality indices are calculated for 

the base flow samples. 

The Florida Department of Environmental Protection (FDEP) recommends the 

use of a Water Quality Index (WQI) to summarize water quality conditions in rivers and 

streams (Hand et al. 1996). The WQI is based on six categories of water quality 

indicators (water clarity, dissolved oxygen, oxygen-demanding substances, bacteria, 

nutrients, and biological diversity). Several categories contain multiple constituents (e.g., 

total organic carbon and BOD5, within the category of oxygen-demanding substances). 

In such cases, data availability determines constituent(s) used in calculating the WQI. 

For each measured constituent, the raw data (e.g., monthly or quarterly observations) are 

converted to annual averages. The annual averages are then converted to percentiles, 
Stevenson Creek Watershed Management Plan 

Final Report 

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Table 2.3-4 – Laboratory Results 

 Metals Oxygen Dema

Date 

Log # 

Time 

Type 

Oil and Grease

Hardness 

as CaC03

Al 

As 

Cd 

Cr 

Cu 

Pb 

Ni 

Zn 

BOD5 

COD 

Ttl 

Stevenson Creek (Drew Street) 

"June 20, 2000" 61864-2 10:19 Base Flow #1 <5.0 140 <0.20 <0.010 <0.0050 <0.010 <0.020 <0.0050 <0.040 <0.020 5.9 30 1"June 30, 2000" 61983-1 14:15 Storm Event #1 <5.0 76 <0.20 <0.010 <0.0050 <0.010 <0.020 <0.0050 <0.040 <0.020 2.1 30 9

"July 12, 2000" 62071-2 12:08 Base Flow #2 <5.0 210 <0.20 <0.010 <0.0050 <0.010 <0.020 <0.0050 <0.040 <0.020 <2.0 37 1"July 20, 2000" 62194-1 12:30 Storm Event #2 <5.0 68 <.20 <0.01 <0.005 <0.01 <0.02 <0.005 <0.04 0.029 24 54 1"July 24, 2000" 62218-1 11:35 Storm Event #3 <5.0 71 <0.20 <0.010 <0.0050 <0.010 0.02 <0.0050 <0.040 <0.020 7.2 26 8"July 31, 2000" 62290-1 17:30 Storm Event #4 <5.0 59 0.69 <0.010 <0.0050 <0.010 <0.020 0.0071 <0.040 0.038 8.9 29 7

"August 3, 2000" 62336-2 14:34 Base Flow #3 <5.0 140 <0.20 <0.010 <0.0050 <0.010 <0.020 <0.0050 <0.040 <0.020 2.0 45 1

"August 23, 2000" 62526-1 10:27 Base Flow #4 <5.0 210 <0.20 <0.010 <0.0050 <0.010 <0.020 <0.0050 <0.0040 0.200 <2.0 <20 1

"September 13, 2000" 62731-1 13:45 Base Flow #5 <5.0 180 <0.20 <0.010 <0.0050 <0.010 <0.020 <0.0050 <0.040 <0.020 19.0 58 2"September 13, 2000" 62737-3 13:30 Storm Event #5 <5.0 140 <0.20 <0.010 <0.0050 <0.010 <0.020 <0.0050 <0.040 <0.020 <2.0 58 1"September 17, 2000" 62758-2 12:45 Storm Event #6 <5.0 89 0.62 <0.010 <0.0050 <0.010 <0.020 <0.0050 <0.040 0.036 60 38 3

"October 12, 2000" 62999-2 14:50 Base Flow #6 <5.0 190 0.33 <0.010 <0.0050 <0.010 <0.020 <0.0050 <0.040 0.022 <2.0 22 1

"November 15, 2000" 63376-2 13:30 Storm Event #7 <5.0 140 0.27 <0.010 <0.0050 <0.010 <0.020 0.0054 <0.040 0.066 14 93 2

Spring Branch (Kings Highway) 

"June 20, 2000" 61864-1 9:10 Base Flow #1 <5.0 150 0.25 <0.010 <0.0050 <0.010 <0.020 <0.0050 <0.040 <0.020 7.8 43 1"June 30, 2000" 61983-2 15:00 Storm Event #1 <5.0 64 <0.20 <0.010 <0.0050 <0.010 <0.020 <0.0050 <0.040 <0.020 3.3 <20 1

"July 12, 2000" 62071-1 11:17 Base Flow #2 <5.0 130 <0.20 <0.010 <0.0050 <0.010 <0.020 <0.0050 <0.040 <0.020 6.1 62 2"July 17, 2000" 62131-1 15:30 Storm Event #2 <5.0 34 0.44 <0.010 <0.0050 <0.010 <0.020 0.0130 <0.040 0.049 2.2 <20 4"July 20, 2000" 62194-2 13:25 Storm Event #3 <5.0 58 0.32 <0.01 <0.005 <0.01 <0.02 <0.005 <0.04 <0.020 14 43 1"July 31, 2000" 62290-2 18:45 Storm Event #4 <5.0 56 0.70 <0.010 <0.0050 <0.010 <0.020 0.0078 <0.040 0.037 25.0 58 2

"August 3, 2000" 62336-1 13:45 Base Flow #3 <5.0 130 0.65 <0.010 <0.0050 <0.010 <0.020 <0.0050 <0.040 0.024 <2.0 26 1

"August 23, 2000" 62526-2 12:05 Base Flow #4 <5.0 160 0.21 <0.010 <0.0050 <0.010 <0.020 <0.0050 <0.0040 0.200 98.0 38 2"August 23, 2000" 62526-3 11:45 Storm Event #5 <5.0 120 0.28 <0.010 <0.0050 <0.010 <0.020 <0.0050 <0.0040 0.250 52.0 <20 1

"September 13, 2000" 62731-2 15:00 Base Flow #5 <5.0 120 0.22 <0.010 <0.0050 <0.010 <0.020 <0.0050 <0.040 <0.020 12.0 54 1"September 17, 2000" 62758-1 11:00 Storm Event #6 <5.0 92 0.41 <0.10 <0.0050 <0.010 <0.020 0.0063 <0.040 0.037 12 36 1

"October 12, 2000" 62999-1 13:30 Base Flow #6 <5.0 220 0.39 <0.010 <0.0050 <0.010 <0.020 <0.0050 <0.040 <0.020 2.1 35 1

"November 15, 2000" 63376-1 12:00 Storm Event #7 <5.0 140 0.52 <0.010 <0.0050 <0.010 <0.020 0.0087 <0.040 0.100 21 110 3
Stevenson Creek Watershed Management Plan 

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using a database constructed by FDEP staff (Hand et al. 1990, 1996) using data from 

2,000 Florida stream monitoring locations. These percentile values, which range from 0 

(best quality) to 100 (poorest quality), are then averaged to generate the WQI. The final 

averaging process ignores water quality categories for which no data are available. The 

WQI calculated for a given stream-monitoring site can therefore represent the average of 

from 1 to 6 categories. Although the index can be calculated based on a single category, 

the use of additional categories provides greater reliability (Hand et al. 1990, 1996). 

FDEP recommends the following interpretation of WQI values, based on an analysis 

of Florida stream data and the US EPA National Profiles Water-Quality Index (Hand et 

al. 1996): 

0 < WQI < 45 = “good” water quality 

45 < WQI < 60 = “fair” water quality 

WQI > 60 = “poor” water quality. 

Data for four of the six possible water quality index categories was collected at 

the two sampling stations. Overall water quality at both stations is rated “poor” based on 

Table 2.3-5 

Water Quality Indices 

Category Subcategory Drew Street Spring Branch 

Water Clarity TSS 50.9 70.9 

Overall 57.1 64.9 

BOD 89.3 90 

Oxygen Demand COD 32.8 46.2 

TOC 49.2 58.6 

Overall 66.1 62.9 

Total Nitrogen 54 61.8 

Nitrate + Nitrite 70.2 47.7 

Nutrients 

Total Phosphorous 74.2 79.3 

Bacteria Fecal Coliform 90 90 

Overall 66.0 72.2 
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the average of base flow samples taken during this monitoring program with quality at 

the Spring Branch station rated moderately poorer than at the Drew Street station Table 

(2.3-5). 

2.3.3.1 Petroleum Hydrocarbons 

Petroleum hydrocarbons include oil and grease; the “BTEX” compounds: 

benzene, toluene, ethyl benzene, and xylene; as well as other polynuclear aromatic 

hydrocarbons (PAHs). The most common sources of petroleum hydrocarbons are 

associated with vehicle usage. These sources include parking lots and roads, leaking 

storage tanks, automobile emissions, and improper or careless handling or disposal of oil; 

therefore, petroleum hydrocarbons are typically concentrated along transportation routes. 

Petroleum hydrocarbons are acutely toxic at relatively low concentrations. 

For this study, oil and grease was used as an “indicator” pollutant for petroleum 

hydrocarbons. The sampling plan specified that if oil and grease concentrations above 5.0 

mg/l were detected, then tests would also be conducted for petroleum hydrocarbons. Oil 

and grease was not detected; therefore, tests for petroleum hydrocarbons were not 

conducted. While petroleum hydrocarbons are certainly present in any urban area, they 

do not appear to be a significant concern in the portion of the Stevenson Creek Watershed 

that was monitored. 

2.3.3.2 Oxygen Demand 

Oxygen-demanding substances were measured by testing for Biochemical 

Oxygen Demand (BOD), Chemical Oxygen Demand (COD), and Total Organic Carbon 

(TOC). Maintaining appropriate levels of dissolved oxygen is one of the most important 

considerations for the protection of fish and aquatic life. The state standard for dissolved 

oxygen in Class III waters is 5.0 mg/l or greater. 

The direct impact of storm water runoff on dissolved oxygen conditions in 

receiving waters is normally not as important as the secondary impacts. Secondary 

impacts of low dissolved oxygen conditions include nutrient enrichment, eutrophication, 

and increased sediment oxygen demand. 
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Table 2.3-6, Base Flow Oxygen Demand 

Date BOD5 

(mg/l) 

COD 

(mg/l)

TOC

(mg/l)

Stevenson Creek - Drew Street 

June 20, 2000 5.9 30 15

July 12, 2000 <2.0 37 12

August 3, 2000 2 45 11

August 23, 2000 <2.0 <20 11

September 13, 2000 19 58 24

October 12, 2000 <2.0 22 10

Mean 5.0 34 14

WQI 89.3 32.8 49.2

Spring Branch - Kings Highway 

June 20, 2000 7.8 43 19

July 12, 2000 6.1 62 20

August 3, 2000 <2.0 26 13

August 23, 2000 98 38 21

September 13, 2000 12 54 18

October 12, 2000 2.1 35 11

Mean 5.8 43 17

WQI 90 46.2 58.6

Frequency of Exceedance in Florida Streams 

STORET-10% 0.8 16 5

Median 1.5 46 14

STORET-90% 5.1 146 37

Base flow sampling results values (Table 2.3-6) in comparison to Florida 

averages), and storm event sampling results (Table 2.3-7) in comparison with Nationwide 

Urban Runoff Program (NURP) data from the Tampa Bay Sampling sites are provided. 

Three laboratory measurements 

appear to be in error and, 

therefore, were not used. The 

laboratory is unable to 

specifically identify the source 

of the error; however, the error 

may have been caused by a 

standard solution that was 

more concentrated than 

specified by the test. These 

erroneous measurements 

include the base flow sample 

taken on August 23, 2000 at 

the Kings Highway Station, the 

storm event sample that was 

composited on the same day 

and location, and the 

September 17, 2000 storm 

event sample taken at Drew Street. These readings are suspect due to the much lower 

COD measurements taken on the same sample. COD should normally be higher than 

BOD5, and no case should BOD5 be significantly greater than COD. This is because BOD 

measures the actual oxygen consumption of microorganisms, and COD measures the 

amount of oxidant required to oxidize the available organic matter; therefore, a BOD that 

is higher than a COD implies that more organic material was consumed than was 

available for consumption. 

BOD was still high relative to typical Florida streams even without considering 

the erroneous measurements. Moderately higher BOD concentrations were present at the 
Stevenson Creek Watershed Management Plan 

Final Report 

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Table 2.3-7 

Storm Event Oxygen Demand 

 Date BOD5 

(mg/l) 

COD

(mg/l)

TOC 

(mg/l)

Drew Street 

June 30, 2000 2.1 30 9.3 

July 20, 2000 24 54 15 

July 24, 2000 7.2 26 8.2 

July 31, 2000 8.9 29 7.4 

September 13, 2000 <2.0 58 11 

September 17, 2000 60i 38 30 

November 15, 2000 14 93 27 

EMC 12.19 47.3 15.7

Kings Highway 

June 30, 2000 3.3 <20 10 

July 17, 2000 2.2 <20 4.6 

July 20, 2000 14 43 12 

July 31, 2000 25 58 23 

August 23, 2000 521 <20 15 

September 17, 2000 12 36 10 

November 15, 2000 21 110 37 

EMC 15.35 43.5 16.5

Tampa Bay NURP 

Minimum 0.7 5 0 

Mean 5.4 58 14 

maximum 28 210 88 

 

i

 Erroneous measurement – not used 

 
Stevenson Creek Watershed Management Plan 

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Spring Branch station than were observed at the Stevenson Creek station. COD and BOD 

were near the state average. 

2.3.2.3 Solids 

Solids are one of the most common contaminants found in urban storm water. Solids 

originate from many sources including the erosion of pervious surfaces and dust, litter 

and other particles deposited on land surfaces from human activities and the atmosphere. 

Stream bank and streambed erosion also appears to be a major source of solids in the 

Stevenson Creek Watershed. 

Solids contribute to water quality, habitat and maintenance problems in Stevenson 

Creek Watershed. Elevated levels of solids increase turbidity, reduce the depth of light 

penetration within the water column, and limit the growth of desirable aquatic plants. 

Solids that settle out as bottom deposits and can alter habitat for fish and bottom-dwelling 

organisms. Solids also provide a medium for the accumulation, transport and storage of 

other pollutants including nutrients and metals. Sediment- bound pollutants interact with 

the water column through cycles of deposition, re-suspension, and re-deposition. 

Suspended solids (TSS) concentrations in base flow were high at the Spring 

Branch station and near the Florida average at the Drew Street station. As expected, 

suspended solids concentrations increased substantially during storm events with the 

Spring Branch station experiencing higher concentrations than the Drew Street station. 

Results are provided on Tables 2.3-8 and 2.3-9. 

2.3.2.4 Metals 

Metals detected in the Stevenson Creek Watershed include aluminum, lead, and 

zinc. This finding is typical. Aluminum is the second most abundant naturally occurring 

metal and lead and zinc are the most commonly detected metals in stormwater runoff1. 

Likely sources of the lead and zinc present in the Stevenson Creek Watershed include 

vehicle usage, atmospheric deposition, and erosion. A major finding of the NURP study 

is as follows: 

 

1 Lead and zinc were detected in 94% of NURP samples. 
Stevenson Creek Watershed Management Plan 

Final Report 

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Table 2.3-8 

Base Flow Solids 

Date Total Suspended 

Solids (TSS, mg/l) 

Total Dissolved Solids 

(TDS, mg/l) 

Stevenson Creek 

June 20, 2000 6.8 200 

July 12, 2000 <5.0 350 

August 3, 2000 8.4 210 

August 23, 2000 <5.0 300 

September 13, 2000 <5.0 240 

October 12, 2000 18 300 

Mean 6.78 267 

WQI 50.9 - 

Spring Branch 

June 20, 2000 16 270 

July 12, 2000 15 240 

August 3, 2000 19 240 

August 23, 2000 7.2 220 

September 13, 2000 9.2 220 

October 12, 2000 10 330 

Mean 12.73 253 

WQI 70.9 - 

Frequency of Exceedance in Florida Streams 

STORET-10% 2 - 

Median 6.5 - 

STORET-90% 26.5 - 
Stevenson Creek Watershed Management Plan 

Final Report 

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Table 2.3-9 

Storm Event Solids 

Date Total Suspended Solids 

(TSS, mg/l)

Total Dissolved Solids 

(TDS, mg/l)

Stevenson Creek 

June 30, 2000 <5.0 130 

July 20, 2000 15 110 

July 24, 2000 6 94 

July 31, 2000 30 86 

September 13, 2000 6 220 

September 17, 2000 26 140 

November 15, 2000 26 240 

EMC 18.3 147 

Spring Branch 

June 30, 2000 8.8 100 

July 17, 2000 39 41 

July 20, 2000 14 120 

July 31, 2000 23 200 

August 23, 2000 21 170 

September 17, 2000 21 120 

November 15, 2000 44 370 

EMC 25.13 168 

NURP Mixed Urban - 

Mean 

67 - 
Stevenson Creek Watershed Management Plan 

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Heavy metals (especially copper, lead and zinc) are by far the most 

prevalent priority pollutant constituents found in urban runoff. 

End-of-pipe concentrations exceed EPA ambient water quality 

criteria and drinking water standards in many instances. Some of 

the metals are present often enough and in high enough 

concentrations to be potential threats to beneficial uses. 

Metals can be toxic to aquatic life, and lead and zinc concentrations exceeding 

state standards were often measured during the monitoring program- more often in storm 

flow and more often at Spring Branch. Metals concentration for both of the monitoring 

stations are shown on Table 2.3-10 along with comparison to state water quality criteria 

and NURP data. The standards for lead and zinc are hardness-dependant, and the 

standard for lead was often less than the detection limit. 

2.3.3.5 Nutrients 

Nitrogen and phosphorus are the principal nutrients of concern in urban storm 

water. The major sources of nitrogen and phosphorus in the Stevenson Creek Watershed 

are likely associated with landscape runoff (fertilizers and organic debris) and 

atmospheric deposition. Improperly functioning septic tank systems and animal waste 

may also be an important source. 

There are a number of parameters used to measure the various forms of nitrogen. 

Ammonia (NH3) nitrogen is the nitrogen form that is usually the most readily toxic to 

aquatic life. Nitrate (NO3) and nitrite (NO2) are the inorganic fractions of nitrogen. Very 

little nitrite is usually found in storm water. Total Kjeldahl nitrogen (TKN) measures the 

organic and ammonia nitrogen forms. The organic fraction is determined by subtracting 

the NH3 from the TKN. 

Total phosphorus measures the total amount of phosphorus in both the organic 

and inorganic forms. Ortho-phosphate measures phosphorus that is most immediately 

biologically available. Most of the soluble phosphorus in storm water is usually present in 

the ortho-phosphate form. 
Stevenson Creek Watershed Management Plan 

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 Table 2.3-10 

Metals 

Aluminum1 Lead Zinc 

Date Type of Flow Measurement 

(1) 

Measurement Class III-Fresh 

Standard 

Measurement Class III-Fresh 

Standard 

Stevenson Creek 

June 20, 2000 Base Flow #1 <0.20 <0.0050 0.00488 <0.020 0.14096

July 12, 2000 Base Flow #2 <0.20 <0.0050 0.00818 <0.020 0.19874

August 3, 2000 Base Flow #3 <0.20 <0.0050 0.00488 <0.020 0.14096

August 23, 2000 Base Flow #4 <0.20 <0.0050 0.00818 0.200 0.19874

September 13, 2000 Base Flow #5 <0.20 <0.0050 0.00672 <0.020 0.17441

October 12, 2000 Base Flow #6 0.33 <0.0050 0.00720 0.022 0.18258

 

June 30, 2000 Storm Event #1 <0.20 <0.0050 0.00224 <0.020 0.08400

July 20, 2000 Storm Event #2 <.20 <0.0050 0.00195 0.029 0.07645

July 24, 2000 Storm Event #3 <0.20 <0.0050 0.00206 <0.020 0.07929

July 31, 2000 Storm Event #4 0.69 0.0071 0.00163 0.038 0.06778

September 13, 2000 Storm Event #5 <0.20 <0.0050 0.00488 <0.020 0.14096

September 17, 2000 Storm Event #6 0.62 <0.0050 0.00274 0.036 0.09603

November 15, 2000 Storm Event #7 0.27 0.0054 0.00488 0.066 0.14096

Spring Branch 

June 20, 2000 Base Flow #1 0.25 <0.0050 0.00533 <0.020 0.14944

July 12, 2000 Base Flow #2 <0.20 <0.0050 0.00444 <0.020 0.13238

August 3, 2000 Base Flow #3 0.65 <0.0050 0.00444 0.024 0.13238

August 23, 2000 Base Flow #4 0.21 <0.0050 0.00579 0.200 0.15784

September 13, 2000 Base Flow #5 0.22 <0.0050 0.00401 <0.020 0.12370

October 12, 2000 Base Flow #6 0.39 <0.0050 0.00868 <0.020 0.20673

 

June 30, 2000 Storm Event #1 <0.20 <0.0050 0.00180 <0.020 0.07262

July 17, 2000 Storm Event #2 0.44 0.0130 0.00081 0.049 0.04249

July 20, 2000 Storm Event #3 0.32 <0.005 0.00159 <0.020 0.06681

July 31, 2000 Storm Event #4 0.70 0.0078 0.00152 0.037 0.06485

August 23, 2000 Storm Event #5 0.28 <0.0050 0.00401 0.250 0.12370

September 17, 2000 Storm Event #6 0.41 0.0063 0.00286 0.037 0.09876

November 15, 2000 Storm Event #7 0.52 0.0087 0.00488 0.100 0.14096

NURP -Nationwide Mean 

Residential 

Mixed Urban 

Commercial 

0.144 

0.114 

0.104 

0.135 

0.154 

0.226 

Tampa Bay NURP 

Minimum 

Mean 

Maximum 

0.012 

0.058 

0.320 

0.020 

0.097 

0.300 

 

1

 There is no aluminum standard for freshwater. The aluminum standard for Class III marine waters is 1.5 

mg/l. 
Stevenson Creek Watershed Management Plan 

Final Report 

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The degree to which nitrogen and phosphorus are present can determine the 

trophic status and amount of algal biomass produced. Excess nutrients increase biological 

productivity. The major impact associated with nutrient over-enrichment is excessive 

growth of algae that leads to nuisance algal blooms and eutrophic conditions. A 

secondary impact is the residual negative effect of decomposing algae in the form of 

sediment oxygen demand that depletes dissolved oxygen concentrations, particularly in 

bottom waters. 

Nutrient concentrations measured during the monitoring period are presented on 

Tables 2.3-11 and 2.3-12 in comparison with STORET and NURP data. Nutrient 

concentrations do not appear to increase with storm event flow; however, since storms 

produce high flows the resulting increases in masses are significant. 

With respect to nutrients, the Spring Branch station had slightly worse water 

quality than did the Drew Street station with the primary difference being nitrogen forms 

at each of the station. Higher-than-average levels of inorganic nitrogen levels were 

recorded at the Drew Street station and higher-than-average organic nitrogen levels were 

recorded at the Spring Branch station. Ammonia nitrogen often exceeded the state 

standard during the monitoring period at both stations. 

2.3.3.6 Bacteria 

Fecal contamination is one of the most severe water quality issues in Stevenson 

Creek. The magnitude and frequency of fecal counts reported in past monitoring (City of 

Clearwater 1992-1995)) as well as this current program are very high. The state threshold 

for ranking a stream in the top ten percent of Florida’s worst water quality with respect to 

fecal coliforms is 960 colony-forming units (CFU) per 100ml. The highest count during 

this study was 20,000 and previous studies have recorded similarly high counts. The state 

standard for fecal coliforms in Class III waters is 800 counts per 100 ml. 

 The University of South Florida Department of Biology accomplished sampling 

for fecal contamination under a separate monitoring program. A bacterial source tracking 
Stevenson Creek Watershed Management Plan 

Final Report 

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Table 2.3-11 

Base Flow Nutrients 

Date 

Ortho 

Phosphate 

(mg/l) 

Total 

Phosphorus 

(mg/l) 

Total 

Kjeldahl 

Nitrogen 

(mg/l) 

Nitrate 

+ Nitrite 

(mg/l) 

Organic-N 

(mg/l) 

Ammonia 

(mg/l) 

Total 

Nitrogen 

(mg/l) 

Stevenson Creek - Drew Street Station 

June 20, 2000 0.45 0.56 1.1 <0.050 1.012 0.088 1.1

July 12, 2000 0.37 0.36 1.8 <0.050 1.66 0.14 1.8

August 3, 2000 0.2 0.27 0.81 0.18 0.719 0.091 0.99

August 23, 2000 0.17 0.21 0.82 0.27 0.732 0.088 1.09

September 13, 2000 0.12 0.21 0.89 0.44 0.74 0.15 1.33

October 12, 2000 0.18 0.38 1.1 0.27 1.062 0.038 1.37

Mean 0.25 0.33 1.09 0.20 0.988 0.10 1.28

WQI - 74.2 - 70.2 - - 54.0

Spring Branch - Kings Highway Station 

June 20, 2000 0.56 0.76 1.9 <0.050 1.79 0.11 1.9

July 12, 2000 0.64 0.73 2.1 <0.050 2.1 <0.030 2.1

August 3, 2000 0.26 0.46 0.94 0.36 0.873 0.067 1.3

August 23, 2000 0.23 0.3 1.1 0.068 1.003 0.097 1.168

September 13, 2000 0.17 0.27 1.2 <0.050 1.154 0.046 1.2

October 12, 2000 0.067 0.15 0.89 0.052 0.77 0.12 0.942

Mean 0.32 0.45 1.36 0.093 1.28 0.088 1.44

WQI - 79.3 - 47.7 - - 61.8

Frequency of Exceedence in Florida Streams 

STORET-10% 0.02 - - 0.01 - - 0.5 

Median 0.09 -- - 0.1 - - 1.2 

STORET-90% 0.89 - - 0.64 - - 2.7 

State Class III Standard - - - - <0.02 
Stevenson Creek Watershed Management Plan 

Final Report 

2.3-33 

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Table 2.3-12 

Storm Event Nutrients 

Date 

Ortho 

Phosphate

(mg/l) 

Total 

Phosphorus

(mg/l) 

Total 

Kjeldahl 

Nitrogen

(mg/l) 

Nitrate + 

Nitrite 

(mg/l) 

Organic-N 

(mg/l) 

Ammonia

(mg/l) 

Total 

Nitrogen

(mg/l) 

Stevenson Creek - Drew Street Station 

June 30, 2000 0.17 0.22 0.66 <0.050 0.601 0.059 0.66 

July 20, 2000 0.1 0.17 0.78 <0.050 0.66 0.12 0.78 

July 24, 2000 0.11 0.16 0.88 <0.050 0.59 0.29 0.88 

July 31, 2000 0.14 0.3 0.65 0.51 0.592 0.058 1.16 

September 13, 2000 0.2 0.26 0.87 0.55 0.833 0.037 1.42 

September 17, 2000 0.24 0.49 1.2 0.23 1.146 0.054 1.43 

November 15, 2000 0.34 0.57 1.6 0.34 1.569 0.031 1.94 

EMC 0.19 0.31 0.95 0.36 0.86 0.09 1.31 

Spring Branch - Kings Highway Station 

June 30, 2000 0.29 0.33 0.8 0.055 0.721 0.079 0.855

July 17, 2000 0.21 0.45 1.4 <0.050 1.25 0.15 1.4 

July 20, 2000 0.2 0.27 0.93 <0.050 0.82 0.11 0.93 

July 31, 2000 0.22 0.35 0.95 0.18 0.79 0.16 1.13 

August 23, 2000 0.19 0.36 1.4 0.32 1.316 0.084 1.72 

September 17, 2000 0.14 0.41 0.81 0.25 0.7 0.11 1.06 

November 15, 2000 0.6 1 2.8 <0.050 2.722 0.078 2.8 

EMC 0.26 0.45 1.30 0.14 1.19 0.11 1.41 

State Class III Standard - - - - <0.02 - 

NURP -Nationwide Mean 

Residential 0.143 0.383 1.9 0.736 2.636

Mixed Urban 0.056 0.263 1.288 0.558 1.846

Commercial 0.08 0.201 1.179 0.572 1.751

Tampa Bay NURP 

Minimum 0.02 0.02 0.01 0.18 0.04 0.52 

Mean 0.09 0.23 0.34 1.1 0.4 2.0 

Maximum 0.22 1.1 0.81 2.7 1.5 3.2 
Stevenson Creek Watershed Management Plan 

Final Report 

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(BST) method was applied to classify the source of fecal matter into three categories – 

human, dog, and wild animal. The report, which documents the results and findings, is 

provided in Appendix J. 

The source of most of the fecal contamination was identified as wild animal; 

however, significant human-sourced contamination was also discovered. The presence of 

fecal coliform bacteria from human sources was particularly evident at sample site STC1 

(near the confluence of Spring Branch with the main branch), a site that is surrounded by 

onsite wastewater treatment and disposal systems (OSTDS). STC2, on Hammond 

Branch, was also impacted frequently by indicator bacteria from human sources, and is 

downstream from another cluster of residences serviced by OSTDS. 

Some percent of isolates from other sources will misclassify as human isolatesthis is true of all BST methodologies. The rate of misclassification of isolates into the 

human category can be used to develop a cut-off point for significant levels of human 

isolates. In this database, about 20% of wild animal isolates are misclassified as human, 

and wild animal isolates have the highest rate of misclassification as human of all 

sources. The conservative rate of 25% is used as the cut-off point for identification of a 

significant percentage of isolates from human sources in any sample. 

Valerie J. Harwood, a professor at the University of South Florida who conducted 

the BST study for this project, provided the following description of the significance of 

fecal coliform in surface waters. 

The goal of bacteriological water quality testing is, in large part, to 

identify water that contains human pathogens in order to protect public health. 

Ideally, water quality testing would reliably identify public health threats, while 

allowing full use of waters that do not constitute a health threat. This goal has 

been elusive, in part because of the limitations of the methods we use. It is 

difficult, time-consuming and expensive to directly quantify disease-causing 

bacteria and viruses, and virtually impossible to test for all possible pathogens 

in a water sample. Thus, we quantify indicator bacteria, whose presence moreor-less reflects the probability that there are pathogens in the water. A major 

problem with the fecal coliform indicator is that it is a poor predictor of some 

human pathogens, particularly enteric viruses, but can also be present in waters 

where there are few or no viral, bacterial or protozoan pathogens. The same 

problem exists when E. coli, a member of the fecal coliform group, or 

Enterococcus, a different bacterial group, are used as indicator organisms for 

water quality. 
Stevenson Creek Watershed Management Plan 

Final Report 

2.3-35 

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One of the major reasons that fecal coliforms are inadequate indicators 

is that they are present in the gastrointestinal tract of all warm-blooded animals 

and some cold-blooded animals. Some animal feces, i.e. those of humans, cattle, 

and swine, have a higher probability of containing human pathogens than the 

feces of most other species, therefore many water quality experts would place 

contamination from these animals in a “high risk” group. Human feces are 

considered particularly dangerous because of the human-specific viruses 

transmitted exclusively by human sources. Very low levels of fecal indicator 

bacteria from a high-risk animal group indicate a greater potential health 

hazard than higher levels of indicator bacteria from a low risk animal group. 

There is, however, no testing method approved by regulatory agencies such as 

the EPA that can be used to determine the source (i.e. cow, human, dog) of fecal 

indicator bacteria. Such a method would allow much more accurate risk 

assessment than we can achieve with standard testing methods. It would also 

allow regulatory agencies to more effectively identify and eliminate the source 

of bacterial contamination to natural waters, and would contribute greatly to 

the accuracy of total maximum daily load (TMDL) models. 

Due to the history of high fecal coliform numbers in the urban 

Stevenson Creek watershed in Clearwater, Florida, the City of Clearwater 

funded a cutting-edge study of the sources of bacteria in this area. Based on 

land use patterns in the waters studied, one could predict significant fecal inputs 

from wild animals, particularly birds and raccoons, and from dogs. Other major 

candidates for fecal coliform contamination in this watershed include onsite 

wastewater treatment and disposal systems (OSTDS) whose drainfields are not 

functioning properly, or which have been bypassed. While limited steps can be 

taken to reduce the amount of dog wastes that enter surface waters, runoff from 

yards and other surfaces inevitably transports such waste to waters. 

Contributions from wild animal feces to the watershed are, if anything, more 

difficult to control than contributions from dogs. It is, however, possible to 

control the impact of human waste on water quality. Improvements in central 

sewer systems and OSTDS installations have greatly improved water quality 

overall in the U.S. since the implementation of the Clean Water Act in 1970. 

However, continued degradation of water quality in many surface waters, 

combined with heightened awareness of the dangers of waterborne pathogens, 

has led to renewed efforts to understand and mitigate the sources of microbial 

pollution in natural waters. 

2.3.4 Nonpoint Source Loading Model 

A nonpoint source loading model was prepared to estimate pollutant loads from 

Stevenson Creek Watershed. This model uses the EPA Simple Method, which is an 

event mean concentration (EMC) approach. In this approach, mass loads are calculated as 

the product of the EMC and the stormwater runoff volume. The stormwater runoff 

volume is estimated as the fraction of rainfall appearing as runoff multiplied by the basin 

area. The EMC is constant; thus, this method is also refereed to as the “constant 

concentration” method. 
Stevenson Creek Watershed Management Plan 

Final Report 

2.3-36 

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This loading model is intended to serve as an estimate. The water quality 

estimating procedures used for this project are very simple, yet water quality estimations 

by any means are not precise. Dr. Wayne Huber in the EPA SWMM User’s Manual 

expressed this fact very well. 

Simulation of urban runoff quality is a very inexact science if it can 

even be called such. Very large uncertainties arise both in the 

representation of the physical, chemical and biological processes 

and in the acquisition of data and parameters for model algorithms 

Nevertheless, the loading estimates for the Stevenson Creek Watershed presented 

herein represent a reasonable estimate that can be used to guide management actions. 

The flow and water quality data collected for this project (Section 2.3.2) were 

used along with soils and land use coverage information to develop the runoff 

coefficients (Section 2.3.4.1) and EMCs (2.3.4.2); subsequently, this information was 

used in combination with an existing stormwater treatment evaluation to determine mass 

loads and loading rates. Additional details concerning the individual elements of the 

analysis are contained in the following subsections. 

2.3.4.1 Runoff Coefficients 

Runoff coefficients are based on soils and landuse and represent the fraction of 

rainfall appearing as runoff. The relationship between rainfall and runoff is, however, not 

truly linear; thus, each unique rainfall event will have a different runoff coefficient for a 

given basin. During the dry season less runoff occurs because more water is required to 

wet the ground surface, and infiltration occurs at a faster rate. This is because there is less 

soil moisture. Runoff will occur on a pervious surface only if the rainfall rate exceeds the 

soil infiltration rate. Infiltration rates are lower when the ground is wet and become equal 

to zero when the ground is saturated. 

The runoff coefficients developed for the Stevenson Creek Watershed are 

intended to represent the fraction of rainfall appearing as runoff for an average year. The 

vast majority of published runoff coefficients are intended for use in the Rational 

Formula for peak discharge rate estimation as opposed to runoff volume estimation. 
Stevenson Creek Watershed Management Plan 

Final Report 

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While, by definition, there is no difference between these two types of runoff coefficients 

(peak rate or flow volume), runoff coefficients used in the Rational formula generally 

have factors of safety built in. For this reason the runoff coefficients developed for the 

Stevenson Creek Watershed are generally lower than published runoff coefficients. 

The overall runoff coefficients for the monitored basin are 0.29 for the Stevenson 

Creek Station and 0.27 for the Spring Branch Station. These overall coefficients were 

calculated using the overall storm event runoff coefficients (Table 2.3-3) for the 

monitoring period and the overall runoff coefficient for a September 17, 2000 event. 

Assuming that, in an average year, 60% of the total rainfall depth occurs during the four 

wet months (June, July, August, and September), the overall coefficients were weighted 

60-40 between the “typical wet season event” (September 17, 2000) and the overall 

monitoring period coefficients. Runoff coefficients developed for this project are shown 

in Table 2.3-13. 

Runoff coefficients for each unique soil-landuse combination were then 

developed. The weighted average of these coefficients match the calculated overall runoff 

coefficients which, in turn, are based on the monitoring data; thus, the runoff coefficients 

are, in a sense, calibrated. Obviously, runoff coefficients for soils/landuse combinations 

that are well represented in the monitored basins will be more accurate than combinations 

that are not well represented. 

2.3.4.2 Event Mean Concentrations 

An EMC is the concentration that has a 50% probability of being exceeded during 

a storm event; thus, over the course of time, half of the storms will produce 

concentrations higher than the EMC and half of the storms will produce concentrations 

lower than the EMC. 

Landuse-based EMCs were developed based on a two-step process. In the first 

step, in-stream EMCs and runoff coefficients were developed using the monitoring data; 
Stevenson Creek Watershed Management Plan 

Final Report 

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Table 2.3-13 

Stevenson Creek Watershed Runoff Coefficients 

Landuse Soil RC

A 0.075

B/D 0.104

C 0.133

D 0.154

UND 0.098

A 0.421

B/D 0.439

C 0.457

D 0.469

W 1.000

A 0.421

B 0.439

B/D 0.448

C 0.457

D 0.469

W 1.000

A 0.347

B/D 0.367

C 0.387

D 0.402

UND 0.363

W 1.000

A 0.347

B/D 0.367

C 0.387

D 0.402

A 0.298

B/D 0.319

C 0.341

D 0.357

W 1.000

A 0.100

B/D 0.128

C 0.156

D 0.177

W 1.000

A 0.149

B 0.176

B/D 0.189

C 0.202

D 0.222

UND 0.170

W 1.000

Medium Density Residential

Low Density Residential

Commercial

Agricultural

Institutional

Industrial

Highway/Utility

High Density Residential

Landuse Soil RC

A 0.075

B 0.104

B/D 0.119

C 0.133

D 0.154

W 1.000

A 0.124

B/D 0.152

C 0.179

D 0.199

UND 0.146

W 1.000

A 0.050

B/D 0.080

C 0.110

D 0.132

W 1.000

A 1.000

B 1.000

B/D 1.000

C 1.000

D 1.000

W 1.000

B/D 0.046

C 0.110

D 0.132

W 1.000

B/D 0.046

C 0.110

D 0.132

W 1.000

Wetland Non-Forested

Wetland Forest

Water

Upland Forest

Recreational

Open Land
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Table 2.3-14 

In-Stream EMCs 

Parameter

Spring Branch 

EMC (mg/l)

Stevenson Creek 

EMC (mg/l)

Pb 0.006 0.004

Zn 0.079 0.030

BOD5 15.350 12.190

TSS 25.129 18.260

TP 0.452 0.310

TN 1.412 1.310

subsequently, the in-stream EMCs were used to develop landuse-based EMCs. The 

process used to develop EMCs for this project is described in the following three 

subsections. 

2.3.4.2.1 In-stream EMCs 

Statistical analyses were conducted using the storm event monitoring data to 

develop the in-stream EMCs. EMCs are 

commonly assumed to follow a lognormal 

distribution. A normal distribution is the 

familiar bell-shaped curve. The lognormal 

distribution is similarly shaped; however, 

it is the natural log of the data that is 

distributed symmetrically about the mean 

rather than the data itself. Studies1 have 

shown that a lognormal distribution best represents EMCs. Lognormal distributions are 

used for many applications when the sample size is relatively small and variations 

between individual measurements are extreme. As the sample size increases the mean 

calculated using a lognormal distribution will approach the arithmetic mean. 

In-stream EMCs for the Stevenson Creek and Spring Branch Stations are shown 

in Table 2.3-14. 

2.3.4.2.2 Existing Stormwater Runoff Treatment 

Exiting stormwater treatment areas are present in the Stevenson Creek Watershed. 

These treatment areas consist of permitted dry retention and wet detention pond as well 

as natural lakes and man-made depressional storage areas. The general locations of these 

treatment areas are shown on Figure 2.3-11 inside the subbasin in which they are 

contained. Assumptions used in this evaluation of existing treatment are as follows: 

 
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Figure 2.3-11

Existing Stormwater Treatment Areas
Stevenson Creek Watershed Management Plan 

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• Treatment depth. Permitted stormwater treatment areas are 

assumed to provide one inch of treatment for wet detention 

areas and one-half inch of treatment for dry retention areas. 

This is consistent with SWFWMD and City of Clearwater 

design criteria for stormwater treatment areas. Lakes and 

other “natural” BMPs are assumed to provide a maximum 

treatment depth of one inch adjusted downward based on 

the ratio of the BMP area to the tributary basin. This results 

in a treatment depth range of 0.01 to 1 inch. BMP 

efficiencies equal to one-half those for wet detention were 

applied and adjusted by the estimated treatment depth. 

• Treatment Coverage. Water is treated only once. In other 

words water from a BMP (BMP A) which drains to a 

downstream basin that also contains a BMP (BMP B) is not 

treated again in BMP B. This assumption simplified the 

analysis and is rational for a number of reasons. First, most 

permitted BMPs do not receive runoff from offsite basins 

and, instead, drain directly to the primary storm sewer 

system. Second, BMPs in-line to the main storm sewer 

system will fill with water from the nearest areas first. 

Subsequent flows will either bypass treatment or reduce the 

treatment efficiency; therefore, it is reasonable to assume 

that these flows will not be treated. Treatment coverage is 

illustrated on Figure 2.3-12. 

BMP efficiencies (Table 2.3-15) are based on literature values and adjusted for 

agreement with measurements taken during the monitoring program. 

Table 2.3-15 

BMP Maximum Efficiencies 

Parameter Wet Detention Dry Retention

Natural 

Treatment

Pb 75% 80% 0.38

Zn 60% 80% 0.3

BOD5 50% 80% 0.25

TSS 75% 80% 0.38

TP 60% 80% 0.3

TN 30% 80% 0.15
Stevenson Creek Watershed Management Plan 

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Figure 2.3-12

Treatment Coverage 
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2.3.4.2.3 Landuse-Based EMCs 

Landuse-based EMCs were developed based on the measured in-stream EMCs. 

The process used to develop EMCs was to vary estimates of landuse-based EMCs until 

agreement with recorded data as well as agreement between the two monitoring stations 

was achieved. This process was performed mindful of literature values of EMCs so that 

individual EMC values were not assigned outside of a reasonable range. 

The results agree well with the recorded data at the Stevenson Creek Station; 

however, lead, zinc, BOD and TSS estimates agree less well with measured values at the 

Spring Branch Station. Obviously, land use variation alone cannot precisely account for 

variations in water quality from one location to the next; nevertheless, landuse-based 

EMCs can provide good wash-off quality estimates- both the strengths and the 

shortcomings of landuse-based EMCs are apparent in the Stevenson Creek Watershed 

water quality monitoring data. 

EMC combinations that “made the numbers work” were found for lead, zinc, 

BOD, and TSS; however, these EMC combinations produced EMC values that were not 

reasonable for the land uses. The “true EMC” may not have been measured because of 

the limited number of samples that were collected. Another possible explanation for the 

difference is sediment re-suspension in Byrum Sump. The Spring Branch Station is 

located just downstream of Byrum Sump and it is likely that re-suspended sediments 

made up significant portions of the samples at this location. This would explain the 

elevated TSS levels as well as lead and zinc levels. There is normally a correlation 

between TSS and metals concentrations in stormwater runoff; furthermore, since lead and 

zinc tend to accumulate in sediments, higher levels could be expected in storm flow as 

well as base flow. 

The landuse-based EMCs are presented in Table 2.3-16 along with the percent 

variation from measured values at each station. Table 2.3-17 provides a listing of some of 

the literature values used for reference in this study. 
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Table 2.3-16 

Landuse-Based EMCs for Stevenson Creek Watershed1

 

1All concentrations in mg/l 

2Percent difference between measured loads and calculated loads using landuse-based EMCs. 

LAND USE Pb Zn BOD5 TSS TP TN 

Agricultural 0.004 0.029 15.36 27.64 0.96 1.27 

Commercial 0.006 0.044 14.68 38.36 0.40 1.37 

High Density Residential 0.013 0.147 20.49 51.41 1.14 2.35 

Highway/Utility 0.029 0.138 20.49 40.80 0.32 1.35 

Institutional 0.006 0.044 6.83 35.91 0.43 0.97 

Industrial 0.004 0.081 12.29 51.14 0.43 1.16 

Low Density Residential 0.001 0.009 11.52 7.75 0.25 1.14 

Medium Density Residential 0.001 0.011 14.72 11.02 0.28 1.48 

Open Land 0.001 0.010 10.67 5.98 0.10 0.81 

Recreational 0.001 0.007 1.71 5.98 0.10 0.81 

Natural Areas 0.001 0.002 7.68 2.72 0.18 1.03 

Water 0.001 0.002 2.73 0.82 0.10 0.81 

Agreement with Monitoring Data2

Monitoring Station Pb Zn BOD5 TSS TP TN 

Stevenson Creek 0% 0% 0% 0% 0% 0% 

Spring Branch 32% 43% 21% 24% 11% 1% 

 
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 Table 2.3-17 

Landuse-Based EMCs – Selected Literature Values1

 

1 All concentrations in mg/l 

NURP Median 

LAND USE Pb Zn BOD5 TSS TP TN 

Residential 0.1440 0.1350 10 101 0.383 2.636 

Mixed Urban 0.1140 0.1540 7.8 67 0.263 1.846 

Commercial 0.1040 0.2260 9.3 70 0.201 1.751 

Stormwater Loading Rate Parameters for Central and South Florida 

LAND-USE Pb Zn BOD5 TSS TP TN 

General Agricultural - - 3.80 55.30 0.344 2.32 

Commercial-High 

Intensity 

0.2140 0.1700 17.20 94.00 0.430 2.83 

Multi-Family 0.0870 0.0550 11.00 71.70 0.490 2.42 

Highway 0.1890 0.1340 5.60 50.30 0.340 2.08 

Industrial 0.2020 0.1220 9.60 93.90 0.310 1.79 

Low Density Residential 0.0370 0.0320 4.40 19.10 0.177 1.77 

Single Family 0.0480 0.0570 7.40 27.00 0.300 2.29 

Open Land/Recreational 0.0250 0.0060 1.45 11.10 0.053 1.25 

Water 0.0250 0.0280 1.60 3.10 0.110 1.25 

Wetland 0.0250 0.0060 4.63 10.20 0.190 1.6 

Hillsborough County 

LAND-USE PB ZN BOD5 TSS TP TN 

Agricultural 0.003 0.017 18.30 12.70 2.349 2.97 

Commercial 0.004 0.026 2.67 22.92 0.279 2.032 

High Density Residential 0.006 0.058 2.60 29.00 1.337 2.047 

Highway/Utility 0.960 0.410 24.00 261.00 0.120 4.13 

Institutional 0.004 0.026 2.67 22.92 0.279 2.032 

Light Industrial 0.006 0.096 2.87 18.20 0.332 2.275 

Low/Medium Density 

Residential 

0.008 0.022 1.00 19.00 0.401 1.363 

Open Land 0.001 0.006 3.80 11.10 0.050 2.598 

Recreational 0.006 0.004 3.80 11.10 0.050 2.598 

Upland Forest 0.000 0.000 0.00 0.00 0.000 0 

Water 0.000 0.000 0.00 0.00 0.000 0 

Wetland Forest 0.000 0.000 0.00 0.00 0.000 0 

Wetland Non-Forested 0.000 0.000 0.00 0.00 0.000 0 
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2.3.4.3 Results 

Mass loads are divided into three parts: Gross load, removed load, and net load. 

These three types of loads are described as follows: 

• Gross Load - The mass washed off, or mass generated. 

• Removed Load - The mass removed by BMPS. 

• Net Load - Gross load minus removed load. 

Load totals are provided on Table 2.3-18 and presented visually in terms of 

loading rate (lb./ac) on Figures 2.3-13 through 2.3-16. Additional details concerning the 

results of the nonpoint source loading analysis are provided in Appendix K. 

These loading estimates are intended to represent an average year. The annual 

rainfall used for these calculations was 55.6 inches – this is based on the average annual 

rainfall depth reported by the SCS in the Pinellas County Soil Survey. According to the 

“constant concentration” method which was used (refer to Table 2.3.4.2), load estimates 

for other years (or time periods) could be made by multiplying the loads presented here 

by the ratio of rainfall, for the period of interest, to 55.6. 

The highest load totals were calculated for the Upper Spring basin. Upper Spring 

basin is also the largest in terms of area; therefore, this result can be misleading. A better 

indicator of “hot spots” is loading rate, or pound per acre (refer to Figures 2.3-13 to 2.3-

16). Reviewing the results from a loading rate perspective shows the Middle Stevenson 

basin to have the worst stormwater runoff quality. For example, the net load of TSS 

originating from Upper Spring Branch is 108,743 pounds per year, and the net TSS 

loading rate is 65 pounds per acre per year. For Middle Stevenson Creek the net annual 

load of TSS is estimated at 59,604 pounds and the net TSS loading rate is 111 pounds per 

acre per year – a smaller load than Upper Spring Branch but a higher loading rate. The 

Middle Stevenson basin has an abundance of the three factors that cause high loads – 

soils with low infiltration rates, intense developed land use, and lack of treatment. 
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Table 2.3-18 

Major Basin Loads

Watershed Pb Zn BOD5 COD TSS TP TN 

Gross Load (pounds per year) 

Hammond Branch 10 80 36,441 46,777 903 3,861 10 

Jeffords Street 5 38 26,273 29,436 574 2,790 5 

Lake Belleview 15 118 37,515 73,482 1,080 3,903 15 

Lower Spring 4 36 17,527 22,031 451 1,831 4 

Lower Stevenson 11 75 33,941 49,546 817 3,715 11 

Middle Stevenson 13 104 31,534 61,338 903 3,172 13 

Upper Spring 36 325 84,074 147,929 2,907 9,021 36 

Upper Stevenson 6 49 26,642 33,141 633 2,704 6 

Total 100 826 293,948 463,680 8,269 30,997 100 

Load Removed (pounds per year) 

Hammond Branch 1 9 3,049 6,362 104 236 1 

Jeffords Street 1 5 2,889 4,090 74 208 1 

Lake Belleview 5 27 8,861 24,454 274 554 5 

Lower Spring 1 8 2,250 4,379 78 188 1 

Lower Stevenson - - - - - - - 

Middle Stevenson 0 2 678 1,734 19 68 0 

Upper Spring 10 71 15,068 39,186 607 1,048 10 

Upper Stevenson 1 6 1,781 4,936 48 101 1 

Total 20 128 34,576 85,142 1,205 2,403 20 

Net Load (pounds per year) 

Hammond Branch 9 71 33,393 40,415 799 3,625 9 

Jeffords Street 4 34 23,384 25,345 500 2,582 4 

Lake Belleview 10 90 28,654 49,028 807 3,349 10 

Lower Spring 3 29 15,277 17,651 373 1,644 3 

Lower Stevenson 11 75 33,941 49,546 817 3,715 11 

Middle Stevenson 13 102 30,856 59,604 884 3,104 13 

Upper Spring 25 254 69,006 108,743 2,300 7,974 25 

Upper Stevenson 4 43 24,861 28,205 585 2,603 4 

Total 80 697 259,372 378,538 7,064 28,594 80 
Stevenson Creek Watershed Management Plan 

Final Report 

1 

3.2 HUMAN-SOURCED FECAL CONTAMINATION STUDY 

The sampling and subsequent analysis of fecal coliforms (refer to Section 2.3.3.6) 

that was conducted last year (July 2000 – December 2000) confirmed that fecal coliforms 

from human sources are present in the watershed. While human input does not appear to 

be the dominant source of fecal coliform in the watershed, the levels of human-sourced 

fecal contamination measured during this study (refer to Appenxix J) are cause for 

concern. Human feces are considered particularly dangerous because of the humanspecific viruses transmitted exclusively by human sources. This significant finding 

underscores the need for accurate information concerning the sources of fecal 

contamination within the watershed. 

Further study is needed to better define the origins, magnitude, and spatial extent 

of fecal contamination from human sources in the Stevenson Creek Watershed. This 

study will provide information needed to plan and prioritize improvements directed at 

reducing fecal contamination within the watershed. 

3.2.1 Purpose of Further Study 

While circumstantial evidence implicates improperly functioning onsite 

wastewater treatment and disposal systems (OSTDS) in contamination of the Stevenson 

Creek Watershed, direct evidence is not available. The possible contribution of illicit 

sewage connections, sewage overflows, and the sub-drain system underlying the streets 

may also be contributing to the bacterial loading, and while there is a high likelihood that 

the source is OSTDS, information is not available concerning which OSTDS areas are 

contributing to the problem. 
Stevenson Creek Watershed Management Plan 

Final Report 

2 

3.2.2 Plan of Study 

Some of these issues can be addressed through further study, and a four-step 

approach is recommended. First, better information regarding the locations and other 

basic attributes of existing OSTDS and the sanitary sewer system is needed (Step 1). 

Secondly, additional sampling and field investigations are needed to direct attention to 

areas that are problematic with respect to fecal contamination (Step 2). Next, focused 

microbiological sampling can provide direct proof that OSTDS are contributing to water 

quality impairments (Step 3). Finally, the results of Steps 1 – 3 can be used to reach 

conclusions concerning the origins, magnitude, and extent of human-sourced fecal 

contamination within the Stevenson Creek Watershed as well as to provide information 

needed to plan improvements. 

These four steps (Existing Data Compilation and Review, Data Collection and 

Conventional Sampling, Focused Microbiological Sampling, and Data Evaluation) are 

more specifically described below. 

Existing Data Compilation and Review (Step 1) 

Existing information concerning the OSTDS and sanitary sewer system should be 

compiled. In regards to OSTDS, this information should include locations, approximate 

age, general topography, soil type, and material type, as appropriate. In regards to the 

sanitary sewer system, this information should include interviews with city staff, results 

from smoke tests, video logs, rainfall, and flow monitoring as well as population and 

overall plant flow and capacity data. These sewer system data can be used to provide 

evaluations concerning the overall soundness of the sanitary sewer system as well as the 

feasibility of connecting OSTDS areas to the central sewer system. 

One of the main purposes of the sanitary sewer evaluation is to assess the 

likelihood of sewage releases to the environment through overflows, cross-connections, 

or pipe structural problems. Loose pipe joints and cracks would not be expected to cause 
Stevenson Creek Watershed Management Plan 

Final Report 

3 

measurable exfiltration due to high groundwater; however, the possibility of capacity 

problems due to wet weather inflows should be investigated, as should the possibility of 

significant cracks or cross-connections with the storm sewer system. 

The locations of septic tanks is generally not available (refer to Section 2.3.1.2) 

but can likely be inferred by cross-referencing sewer service bills and property tax data or 

other city and county databases. Approximate age can be estimated based on the age of 

the dwelling or structure, and recent repair permits. The septic tank points can be 

intersected with available soil data to assign soil type and seasonal high water elevation. 

These OSTDS and sewer system characteristics will be used to plan the sampling 

program and to seek relationships between these characteristics and fecal contamination. 

The Healthy Beaches Tampa Bay study, an extensive, multi-agency study of Pinellas and 

Hillsborough County waters, can also be used to identify other areas of interest for the 

study if desired. 

Data Collection and Conventional Sampling (Step 2). 

The data from Step 1 can be used to develop a field investigation and sampling 

program designed to “zero-in” on problem areas. Field investigations can be used to 

collect evidence of illicit sewage connections to the storm sewer system and other 

problems (i.e. soggy drainfields, etc.). Water quality samples would be collected in 

channels and storm sewer pipes. The recommended sampling program would consist of a 

large number of samples from a minimum of two events. The large number of samples is 

for purposes of better and more refined delineation of problem areas. The sampling 

frequency will be selected based on costs with a minimum of one sample representative 

of dry conditions and one sample representative of wet conditions. Stormwater runoff 

samples are desirable, but introduce cost and logistic problems that should be carefully 

considered before they are included in this study. All samples will be analyzed for fecal 

coliforms; in addition, limited bacterial source tracking using antibiotic resistance 

analysis may be employed. 
Stevenson Creek Watershed Management Plan 

Final Report 

4 

The sampling program will draw attention to problem areas, and together with the 

information collected in Step 1, will be used to design a microbiological sampling 

program that is focused on identifying areas where OSTDS usage is problematic.

Focused Microbiological Sampling (Step 3) 

 A detailed microbiological study should be undertaken that explores the 

prevalence of human pathogens (enteric viruses) and E. coli from human sources at 

various Stevenson Creek sites. Antibiotic resistance analysis for the source of fecal 

bacteria will indicate whether the contamination is dominated by human or animal 

sources. “Tracer” studies, in which a specific bacteriophage (bacterial virus) that cannot 

infect humans is flushed down the toilets of volunteer homes, can provide evidence of the 

rate of viral transport from OSTDS to surface water. Bacteriophage studies are superior to 

dye tracer studies because the bacteriophage particles are similar in size and soil 

adsorption properties to human viruses, therefore their transport rate is a better 

approximation for that of viral pathogens than dye particles, which often predict an overly 

rapid transport rate. Piezometer wells can be used to trace the direction and magnitude of 

a contamination plume. 

If sufficient funds are available, a countywide study could be conducted in which 

the experiments mentioned above are conducted in OSTDS drainfields situated in various 

types of soil with different separation distances from the water table, and of various ages. 

Because they are time-consuming and require a great deal of expertise, such studies are 

rarely conducted and would contribute a great deal to our understanding of the processes 

governing transport of human pathogens from OSTDS drainfields. 

Data Evaluation (Step 4) 

The data collected in Steps 1 – 3 will be used to develop and prioritize 

improvement plans. In addition, correlations and other relationships will be sought so that 

the results of this study may provide useful information to other areas of Pinellas County 

that experience fecal contamination problems. 
Stevenson Creek Watershed Management Plan 

Final Report 

5 

3.2.3 Dissemination of Results to End Users 

A multi-county task force should be formed with representatives from entities 

such as city public works, the Pinellas County Department of Health, the University of 

South Florida, the Southwest Florida Water Management District, Tampa Bay Water, and 

the Florida Department of Environmental Protection. The purpose of the task force would 

be to foster communication and facilitate problem solving on water quality issues and 

studies. The synergistic potential of such a group could serve as a model for similar 

groups across the state and the nation. 
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Final Report 

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3.3 RECOMMENDED WATERSHED MAINTENANCE PLAN 

 Comprehensive, regular maintenance of stormwater management systems is 

essential to ensure the systems, once constructed, continue to function within their 

original design parameters for many years. Maintenance is also often required for 

aesthetics and safety reasons. This section outlines recommended maintenance practices 

and schedules for the Stevenson Creek Watershed. 

Open Channels. Excessive vegetation and sediment accumulation can create new 

flooding problems, and worsen those problems which already exist. In some instances, 

excessive exotic invasive vegetation and sedimentation can inhibit the growth of 

beneficial flora and fauna. Excessive vegetation in open channels, particularly exotic or 

invasive species and plants with stiff, woody stems, can greatly increase the resistance to 

flow, thereby reducing the capacity of the channel to convey floodwaters and ultimately 

resulting in higher flood levels. Excessive sediment accumulation reduces the cross 

sectional area and hydraulic radius of the channel, creating a similar effect. In addition, 

sedimentation within concrete-lined channels can allow the growth of nuisance 

vegetation where none was assumed to exist in the roughness coefficients used original 

design calculations; as has occurred within the channel segment between Court Street and 

Pierce Street. 

 Proposed Watershed Management Plan Projects 1A, 1E, 1F, 2A, 4B, and 4C are 

improvements to the main channels that incorporate features that will allow improved 

access for maintenance, including approximately 4,000 linear feet of new maintenance 

access roads adjacent to Stevenson Creek and Spring Branch. These maintenance access 

ways typically consist of earthen roads that will facilitate equipment access for slope 

mowers, small dump trucks, and excavators. The width of the proposed access ways 

varies from 12’ to 25’ depending on the nature of the anticipated maintenance activities, 

whether access will be from one side or both sides of the drainage course, and the 

availability of land. 
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 The recommended maintenance practice for open channels is mowing, and if 

necessary, hand removal of invasive vegetation. Spraying of herbicide should be used 

only in rare cases where lack of access and/or manpower prohibits the alternative 

methods. Any herbicide spraying should be conducted in compliance with the City of 

Clearwater National Pollutant Discharge Elimination System (NPDES) permit, which 

requires the implementation of a spray reduction program. The recommended 

maintenance type and frequency for each major open channel segment within the 

Stevenson Creek Watershed is presented Table 3.3-1. 

Table 3.3-1 Recommended Channel Maintenance Plan 

Channel Segment Applicable 

Improvement 

Project 

Recommended 

Maintenance 

Type(s) 

Recommended 

Frequency 

Stevenson Creek 

Stevenson Creek - US 

Alt. 19 to Douglas 

Avenue 

Stevenson Creek 

Estuary Restoration 

Plan (U.S.A.C.O.E.) 

Periodic removal of 

exotic and invasive 

plant species 

Once every 2-5 

years, or as 

needed 

Douglas Avenue to 

Betty Lane 

N/A Periodic removal of 

exotic and invasive 

plant species 

Once every 2-5 

years, or as 

needed 

Betty Lane to 

Proposed Sediment 

Sump Control Weir 

Stevenson Creek 

Phase 1 (W.K. 

Daugherty Plans) 

Initial dredging of 

accumulated 

sediment, periodic 

removal of exotic 

and invasive plant 

species 

Once every 2-5 

years, or as 

needed 

Palmetto Street 

Sediment Sump 

WMP Project 2A Dredging Annually 

Palmetto Street to 

Drew Street 

N/A Periodic removal of 

exotic and invasive 

plant species 

Once Every 2 

years, or as 

needed 

Drew Street to Pierce 

Street 

Stevenson Creek 

Phase 1 (W.K. 

Daugherty Plans) 

Periodic removal of 

accumulated 

sediment 

Once every 5 

years, or as 

needed 

Pierce Street to Court 

Street 

Stevenson Creek 

Phase 2 (CDM 

Plans) 

Mowing Semi-annually 
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Table 3.3-1 (Continued) Recommended Channel Maintenance Plan 

Channel Segment Applicable 

Improvement 

Project 

Recommended 

Maintenance 

Type(s) 

Recommended 

Frequency 

Mowing of 

embankment slopes 

and grassed areas 

Monthly during 

the growing 

season 

Court Street to Druid 

Road 

WMP Project 3A 

(Glen Oaks) 

Initial monitoring 

and maintenance of 

created wetland 

areas 

Quarterly for 

the first year, 

Semi-annually 

thereafter, until 

beneficial 

vegetation is 

well established 

Repair vandalism 

damage to gabion 

walls 

Druid Road to Jeffords As needed 

Street 

Stevenson Creek 

Phase 2 (CDM 

Plans) 

Dredge sediment 

from Jeffords Street 

sediment sump 

Semi-annually, 

or as needed 

Jeffords Street to 

Lakeview Road 

WMP Project 4A Mowing Semi-annually 

Lakeview Road to Mowing Semi-annually 

Bellevue Boulevard 

WMP Project 4B 

Removal of 

sediment from 

behind rock weirs 

Annually, or as 

needed 

Mowing of 

embankment slopes 

and grassed areas 

Monthly during 

the growing 

season until tree 

canopy is 

established, 

semi-annually 

thereafter 

Bellevue Boulevard to 

St. Thomas Drive 

WMP Project 4C 

Removal of 

sediment from 

upstream of 

proposed Bellevue 

Blvd control weir 

Annually, or as 

needed 

St. Thomas Drive to 

Belleair Boulevard 

N/A None N/A 

Belleair Boulevard to 

South Ridge 

N/A Mowing Semi-annually 
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Table 3.3-1 (Continued) Recommended Channel Maintenance Plan 

Channel Segment Applicable 

Improvement 

Project 

Recommended 

Maintenance 

Type(s) 

Recommended 

Frequency 

Spring Branch 

Stevenson Creek to 

Douglas Avenue 

N/A Periodic removal of 

exotic and invasive 

plant species 

Once every 2-5 

years, or as 

needed 

Douglas Avenue to 

Sunset Point Church 

N/A Jurisdiction of 

Pinellas County 

N/A 

Sunset Point Church to 

King’s Highway 

WMP Project 1A.1 Mowing Semi-annually 

Byram Pond WMP Project 1E Dredging Annually 

Byram Pond to Union 

Street 

WMP Project 1F Mowing Semi-annually 

Hammond Branch 

Stevenson Creek to 

King’s Highway 

N/A Periodic removal of 

exotic and invasive 

plant species 

Once every 2-5 

years, or as 

needed 

Flagler Drive Ditch, 

Highland Avenue to 

Keene Road 

N/A Mowing Semi-annually 

CSX Railroad north 

swale, Highland Ave. 

to Sharondale Drive 

WMP Project 5A Mowing Semi-annually 

Jeffords Street Branch 

600’ west of Lake Ave 

to Lake Avenue. 

WMP Project 7C Mowing Semi-annually 

Mowing of 

embankment slopes 

and grassed areas 

Proposed Pond at Semi-annually 

Barry Road and 

Tuscola 

WMP Project 7C 

Initial monitoring 

and maintenance of 

created wetland 

areas 

Quarterly for 

the first year, 

Semi-annually 

thereafter, until 

beneficial 

vegetation is 

well established 

 In addition to the main channel segments listed in the above table, maintenance of 

the CSX railroad ditch that runs parallel to Maple Street, from Betty Lane to North 
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Greenwood Avenue is recommended. The City currently owns a narrow tract of land 

adjacent to the south side of the ditch that could be used for maintenance access. Regular 

maintenance of this ditch would alleviate a structure FPLOS deficiency at 512 

Washington Avenue. 

 Created Wetlands and Littoral Shelves. Proposed Projects 1C, 2D, 3A, 6A, 7A, 

7B, and 7C are improvements that incorporate created wetland and/or littoral shelf areas. 

Monitoring and maintenance of created wetland areas is recommended to ensure the 

success of the wetland plantings. Maintenance should be conducted quarterly for the first 

year, and semi-annually thereafter, until beneficial vegetation is well established. 

 

Inlets and Control Structures. Curb and ditch-bottom inlets should be inspected at 

least annually for blockages due to vegetation, sediment, trash, etc, and for structural 

integrity and safety. Cleaning of existing and proposed catch basins, or water quality 

inlets, and CDS units should be conducted based on an established schedule. The City of 

Clearwater currently has two (2) vacuum trucks for this purpose, and is in the process of 

purchasing a third one. Periodic inspection of all existing and new water level control 

structures for structural integrity, safety, accumulated sediment, vegetation, and 

blockages should be conducted by qualified engineering staff. Vegetation and 

accumulated sediment should be removed as needed from around water level control 

structures to ensure their proper functioning. 

 

Culverts and Storm Sewers. The Stevenson Creek Watershed contains many 

existing culverts and storm sewers that are several decades old. Most of these culverts 

are still in serviceable condition and do not require regular maintenance. Those that were 

identified to be in an obvious state of deterioration are recommended for replacement in 

one of the 28 recommended projects described in Section 3.1. However, all infrastructure 

is continually deteriorating, and culverts, storm sewers, and inlets should be inspected 

periodically (approximately every 3 to 5 years) to identify those in need of replacement. 

When culverts and storm sewers are identified for replacement, the design should be 
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evaluated to determine the appropriate size for the culvert to meet current design criteria 

for flood protection level of service. 

Golf Course Best Management Practices. There are currently three golf courses 

within the Stevenson Creek Watershed. The two largest courses include the Clearwater 

Country Club Course and the Clearwater Executive Course. The third course is the Glen 

Oaks Golf Club, a small course that under this plan is proposed to be converted into a 

stormwater detention facility. Golf courses are some of the most highly maintained 

developed areas in the state. The expanses of turf grass, manicured landscaping, and 

sparkling blue water traps lead some people to think that because these areas are not 

paved, that they are beneficial to the environment. What most people don’t realize is that 

a considerable amount of physical and chemical manipulation of the natural environment 

must be undertaken to create this illusion of perfection. The physical alterations include 

site grading and changing historic drainage patterns, removing native vegetation, and 

planting exotic, typically high-maintenance vegetation. The chemical manipulations 

include applications of: 

• Fertilizers to help the exotic vegetation survive in the foreign environment, 

• Insecticides to protect the exotic vegetation against predators for which they have 

no natural defense, 

• Herbicides to reduce competition from other exotic species, and 

• Fungicides to counteract the effects of the excessive amounts of water the exotic 

turf grasses require. 

 When these chemicals are used, the excess typically is found in surface and ground 

water, where they can be extremely detrimental to the environment. The effects of 

pesticides and fertilizers on surface and groundwater quality should motivate golf course 

operators to opt for application methodologies and the selection of substances with the 

least potential to cause water quality problems. 

 A comprehensive program of best management practices specifically for golf 

courses was developed by the University of Florida Institute of Food and Agriculture 

Sciences (IFAS). This program discusses ways to reduce or eliminate the need for 
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fertilizers and pesticides, and recommends more environmentally friendly substances to 

use when needed. Some of the recommendations include: 

• Use native plants in the landscape. Native plants have adapted to the 

environment and require less water to survive. They also have natural defenses 

against many predators, which will reduce the need for pesticides. Native plants 

will also provide habitat for wildlife. 

• There are turf grasses that have been developed for use on golf courses that are 

hardier and require less water and fertilizer. The Pinellas County Agricultural 

Extension Office has information on these newly developed grasses. 

• Before using a pesticide, identify the target pest. This is essential for the 

selection of the proper pesticide to be used. Once the pest is identified, check 

with the IFAS to determine the recommended pesticides for that species. These 

recommendations will consider soil properties such as runoff potential, leaching 

potential, and the relative toxicity of the pesticide. 

• The application methodology is an important factor to consider when using 

pesticides and fertilizers. Applications directly on the soil or incorporated into 

the soil will likely make more product available for leaching or runoff loss. 

Applications to foliage may lose some product to evaporation, absorption into the 

foliage, or decomposition in sunlight and thereby would reduce the amount 

available for wash-off and transport to water bodies. 

• Create littoral shelves within the water traps and plant them with emergent 

aquatic vegetation. The vegetation will improve water quality and reduce the 

occurrence of algal blooms. Fewer chemicals will be needed to keep the water 

features clear. 

• Use organic pesticides and fertilizers when possible. Many products have been 

developed especially for use on golf courses and have been tested successfully by 

the IFAS. Information on these products is available from the county extension 

service. 
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3.4 PUBLIC AWARENESS AND INVOLVEMENT PROGRAMS 

An essential component of any restoration plan is a focused and integrated public 

education and involvement program. Many agencies, both public and private, have 

information for the homeowner regarding practices that can be implemented at the 

individual home level for the benefit of the local environment. Most residents, when 

educated regarding their immediate environment and their potential impact upon it, 

become more interested in acting more responsibly. 

3.4.1 Adopt-a-Creek Program for Stevenson Creek 

One of the most successful methods of encouraging public involvement/awareness in 

the Tampa Bay area is to establish a citizen’s group that “adopts” a piece of property or 

natural feature. Adopt-a-Pond, Adopt-a-Highway, and Adopt-a-Shoreline are examples 

of such programs in which a group of citizens accepts the responsibility of maintaining a 

section of the property on a regular basis. The Adopt-a-Pond program in Hillsborough 

County has been very successful in the past years, and a similar program for Stevenson 

Creek could be implemented. The program would encourage residents along the creek to 

take interest in keeping the creek clean and to help prevent water quality problems. 

No regularly scheduled program of adoption and maintenance is currently offered for 

Stevenson Creek, despite the obvious interest and concern of the local residents. It is 

recommended that a program of this nature be implemented within the watershed, to 

accomplish the maintenance and enhancement as needed. The greatest benefit to the 

watershed would be the regular removal of trash and exotic vegetation within and 

adjacent to the creek. The creek can be segmented and the responsibilities distributed 

among the various civic groups and homeowner associations. A group leader will be 

trained in plant identification and the proper methods of eradication. Pam Leasure with 

the Pinellas County Department of Environmental Resources (telephone: 727-464-4793) 

can be contacted if there is an interest in implementing an Adopt-a-Creek program for the 

Stevenson Creek Watershed. 
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3.4.2 Proper Use of Pesticides and Fertilizers 

3.4.2.1 Pesticide Use 

Pesticides are applied to control a pest species, usually by reducing the population to 

an acceptable level. This objective can sometimes be achieved without damage to nontarget species. However, when pesticides are broadcast sprayed over lawns and fields, a 

variety of onsite non-target organisms is impacted. In addition, much of the sprayed 

pesticide invariably drifts away from the intended site and deposits in non-target 

organisms and ecosystems. Many pesticides are not thoroughly tested prior to 

distribution and long term effects are not determined until too late. The pesticide DDT is 

a well-known example. Although the use of DDT was banned in the United States over 

twenty-five years ago, there are several sites within Tampa Bay where sediment 

concentrations exceed the No Observable Effects Level (NOEL) (TBNEP 1996). 

A preferable alternative to pesticide use is integrated pest management (IPM). 

Within the context of IPM, acceptable pest control is achieved by employing an array of 

complementary approaches. The can include: 

• use of natural predators, parasites, and other biological controls 

• Use of pest resistant varieties of turf grass and landscape plants. Native plant 

species are frequently more resistant to pests and pathogens than non-native 

species. 

• Modification of environmental conditions so as to reduce the optimality of the 

pest habitat. This would entail not planting monocultures of specific plants. 

• Careful monitoring of pest abundance, and using pest-specific, less toxic 

pesticides such as Bacillus thuringensis. 

• Use of pesticides only when they are required as a specific component of the IPM. 

Information regarding insect pests, the proper use of pesticides and IPM is available 

at the Pinellas County Cooperative Extension Service or visit the web site at 

http://gnv.ifas.ufl.edu/~FAIRSWEB/IPM/IPMFL/IPMFL.HTM. 
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3.4.2.2 Fertilizers 

Most homeowners use too much fertilizer in their landscapes. Over-fertilizing 

actually encourages the growth and proliferation of certain insects and diseases and 

increases maintenance needs. When choosing fertilizers, homeowners should request 

products that contain nutrients in water-insoluble or controlled-release form. These 

fertilizers dissolve slowly into the soil, reducing amount of nutrients lost in stormwater 

runoff. The PCCES has free information regarding the most environmentally friendly 

fertilizers to purchase, and how they should be applied. This information can be obtained 

at the extension office or at the web site listed above. 

3.4.3 “Green” Thumb Landscaping Practices 

The University of Florida Cooperative Extension Service, in partnership with the 

Tampa Bay National Estuary Program, the Florida Sea Grant College Program and 

numerous other environmental agencies, has prepared a Landscaping Guide for the 

Florida Yards and Neighborhoods Program. This informative guide describes the 

benefits of using native plants in the landscape and how to recreate the habitat that was 

lost when development occurred. The guide explains such practices as composting, 

mulching, fertilizing, and watering, and how these common practices can be undertaken 

without comprising the environment. The program also touches on such issues as 

maintaining waterfront property in a non-invasive manner, how to maintain a septic 

system, and how to attract wildlife to your backyard. This information is free from the 

PCCES or visit the web site at http://coop.co.pinellas.fl.us/. 

A valuable source of information for creating an environmental landscape is the 

National Wildlife Federation (NWF). This organization has prepared a program that 

educates homeowners in the benefits of landscaping to attract wildlife and provides the 

basic information needed to develop wildlife habitat in a residential setting. This 

program is called the Backyard Habitat program, and participating residents can have 

their houses certified as habitat by the NWF. This and other useful topics are discussed 

on their web site at http://www.nwf.org/. 
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Another successful program is the Naturescape Urban Wildlife Enhancement 

Program, developed by the Pinellas County Department of Environmental Management 

(PCDEM). The booklet was produced for the residents within the Allen’s Creek 

watershed, but the principles are applicable to all watersheds in central Florida. The 

booklet provides ideas on how to reduce water loss when irrigating the landscape, how to 

use less pesticides and fertilizers, how to create wildlife habitat, and what plants to put in 

the landscape, as well as what plants to avoid. This booklet is free and can be obtained 

from the PCDEM. 

The Southwest Florida Water Management District has produced a significant 

amount of information on Xeriscaping. This method of landscaping reduces the amount 

of water that is needed by planting native and non-native plants that require little water, 

reducing the square-footage of water-dependent turf-grass, and by planting species that do 

require water in zones that can be irrigated more efficiently. Other aspects of Xeriscaping 

include the use of mulch to reduce moisture loss from the soil, and the use of mulch made 

from exotic species such as melaleuca and eucalyptus or from recycled wood products. 

Information can be obtained from SWFWMD free or for a nominal fee. The SWFWMD 

Tampa Field Office can be contacted at (813)-985-7481 or on the world wide web at 

http://www.swfwmd.state.fl.us/watercon/xeris/swfxeris.html. Information about native 

plants can be obtained at the Florida Native Plant Society web site at 

http://www.fnps.org/index.html. Additional information regarding xeriscaping can be 

obtained from the PCCES on their web site at 

http://coop.co.pinellas.fl.us/Toughcom.htm. 

3.4.4 Florida Yards and Neighborhoods Program 

The Pinellas County branch of the Florida Yards and Neighborhoods Program was 

developed by the National Estuary Program and is managed by the Pinellas County 

Cooperative Extension Service. This program utilizes the educational elements by 

helping neighborhoods work together to treat area-specific problems such as nutrient- and 
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chemical-rich stormwater runoff, yard waste disposal, misuse of chemical biocides, and 

improper shoreline maintenance. 

The first step in participation with this program is a preliminary meeting with FYNP 

staff and homeowners associations requesting participation in the program. Each of the 

homeowners is given a detailed questionnaire to determine their specific yard 

maintenance activities. If a neighborhood meets the requirements for investigation by the 

FYNP, a team of environmental specialists performs inspections, targeting problems 

associated with landscape practices and stormwater runoff. Results of these inspections 

are analyzed and presented to the homeowners association along with suggestions on 

ways to remedy current environmental problems through sustainable yard maintenance 

practices. 

3.4.5 Storm Drain Marking Program 

An important component of public education for watershed management is the storm 

drain-marking program. This program enlightens citizens about the potential adverse 

effects of stormwater runoff entering surface water bodies. Many people allow paint, 

petroleum products and yard wastes to wash into gutters and into storm drains without 

consideration of the potential effects on surface waters. The storm drain marking 

program involves simply painting legible messages on the drains to remind the public 

where the drains lead. Within the Stevenson Creek Watershed, the messages may read 

“NO DUMPING - DRAINS TO CLEARWATER HARBOR," or “DUMPING HERE 

POLLUTES STEVENSON CREEK AND CLEARWATER HARBOR”. Some of the 

messages may include illustrations of fish, manatees, wading birds, or dolphins. 

The storm drain marking program has been successfully implemented within other 

areas of the City of Clearwater, and could be implemented within the Stevenson Creek 

Watershed without significant expense. Volunteers from local schools and civic groups 

could be organized to conduct the marking under the supervision of officials from various 

Tampa Bay agencies such as Tampa Baywatch, Tampa Bay National Estuarine Program, 

and city and county government. Items needed for the drain marking include traffic 
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cones, a broom, paint, safety vests, instruction sheets, and stencils. These items can be 

purchased or fabricated from materials costing less than $220.00. 
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3.5 EXOTIC PLANT ERADICATION PROGRAM 

Native plant communities evolve with a complex relationship of natural controls that 

keep them in balance. These natural controls may include environmental requirements, 

competing plant species, herbivores including insects, and pathogens. When exotic 

plants are introduced to areas, they often have a competitive advantage over native plants 

because natural controls of the exotic plants are not present. Removal of exotic plant 

species and restoration of native communities includes supplemental control methods to 

replace natural controls. These supplemental controls may include manual and/or 

mechanical removal, physical control such as fire or water level manipulation, chemical 

control including application of herbicides, and biological controls such as natural insect 

or pathogenic controls. The ultimate exotic plant control objective is to remove exotic 

species and re-establish natural conditions that will restore normal competitive processes, 

reducing the potential for re-invasion and the requirement for continual maintenance. 

Exotic plant species commonly found in the Stevenson Creek Watershed are listed in 

Table 3.5-1: 

Table 3.5-1 Exotic Plant Species Found in the Stevenson Creek Watershed

Scientific Name Common Name Scientific Name Common Name 

Casuarina equisetifolia Australian pine Melaleuca 

quinquenervia 

Melaleuca 

Colocasia esculenta Wild taro Melia azedarach Chinaberry 

Dioscorea bulbifera Air-potato Panicum repens Torpedo grass

Eichhornia crassipes Water-hyacinth Ricinus communis Castor bean 

Enterolobium 

contortisiliquum 

Ear-pod tree Sapium sebiferum Chinese tallow tree 

Hibiscus tiliaceus Mahoe Schinus terebinthifolius Brazilian pepper 

Hydrilla verticillata Hydrilla Typha sp. Cattail 

Leucaena leucocephala Lead tree Urena lobata Caesar's weed 

Ludwigia peruviana Primrose willow Wedelia trilobata Wedelia 

Citation: Florida Exotic Pest Plant Council. FLEPPC 1999 List of Florida's Most Invasive Species. 

Internet: http://www.fleppc.org/99list.htm
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Current exotic plant control techniques used by City of Clearwater employees for 

non-aquatic vegetation include manual removal, herbicide application, and burning. 

Mechanical removal is not effective for control of Australian pine, Brazilian pepper, or 

melaleuca when used alone because the disturbance of soil creates conditions for 

regrowth from seeds and root fragments, and allows further invasion by pioneering exotic 

plants. Intense follow up with other control methods, preferably herbicide, is also 

required. Burning and water level manipulation are not applicable within this watershed 

due to the high density of the residential and commercial areas. 

Aquatic nuisance vegetation is removed from lakes and ponds via herbicide 

application, manual removal, and the installation of native species. Private contractors do 

the majority of the exotic plant maintenance. The maintenance activity in the watershed 

is concentrated on the removal and treatment of emergent nuisance species such as 

Ludwigia peruviana, Typha sp., and Eichhornia crassipes. These plants can choke 

waterways and cause flooding. 

3.5.1 Brazilian Pepper 

Brazilian pepper is the most aggressive exotic in the watershed, and has been found 

in every terrestrial plant community. This exotic forms dense monocultures in previously 

disturbed areas and along roadside ditches. Brazilian pepper seeds are commonly 

dispersed by birds and small mammals. 

Removal techniques for Brazilian pepper currently used in the City of Clearwater 

include manual removal and herbicide application. Herbicide application involves basal 

bark application of a Garlon 4/diesel solution in a minimum 4-inch band approximately 6 

to 12 inches above ground. The Garlon 4/diesel solution consists of two ounces of 

Garlon 4, Ortho X-77 spreader, and one quart diesel mixed into three quarts of water. 

Diesel is added to the herbicide to increase adherence to the stem, and decrease the 

potential for wash-off during rainfall. Retreatment may be required for larger stems. 

Dead stems are left standing to decay, or are removed to a landfill or mulch site. Mist 

application of a Garlon 4/diesel solution using one part Garlon 4 in 50 parts water is also 

required for treatment of seedlings under mature trees. Garlon 4 should also be applied to 
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roots to eliminate regrowth. Safety equipment required during application includes a 

respirator, safety face shield, rubber gloves, and protective clothing. Eyewash should be 

carried to flush eyes in case of accidental splash or spray. 

3.5.2 Australian pine 

Australian pine also spreads through dispersion of seeds deposited along shorelines. 

Australian pine grows rapidly, forms dense monocultures, and tolerates saline conditions 

and a wide range of soil moisture. The dense shade and thick litter layer produced by 

stands of Australian pine prevent germination and growth of native species that provide 

food for birds and small mammals. Australian pine boles do not decay readily after being 

killed by girdling and tend to dry without decaying (“petrify”). 

Australian pine removal techniques currently used in the City of Clearwater include 

cutting of the stem with a chainsaw, and spraying the stump with the Garlon 4/diesel 

solution described for Brazilian pepper. The cut stem is left to dry (“petrify”) for later 

disposal or use as fuel source. The effects of herbicide application will be noticeable 

within 3 to 7 days of application. Although trees can be treated throughout the year, 

herbicide application in April and May is most effective, followed by applications in June 

or July. Retreatment is performed after one month if required for larger trees. Small 

stems can be hand-pulled, bagged, and burned. The Garlon 4/diesel solution is also 

applied to roots to eliminate regrowth. Safety equipment required during application is 

the same as described for Brazilian pepper. 

3.5.3 Melaleuca 

Development activities, water level alterations, and climatic conditions make all 

areas in south and central Florida vulnerable to invasion by this exotic. Melaleuca grows 

very rapidly with trees as young as two years producing seeds. Melaleuca bark is thick 

and fire resistant; consequently, this exotic cannot be controlled by fire. Viable seeds 

formed on trees cannot be killed with herbicide or by cutting of the stem because any 

interference with water flow through the xylem to the seed capsules triggers immediate 

seed release. 
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Melaleuca removal techniques currently utilized in the City of Clearwater include 

removal as encountered including manual cutting of the trunk, followed by stump 

treatment with herbicide Garlon 4. Seed capsules are put in plastic garbage bags within 

20 minutes of stem cutting for disposal at the Pinellas County landfill. Landfill disposal 

includes burial at a depth sufficient to allow decay of the seed capsules, eliminating the 

potential for future sprouting. Stems are cut up and left to decay. Small seedlings are 

hand pulled, bagged, and burned; saplings too large to be pulled are sprayed with Garlon 

4. Garlon 4 is also applied to the ground within an approximately 10-foot radius of the 

trunk to prevent growth of seedlings. Retreatment is provided as necessary at 

approximately six-month intervals. 

3.5.4 Other Exotics 

Other exotics currently present in areas within the watershed include ear-tree, 

chinaberry, Caesar weed, and air potato. These exotics are more easily controlled than 

those listed above. Removal techniques currently used for ear-tree include girdle and 

application of the Garlon 4/diesel solution described for Brazilian pepper. Chinaberry 

and air potato are controlled through manual removal and application of Garlon 4. These 

exotics are removed as encountered. 

3.5.5 Estuary Restoration Plan 

The U.S. Army Corps of Engineers is currently reviewing an application from the 

City of Clearwater to participate in a Brownfields demonstration project using the 

Stevenson Creek Estuary. The proposed Section 206 project will involve the removal of 

approximately 80,000 cubic yards of muck sediments from the creek between the 

Douglas Avenue Bridge and the North Fort Harrison Bridge. In addition to the muck 

removal, the project will involve the removal of nuisance species that currently grow on 

some of the sediment deltas and on the shoreline of the creek. Species to be removed 

include cattail, torpedo grass, Brazilian pepper, melaleuca, and mahoe. Once the 

nuisance vegetation accumulated sediments are removed, the shorelines of the creek will 

be planted with native vegetation, such as mangroves, cord grass and giant leather leaf 

fern. 
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3.5.6 Summary and Recommendations 

The proposed watershed improvements are expected to effect exotic control 

activities in areas currently being maintained, and to facilitate removal and maintenance 

activities in additional exotic species affected areas by increasing accessibility. Some 

exotic species removal may be proposed as mitigation for impacts to wetlands during 

watershed improvements. 

Precautions must be taken during all grading and filling activities associated with the 

watershed improvements, as well as removal of large-stem exotics, to minimize the 

enhancement of seedbed conditions. Enhancement may arise from scraping of existing 

seedbeds or deposition of materials that provide a seed source for exotics. 

Damage to non-target vegetation and potential water contamination are potential 

concerns for exotics control. Herbicides effective for Australian pine and Brazilian 

pepper control are not selective and many native species are highly sensitive to these 

herbicides. Over spray and heavy rainfall following application can wash the herbicide 

off the trunk and damage non-target vegetation and/or enter surface water. For these 

reasons, the use of injection techniques instead of basal bark or girdle applications is 

preferred for exotics control in wetlands. In addition, while the current practice of 

leaving stems to decay or “petrify” provides some habitat value as bird perches and small 

mammal cover, stems and debris generated from larger scale exotics removal activities 

must be removed from wetland areas. 

Exotic plant species control methods and recommendations discussed above are 

primarily applicable to the undeveloped public lands within the watershed. Development 

of a detailed plan for exotics removal and maintenance is recommended. 
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3.6 LEGAL AND REGULATORY FRAMEWORK 

This section summarizes the existing legal and regulatory framework governing 

stormwater and environmental management within the City of Clearwater and the 

Stevenson Creek Watershed. The first four subsections outline the regulatory authority 

of federal and state agencies over watershed management issues. Implementation of the 

Watershed Management Plan will require close coordination with these agencies. The 

fifth and final subsection concerns the City of Clearwater and its stormwater and 

environmental legal framework governing items such as funding of capital improvement 

projects, stormwater levels of service, and municipal codes and ordinances regulating 

stormwater discharges, erosion control, etc.

3.6.1 U.S. Army Corps of Engineers 

The U.S. Army Corps of Engineers (USACE) regulates dredge and fill activities 

within existing wetlands and other surface waters of the United States, including both 

natural and man-made lakes and ponds. Federal permitting of the recommended projects 

of the Stevenson Creek Watershed Management Plan will require close coordination with 

the USACE. The Environmental Resource Permit (ERP) program, implemented jointly 

in 1995 with the state water management districts, was designed to streamline the 

permitting process. Although the ERP application is described as a joint state and federal 

permit vehicle, the USACE application process can be lengthy and complicated even for 

relatively simple projects. The USACE issues four types of permits depending upon the 

type of activity proposed. The categories of permits include the 1) Letter of Permission, 

2) Individual Permit, 3) Nationwide Permit, and 4) Regional or General Permit. 

The permitting process for improvements proposed in this management plan will be 

a complex process. Because significant drainage improvements are proposed, a 

conceptual permit approach is recommended to facilitate the process. Once conceptual 

approval is achieved, the projects within the management plan can be permitted 

individually and expeditiously. More information regarding federal permitting can be 

obtained by calling Stuart Santos at (904)-232-2018 or by visiting the USACE web site at 

http://www.saj.usace.army.mil/permit/types_of_permits.htm.
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3.6.2 U.S. Environmental Protection Agency

The National Pollution Discharge Elimination System (NPDES) is a federal program 

implemented as a result of the Clean Water Act. This program, in conjunction with the 

stormwater pollution prevention plan (U.S. EPA 833-R-92-001, October 1992) requires 

permit approval and compliance with water quality standards for stormwater discharges 

from municipal and industrial stormwater treatment facilities and construction sites. In 

1998, the EPA issued the Municipal Separate Stormwater Sewer System Permit (MS4 

Permit) for Region IV, that includes several municipalities including the City of 

Clearwater. The 1997 Stormwater Management Plan for the City of Clearwater 

addressed many of the requirements for compliance with the MS4 Permit, and made 

recommendations for current and future needs. The implementation of the capital 

improvements recommended in the Stevenson Creek Watershed management plan, along 

with the maintenance of standard best management practices during and after 

construction, will help ensure compliance with the MS4 Permit. 

3.6.3 Federal Emergency Management Agency 

In 1968, the Federal Emergency Management Agency (FEMA) began the national 

flood insurance program (NFIP), a cooperative program between FEMA and local 

governments, of which the City of Clearwater is a participant. The purpose of the NFIP 

is to identify and map areas of special flood hazards (SFHA), to regulate building 

construction and related activities within SFHA’s, and to make affordable flood insurance 

available to owners of homes and businesses. 

The maps of SFHA’s are known as flood insurance rate (FIRM) maps. Once 

adopted, FIRM maps can be amended by the local community through a formal 

FEMA/NFIP application process known as a letter of map revision (LOMR). As part of 

this Watershed Management Plan, the FIRM maps for the City of Clearwater, last 

updated in 1983, will be amended based on the existing conditions hydrologic and 

hydraulic modeling of the Stevenson Creek Watershed, and the corresponding 100- and 

500-year floodplain maps and flood profiles illustrated on Figures 2.1-15 through 2.1-23. 
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The basis for the revision will be better technical information, and a more detailed 

analysis than was conducted for the original flood insurance study. 

Since 1990, the City of Clearwater has participated in the NFIP’s community rating 

system, which gives flood insurance premium reductions to policyholders in communities 

that take additional measures to reduce flood damages, beyond the minimum standards 

necessary to participate in the NFIP. Under the system, communities earn “credit points” 

for floodplain management activities within the four categories of public information, 

mapping and regulation, flood damage reduction, and flood preparedness. Communities 

are assigned a rating between 1 and 10, with class 1 requiring the most credit points and 

giving the greatest premium reductions, and class 10 providing no reduction in premiums. 

Currently, the City of Clearwater enjoys a “class 7” status in the CRS, which puts 

Clearwater in the top 16% of participating communities, and translates directly into a 

15% premium reduction for policyholders within an identified SFHA. 

Implementation of the Stevenson Creek Watershed Management Plan will qualify 

the City for additional credit points in the CRS through flood damage reduction. As 

indicated in Section 3.1, implementation of the flood protection capital improvements of 

the Plan will eliminate 73% of the identified structure flood protection level of service 

(FPLOS) deficiencies within the watershed. Under the CRS, additional credit points are 

also provided to communities that institute programs to relocate or floodproof structures 

within the 100-year floodplain. It is recommended that concurrent to implementation of 

the flood protection capital improvement (CIP) projects, the City work with FEMA, the 

NFIP/CRS, and the owners of the remaining FPLOS deficiencies to relocate or 

floodproof those remaining FPLOS deficient structures that cannot be cost-effectively 

remedied by the recommended CIP projects. FEMA provides technical assistance and in 

many cases, grant money to help fund the flood proofing or relocation of floodsusceptible structures. Additional information regarding the National Flood Insurance 

Program is available at http://www.fema.gov/nfip. 
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3.6.4 Southwest Florida Water Management District / Florida Department of 

Environmental Protection 

The Environmental Resource Permit (ERP) Program that became effective on 

October 3, 1995 governs watershed management activities in Florida including design of 

new development and stormwater management facilities with respect to allowable rates 

of runoff, stormwater treatment, and impacts to floodplains and wetlands. The program 

represents the merging of the former wetland resource permit program from Chapter 403, 

Florida Statutes (F.S.), with the management and storage of surface water (MSSW) 

permit program in Part IV of Chapter 373, F.S. The ERP Program applies statewide, 

except within the Northwest Florida Water Management District, where the former 

wetland resource permitting program remains in effect. 

To allow an applicant to deal with only one agency when seeking an ERP, the 

review and approval or denial of the ERP permit application will be performed by either 

the Department of Environmental Protection (DEP), or the Southwest Florida Water 

Management District (SWFWMD), depending upon the type of activity involved. 

Operating agreements have been signed by the agencies to specify the responsibilities 

between them. Information regarding the type of activity that would require coordination 

with the DEP is available at their web site at http://www.dep.state.fl.us/. 

Any projects within the watershed that are funded fully or partially by the SWIM 

program will also require permit review by the DEP, to avoid the potential for charges of 

a conflict of interest. The majority of the permit applications for capital improvements 

within the Stevenson Creek watershed will likely be made through SWFWMD. 

Additional information on State Environmental Resource Permitting is available at 

http://www.swfwmd.state.fl.us/osp/permits.htm.

3.6.5 City of Clearwater 

Comprehensive Plan. 

The City of Clearwater Comprehensive Plan, as adopted in May of 2000, includes 

nine major elements. Among the goals stated within these nine elements are the 

conservation, protection, and restoration of the quality of surface waters within the City, 
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the conservation and protection of wildlife habitat, and the management of the quantity 

and quality of stormwater runoff. The comprehensive plan identifies the need to 

“continue to prepare stormwater management plans which will identify and prioritize the 

implementation of programs to improve and enhance stormwater quality and quantity.” 

Other specific goals, needs, and policies related to watershed management stated within 

the comprehensive plan are highlighted below: 

Future Land Use Element

• No new development or redevelopment will be permitted which causes the level 

of City services (traffic circulation, recreation and open space, water, sewage 

treatment, garbage collection, and drainage) to fall below minimum acceptable 

levels. 

Utilities Element – Sanitary Sewer

• New septic tanks should not be permitted. Residents located in nearby 

unincorporated areas using septic tanks should connect to the City sewage 

system, as sewer lines become available. 

Utilities Element – Stormwater Management

• The City of Clearwater needs to continue to monitor the stormwater management 

utility fee rate structure and amend it as required to remain competitive and 

maintain an adequate funding source to provide revenue for flood control, 

maintenance, retrofitting, and treatment of stormwater. 

• The City of Clearwater needs to take advantage of any alternative funding 

opportunities that may become available from any State Agency with regard to 

watershed management and/or general stormwater improvements. 

• The City of Clearwater needs to continue to reduce flooding problems and strive 

for abatement of flood damage to houses and streets. 

• The City of Clearwater needs to continue to maintain, correct deficiencies and 

improve, where necessary, current levels of service. Maintenance and 
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improvement of the City Stormwater management system must be recognized as 

a service provided by the City on a regular and continuous basis. 

• Natural and man-made wetlands need to be utilized for stormwater storage and 

protected as natural resources. Wetlands provide a natural wildlife habitat and 

groundwater recharge functions which are pivotal characteristics of the natural 

and urbanized environment. 

• The City of Clearwater needs to research and develop new methods that are 

technically, environmentally, and economically viable of treating stormwater 

runoff before final discharge to improve and enhance local surface waters. 

Conservation Element

• The City shall continue to protect floodplains, drainage ways, and all other 

natural areas having functional hydrological characteristics. 

Recommendations.

With regards to level of service goals for drainage and flood protection, it is 

recommended that Policy 16.1.1 in the Comprehensive Plan be amended to coincide with 

the flood protection level of service (FPLOS) criteria adopted for the Stevenson Creek 

Watershed Management Plan. The primary FPLOS criterion is that there is to be no 

structural flooding (i.e., homes and businesses) for events up to and including the 100-

year flood. This criterion refers to the low floor slab elevation (lowest inhabited floor) as 

the point of structural flooding. This is consistent with FEMA/NFIP guidelines, and has 

been widely adopted by counties and municipalities across the state and the country. 

 The secondary set of FPLOS criteria specifies allowable thresholds for street 

flooding. The criteria is based upon residential, collector, and arterial roadways being 

passable for the 10, 25, and 100-year flood events, respectively. “Passable” is defined 

herein as 6” of flooding or less at the lowest edge of pavement in a travel lane. No 

flooding is allowable on hurricane evacuation routes for events up to and including the 

100-year flood. The following table summarizes the FPLOS criteria adopted for the 

Stevenson Creek Watershed Management Plan and the City of Clearwater: 
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Proposed Flood Protection Level of Service (FPLOS) Criteria 

FPLOS Category Allowable Flooding Depths 

1. Residential Streets, 2 lanes Up to 6” Allowed for 10-year flood 

2. Collector Roads, 2-4 lanes Up to 6” Allowed for 25-year flood 

3. Arterial Roads, 4 or more lanes Up to 6” Allowed for 100-year flood 

4. Hurricane Evacuation Routes No flooding up to 100-year flood 

5. Habitable Structures No flooding up to 100-year flood 

The above criteria is recommended for retrofit of existing City facilities that 

currently fall below the minimum levels of service. Due to varying levels of maintenance 

and the inevitable deterioration of public infrastructure over time, it is recommended that 

a safety factor be applied to all new stormwater management facilities serving new 

development within the City. The “safety factor” would help ensure these systems 

continue to function in the future at the minimum level of service, and could take the 

form of an additional 6” to 12” of freeboard applied to the minimum criteria stated above. 

With regards to reducing damages and losses due to flooding, it is recommended that 

Policy 16.3 be amended to include a provision that would allow the City, in cooperation 

with FEMA and/or SWFWMD, to consider the purchase, relocation, or floodproofing of 

flood-susceptible private properties in cases where it is not technically feasible or costeffective to reduce flood levels through infrastructure improvements. The purchases, 

relocations, and/or floodproofing should be done in cooperation with willing owners of 

flood-susceptible homes and businesses, and only after infrastructure improvement 

alternatives have been explored within an adopted watershed management plan. 

Community Development Code. 

The community development code for the City of Clearwater governs the design and 

construction of new development and re-development. The applicable divisions of this 

code include Division 7 – Erosion and Siltation Control, and Division 9 – General 

Applicability Standards. Within Division 9, the City of Clearwater Subdivision Design 
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Standards and Stormwater Drainage Criteria Manual is incorporated by reference. The 

Stormwater Drainage Criteria Manual specifies the methods to be used for calculating 

peak rates of runoff. This document includes a requirement for redevelopment of land 

upon which no stormwater treatment or attenuation facilities exist, whereby the 

redeveloper is required to provide “treatment of 1⁄2” of rainfall as applied to the entire area 

of a development project, and 1⁄2 inch as applied over the portion of the site plan 

undergoing alteration in the case of redevelopment.” The manual also specifies the use 

of a pre-redevelopment weighted runoff coefficient of 0.2 for a site that drains to an area 

of known flooding problems, and a coefficient of 1⁄2 of the actual calculated coefficient 

for a site that does not drain to an area of known flooding problems. This requirement 

results in a reduction in peak rates of runoff from sites undergoing redevelopment. These 

provisions exceed the requirements of the SWFWMD, which in many cases of 

redevelopment do not require any treatment or attenuation. 

Recommendations 

To ensure compliance with the recommended drainage and flood protection level of 

service goals stated at the beginning of this section, the City of Clearwater Subdivision 

Design Standards and Stormwater Drainage Criteria Manual should be amended to 

include the proposed FPLOS criteria, with an appropriate safety factor to be applied to 

new development. It is also recommended that possible changes to the Stormwater 

Drainage Criteria Manual be considered that would allow some flexibility in the methods 

used to calculate peak rates of runoff, such as allowing the SCS method in place of the 

rational method. This change would reduce any potential liability the City may be taking 

on be specifying the hydrologic methods to be used for private development, as these 

methods may not be the most applicable in all situations.

Municipal Code of Ordinances. 

The applicable portions of the City’s Code of Ordinances related to watershed 

management include the following chapters: 

Chapter 32. Utilities. Article VI. of this chapter governs Stormwater Management. 

This article establishes the legal framework for the City’s Stormwater Utility in 
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accordance with Florida Statute 403.0893, and establishes the stormwater utility fee 

structure. Additional articles in this chapter govern Sanitary Sewers, Water Supply, and 

Solid Waste. 

Chapter 33. Waterways and Vessels. Section 33.003 of Article I prohibits the 

placing, discharging, or depositing of sewage, trash, garbage, etc., into navigable waters. 

This includes the banks and shores of any tributaries where this material “is reasonably 

likely to be washed into such navigable waters, either by ordinary tidal actions or by the 

action of rain, floods or otherwise.” 

Chapter 47. Buildings and Building Regulations. Article I of this chapter specifies 

the methods and sources used to set the minimum floor elevations for new buildings or 

additions to existing buildings. 

Chapter 51. Flood Damage Prevention. This Chapter governs management of the 

floodplain within the City of Clearwater including adoption of floodplain mapping, and 

requirements for new development and building construction, including encroachments 

into designated floodplains and floodways. Adoption and enforcement of this ordinance 

is required for participation in FEMA’s National Flood Insurance Program (refer to 

Section 3.5-3). 

Recommendations

Dumping of yard waste into creeks, ditches, swales and even storm sewers is a fairly 

common practice throughout the Stevenson Creek Watershed (see Figure 3.5-1). This 

practice increases the workload of City maintenance crews, and degrades the quality of 

the stormwater by introducing nutrient-rich organic material to the system. When water 

levels and velocities rise due to heavy rainfalls, the material is washed into the Creek, and 

downstream where it ultimately deposits in the Stevenson Creek Estuary. The estuary 

has, in recent decades, become choked with highly organic sediments. Illegal dumping of 

yard waste has undoubtedly contributed to the accumulation of these sediments. 

Section 32.274 of the Code of Ordinances prohibit the placement of solid waste into 

any creeks, watercourses, storm sewers, and ditches, within the City and prohibits the 

placement of “waste materials of any kind...which impairs the proper operation of the 
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city’s sewer or drainage system”. Although these ordinances are interpreted to include 

lawn clippings, leaves, and fallen limbs, etc., such yard waste is not specifically 

mentioned in this portion of the Code. In order to facilitate the understanding and 

enforcement of this facet of the Code, it is recommended that “yard waste” be 

specifically included as a prohibited item. 

Figure 3.6-1 Yard waste (Oak leaves) dumped by a resident on the banks of 

Upper Stevenson Creek.

The City Should actively seek to educate its residents on the negative effects of the 

dumping of yard waste into its creeks, ditches, and storm sewers. If necessary, these 

education efforts should be followed by active enforcement of the applicable ordinances. 
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3.7 CAPITAL IMPROVEMENT COST ESTIMATES 

For purposes of budgetary planning, cost estimates were made, in 2001 dollars, of 

each recommended capital improvement project. The cost estimates are based on the 

conceptual design and are subject to change pending completion of a more detailed 

design process. Costs for most items were estimated based on past or current similar 

Parsons ES projects, and by consulting the FDOT 1- and 3-year cost history listings dated 

February 2001. Mobilization and demobilization costs were typically estimated to 

comprise approximately 9% of the total construction cost. 

Table 3.7-1 summarizes the total cost estimates for the individual projects, detailed 

estimates of which are included as Appendix H. The estimates include land acquisition, 

engineering and related services (surveying, environmental permitting, etc.), 

construction, and contingency. 

Cost estimates for acquisition of private property were based on the most recent 

assessed value as reported by the Pinellas County Property Appraiser’s Office, multiplied 

by a factor of 1.5 to include fair market value of the property plus legal fees. 

The magnitude and scope of the recommended improvements, coupled with 

budgetary constraints, will require phased implementation of the plan over a number of 

years. The capital costs listed in Table 3.7-1 will need to be adjusted annually for 

inflation, up to the year of actual construction, based on the construction price indices for 

the applicable year(s). In the next section, the recommended prioritization rankings are 

presented which will facilitate the development of an implementation schedule. 

 
Stevenson Creek Watershed Management Plan

Final Report

 Table 3.7-1. Stevenson Creek Watershed Management Plan Capital Cost Estimates

Project Estimated Capital Cost

No. Project Description (2001 dollars)

Spring Branch

1A.1 Spring Branch Conveyance Enhancements (Lower Portion) $526,115

1A.2 Spring Branch Conveyance Enhancements (Upper Portion) $960,703

1B Springtime Avenue and Douglas Avenue Bridges $830,830

1C Spring Branch Flood Detention Basin $2,634,542

1D Woodland Terrace Storm Sewer Replacement $446,783

1E Byram Pond Dredging and Expansion $831,636

1F Spring Branch Stabilization, Union Street to Byram Pond $933,969

1G Clearview Lake $620,212

1H Betty Lane Forested Habitat Preservation Site $1,100,000

 Subtotal (for alternative 2 - excluding project 1B) $8,053,960

Lower Stevenson

2A Palmetto Street Sediment Sump $544,546

2B N. Missouri Ave. and Palmetto St. Drainage Improvements $486,615

2C Installation of Additional CDS Units $526,500

2D Overbrook Avenue Detention Pond $1,755,860

Subtotal $3,313,520

Middle Stevenson

3A Glen Oaks Stormwater Detention Facility $2,203,240

Subtotal $2,203,240

Upper Stevenson

4A Hillcrest Avenue Overflow Bypass Culvert $2,299,109

4B Upper Stevenson Creek Stabilization $1,415,843

4C St Thomas Drive / Bellevue Boulevard Creek Restoration $1,801,913

 Subtotal $5,516,865

Hammond Branch

5A Flagler Drive / CSX Railroad North Swale Improvements $737,241

5B Palmetto Street Drainage Improvements $735,643

5C Saturn Avenue Drainage Improvements $303,382

5D Smallwood Circle Drainage Improvements $161,283

5E Lake Hobart Outfall Control Structure $14,300

Subtotal $1,951,848

Lk Bellevue Branch

6A Expansion of Lake Bellevue $1,337,884

6B Turner Street Box Culverts $1,554,761

Subtotal $2,892,645

Jeffords St Branch

7A Crest Lake Expansion $881,466

7B Duncan Avenue/Turner Street Detention Pond $1,494,952

7C Jeffords Street/Barry Road Detention Pond $1,690,634

Subtotal $4,067,053

Grand Total $27,999,132

 3.7-2 Table 3.7-1 Costs.xls
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SECTION 4.0 

WATERSHED MANAGEMENT PLAN 

PROJECT PRIORITIZATION 

 As stated in the introduction, the objectives of this Watershed Management Plan are 

to identify the causes of the problems of flooding, surface water quality degradation, 

excessive channel erosion, and loss of riparian habitat; and to identify, evaluate and 

recommend solutions to these problems. The problems and the causes of these problems 

were identified in Section 2.0. Recommendations for solutions to the problems were 

made in Section 3.0. This section serves to prioritize the improvements on the basis of 

benefits provided, cost effectiveness, and logical precedence. 

 The projects recommended in this document, whether considered singly or as a 

whole, are economically justifiable, and clearly in the interest of public safety, health, 

and welfare. The management plan is consistent with the laws of the federal, state and 

local government, and follows the policies outlined in State, regional, and local 

comprehensive plans. 

 In this section, projects that can be expected to provide the greatest overall benefit 

in the most cost effective manner are identified using a project ranking procedure. This 

management tool is a convenient and effective method of recommending priorities for the 

allocation of available funding. To help identify the priority projects in the Stevenson 

Creek Watershed Management Plan, a set of comparative evaluation criteria were 

identified, and a project ranking matrix was developed. The evaluation criteria selected 

as a means of grading the relative merits of the recommended master plan projects are 

discussed below. Within each category, individual projects were graded on a scale from 

0 to 10, with the lowest score indicating no real benefit and the highest indicating a high 

beneficial value. 

Flood Control Benefits. The relative flood control benefit of an individual project 

is a function of the number and type of Flood Protection Level of Service (FPLOS) 

deficiencies remedied by that project. The projects that rank the highest in this category 
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will either alleviate flooding over a large geographic area, or reduce flooding within a 

geographically concentrated large group of flood-susceptible homes and businesses. A 

score of one-half point was earned for each structure FPLOS deficiency and each 

residential street FPLOS deficiency remedied by the project. Remediation of each 

collector, arterial, and evacuation route FPLOS deficiencies earned scores of 1.0, 1.5, and 

2.0 points, respectively. The scores were summed for each individual project. Two 

projects, (3A) Glen Oaks, and (4A) Hillcrest Avenue Bypass, initially exceeded the 

maximum score of 10, and thus were assigned a score of 10. 

Water Quality Benefits. The relative water quality benefits of an individual 

project reflect the ability of the project to capture and remove pollutant loads from the 

stormwater runoff prior to discharge into downstream waterbodies. Those projects with 

little or no real water quality benefits receive a score of 0, while a project specifically 

designed to provide a high level of treatment of currently untreated stormwater runoff 

from a large drainage basin would receive a high score. In assigning scores in this 

category, the total suspended solids (TSS) and total nitrogen (TN) loads expected to be 

removed (lb./year) by each project were determined from the proposed conditions 

pollutant loading model. These removal rates were used as comparative indicators of 

relative water quality benefits. The project with the largest rate of pollutant removal 

(Glen Oaks), was assigned a score of 10, and the scores for the other projects are based 

on their individual pollutant removal rates, expressed as a fraction of the removal rates of 

the Glen Oaks Project. 

Ecological Benefits. The potential ecological benefits of individual projects are 

ranked based on evaluations of the anticipated improvements to wildlife habitat that will 

be realized after project construction. Factors such as the size of the affected area, 

current quality and ecological conditions, and proximity to other habitat areas are 

considered in the evaluation of benefits and the relative ranking. Areas that currently 

provide no habitat, but will provide significant habitat upon project completion, will rank 
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the highest in the matrix. Conversely, those projects which will have no habitat impacts, 

such as the replacement of culverts for flood control, will rank the lowest. 

Channel Erosion and Sedimentation Control Benefits. Projects which will have 

little or no effect in the remediation of channel erosion problems and sedimentation in the 

watershed are assigned a score of 0. Secondary benefits of projects that attenuate 

downstream peak discharge rates tend to reduce the potential for channel erosion, and 

therefore would earn the project a score of up to 5, depending on the magnitude of the 

attenuation and the proximity and severity of downstream erosion problems. Projects 

designed to permanently remedy severe channel erosion problems along a substantial 

length of channel would receive the highest ranking of 10. Projects that involve creation 

or expansion of maintainable sediment sumps on Stevenson Creek and Spring Branch 

would also receive a high score. 

Recreational and Educational Benefits. The recreational and educational 

benefits associated with a project are those that provide new opportunities for the general 

public by accommodating the placement of features such as picnic areas and shelters, 

trails and boardwalks, nature parks, fishing, boating, and/or interpretive exhibits. 

Projects that provide no new opportunities for recreational and educational benefits 

receive a score of 0, and those that can provide a high level of recreational and 

educational opportunity would be assigned a score of 10. 

Implementability. Implementability as a ranking criterion is an assessment of the 

relative severity of obstacles that must be overcome in order to construct the project. It is 

a cumulative assessment of factors such as property and easement acquisition 

requirements, permitting requirements, temporary impacts to nearby residences and 

businesses during construction, long-term maintenance and operation requirements, and 

relative ease of construction. A low ranking would be assigned to projects which would 

have a high degree of difficulty related to any or all of these issues. A high ranking 

would be assigned to a project with no foreseeable implementation concerns. 
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 Relative Benefits to Cost. As stated previously, all of the recommended projects 

of the Stevenson Creek Watershed Management Plan can be justified economically. 

However, because funding for public infrastructure improvements is not unlimited, it is 

useful to identify those projects that provide the most benefit for the least cost. In order 

to assign a score for this criterion, a total weighted benefits score was assigned to each 

project based on the sum of the weighted scores of the project in the five categories of 

flood control, water quality, ecological benefits, erosion control benefits, and 

recreational/educational benefits. The total benefit score was then divided by the 

preliminary cost estimate of the project in thousands of dollars. A multiplier was applied 

to the result to force an average score of 5.0, on a scale of 1 to 10, with 0 being the least 

cost effective and 10 being the most cost effective. A few projects earned scores greater 

than 10; these were subsequently reduced to 10. It should be noted that the result is not 

an actual benefit to cost ratio, but rather a relative measure of each project’s cost 

effectiveness compared to the other projects the plan. 

 While each of the listed ranking criteria is an important factor when evaluating the 

individual watershed management projects, it is not essential that each should have an 

equal weighting in the evaluation matrix. For that reason, weighting factors were 

assigned to each, ranging from 1 to 5, to establish the relative importance of individual 

ranking criteria. The following is a list of the weighting factors used: 

Ranking Criterion Weighting Factor 

Flood Control Benefits 5 

Water Quality Benefits 4 

Ecological Benefits 4 

Channel Erosion and Sedimentation Control Benefits 3 

Recreational and Educational Benefits 2 

Implementability 2 

Relative Benefits versus Cost 5 
Stevenson Creek Watershed Management Plan

Final Report

 Table 4-1. Stevenson Creek Watershed Management Plan Project Ranking Matrix

Flood Water Erosion Recreational/ Ability Relative

Control Quality Ecological Control Educational to Benefits Weighted

Project Benefits Benefits Benefits Benefits Benefits Implement vs. Cost Score Rank

No. Project Description 5 4 4 3 2 2 5

Spring Branch

1A.1 Spring Branch Conveyance Enhancements (Lower Portion) 10 1.5 0 10 0 6 10.0 5.7 3

1A.2 Spring Branch Conveyance Enhancements (Upper Portion) 6.5 0.5 0 0 0 8 4.2 2.8 14

1B Springtime Avenue and Douglas Avenue Bridges 1 0 0 0 0 7 0.7 0.9 28

1C Spring Branch Flood Detention Basin 1 5.7 10 5 2 4 3.9 4.4 6

1D Woodland Terrace Storm Sewer Replacement 2.5 0.1 0 0 0 9 3.4 1.8 22

1E Byram Pond Dredging and Expansion 1.5 0.8 0 5 0 4 3.6 2.0 21

1F Spring Branch Stabilization, Union Street to Byram Pond 0 0 0 10 0 10 3.8 2.6 16

1G Clearview Lake 0.5 0.9 0 1 0 8 1.7 1.3 27

1H Betty Lane Forested Habitat Preservation Site 0 0 10 0 6 3 5.5 3.3 12

Lower Stevenson

2A Palmetto Street Sediment Sump 0.5 0.2 2 9 0 4 10.0 3.7 9

2B N. Missouri Ave. and Palmetto St. Drainage Improvements 1 0.9 0 0 0 9 2.1 1.4 24

2C Installation of Additional CDS Units 0 4 1 0 0 10 4.4 2.4 18

2D Overbrook Avenue Detention Pond 2 1.8 6 0 4 6 3.3 3.0 13

Middle Stevenson

3A Glen Oaks Stormwater Detention Facility 10 10 10 5 10 6 8.8 8.5 1

Upper Stevenson

4A Hillcrest Avenue Overflow Bypass Culvert 10 0 0 3 0 6 3.0 3.3 10

4B Upper Stevenson Creek Stabilization 0 0 0 10 0 8 2.5 2.2 19

4C St Thomas Drive / Bellevue Boulevard Creek Restoration 9.5 0.4 6 2 2 3 5.4 4.5 5

Hammond Branch

5A Flagler Drive / CSX Railroad North Swale Improvements 5.5 0 0 2 0 4 5.3 2.6 17

5B Palmetto Street Drainage Improvements 2 0 0 2 0 8 2.5 1.7 23

5C Saturn Avenue Drainage Improvements 1 0.2 0 0 0 9 2.2 1.3 26

5D Smallwood Circle Drainage Improvements 1 0.1 0 0 0 6 3.9 1.4 25

5E Lake Hobart Outfall Control Structure 0 0.8 0 0 0 10 10.0 2.8 15

Lk Bellevue Branch

6A.1 Expansion of Lake Bellevue 4.5 8.7 7 1 3 8 9.7 6.1 2

6A.2 Upper Lake Bellevue Culverts 7.5 0 0 0 0 10 10.0 4.1 8

6B Turner Street Box Culverts 4.5 1.2 0 0 0 7 2.1 2.0 20

Jeffords St Branch

7A Crest Lake Expansion 2 1.6 6 1 4 10 6.8 4.1 7

7B Duncan Avenue/Turner Street Detention Pond 7 0.8 4 0 0 5 4.2 3.3 11

7C Jeffords Street/Barry Road Detention Pond 8 2.8 5 10 0 3 7.0 5.5 4

Table 4-1 Rankings.xls
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 The project prioritization ranking matrix for the Stevenson Creek Watershed 

Management Plan is presented in Table 4-1. It is noted that this ranking matrix evolved 

over time, with input from all the participating entities and the general public. 

 It should be stressed that the ranking process is, to a certain degree, a subjective 

process that is oriented towards personal values. It is, however, a valuable tool for 

screening projects and grouping them into relative priority classes. It is apparent through 

examination of Table 4-1 that those projects which serve multiple purposes rank the 

highest when compared to those with singular objectives. Also apparent is the 

observation that the projects that rank the highest generally have the highest scores in the 

relative benefits to cost category. 

Logical Precedence. Although not included as a ranking criterion per se, the 

successful implementation of the Stevenson Creek Watershed Management Plan will 

require consideration of the logical precedence, or order of construction of the individual 

projects. Many of the projects will rely on the prior completion of downstream 

improvements, in order to avoid creating unintended flooding impacts. Or, a project 

might not function at its intended full capacity unless constructed in conjunction with 

another nearby project. Within the Stevenson Creek Watershed Management Plan, four 

groups of projects were identified that require ordering by logical precedence. The four 

groups could be constructed in any order, however the projects within each group must 

follow the specified sequences. For comparison, the project rank is provided for each 

project in the sequence, within Table 4-2 below: 
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Table 4-2. Project Precedence 

Project Precedence 

Grouping 

Required Sequence of 

Construction 

Project Rank (Independent 

of Sequence) 

1. 1B or 1C 28 (1B), 6 (1C) 

2. 1A.1 3 

3. 1A.2 14 

Spring Branch Group 

4. 1G 27 

Glen Oaks Group 1. 3A 1 

2. 4A, 6B 10 (4A), 20 (6B) 

Hammond Branch Group 1. 5A 17 

2. 5C 26 

Lake Bellevue Group 1. 6A.1 2 

2. 6A.2 8 

 By examination of the Spring Branch Group in Table 4-2, it is apparent that 

construction of third-ranked project (1A.1) Spring Branch Improvements, Lower Portion, 

will require the prior construction of a lower-ranked project, either (1B) or (1C), in order 

to avoid downstream flooding impacts associated with the channel improvements. The 

preferred alternative, Project (1C) Spring Branch Detention Basin, is close in rank to 

project (1A.1) at a rank of 6. However, if Project (1C) cannot be implemented, for any 

reason, 28th-ranked Project (1B) Springtime Avenue and Douglas Avenue Bridges must 

be built instead. This raises the question of how to assign priorities to two projects with 

widely different ranks that must be built together. This could be resolved by re-assigning 

some of the flood control benefits from Project (1A.1) to (1B), until the scores of the two 

projects in Table 4-1 are equal. The resulting weighted score would be 3.8, which would 

result in an overall rank of 8 for the combined projects (1A.1 and 1B). The relative 

benefits to cost scores for projects (1A.1) and (1B) would change to 9.1 and 7.0, 

respectively. 

 In the remaining project precedence groups, the project precedence follows the 

order of the project rankings. Projects not specifically listed in the above table are 
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considered “stand alone” projects that could logically be constructed at any point during 

plan implementation. 

Public Acceptance. Public acceptance is a qualitative measure of the support for a 

particular project among the City’s taxpaying residents. In the early planning stages of a 

future public works project, public acceptance of the project can be difficult, if not 

impossible to gauge with any certainty. For this reason, it was not included herein as a 

ranking criterion. However, public involvement is a very important component of this 

plan; watershed improvements cannot be realized without the willingness and 

cooperation of residents within the watershed boundaries. For this reason, three (3) 

public meetings, or workshops, are being held to provide information and to receive 

comments and suggestions from the public. These comments and suggestions have 

helped to determine improvement projects and priorities. The first meeting was held in 

November of 1999, prior to the commencement of the project, to receive input from the 

public on known problems. A total of 68 questionnaires were received, containing 

descriptions by the residents of problems of sedimentation/erosion, water quality, and 

flood control. These questionnaires, along with the City’s complaint logs, were used to 

create a GIS map of the known problem areas, which was compared with the results of 

the computer modeling analyses by overlaying it on the 100-year floodplain map and the 

pollutant loading map. This information was then used in identifying areas to be targeted 

for watershed improvements. 

 The second meeting was held in January of 2001, where the results of the existing 

conditions analysis were presented along with the preliminary identified solutions for 

flood control, water quality, erosion and sedimentation. The residents were asked to 

comment in writing on the potential improvement projects. Approximately 70 residents 

attended, and 28 questionnaires were filled out. Most of the project-related comments 

received were positive, and many additional suggestions were made regarding specific 

components of the projects. These comments and suggestions were thoroughly reviewed 

and considered during the final completion of the Stevenson Creek Watershed 

Management Plan. Public meeting questionnaires from the first two public meetings are 
Stevenson Creek Watershed Management Plan 

Final Report 

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included as Appendix L of this report. A third public meeting is scheduled to be held 

later this year to present the completed Plan during a City Commission workshop, which 

will be televised city-wide. 

 Through the public meetings, workshops, and meetings among members of the 

project team, five projects were identified as potentially controversial projects. Project 

3A (Glen Oaks), although on City-owned property, will eliminate the existing golf course 

at that location, currently operated through a lease agreement by the non-profit Chi-Chi 

Rodriguez Foundation. Projects 4C (St. Thomas Drive to Bellevue Boulevard), and 7C 

(Jeffords/Barry Road Pond) were identified as potentially controversial projects due to 

the proposed acquisition of several residential properties. Projects 6A (Expansion of 

Lake Bellevue) and 7A (Crest Lake Expansion) were identified by the City Parks and 

Recreation Department as potentially controversial due to the proposed conversion of 

existing upland park areas to wetland habitat. 

 Winning public support for these projects through the City’s public information 

initiatives will be crucial to successful implementation of these projects. The final design 

and implementation of these projects must be sensitive to resident’s potential concerns 

regarding alternative recreational opportunities, the environment, safety, aesthetics, and 

property values. 
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SECTION 5.0 

REFERENCES AND BIBLIOGRAPHY

5.1 DRAINAGE, HYDROLOGY, AND FLOOD PROTECTION 

Reports

City of Clearwater 1997 Watershed Management Plan, Volume II. Post, Buckley, 

Schuh & Jernigan 

City of Clearwater Comprehensive Plan. May 18, 2000, City of Clearwater 

Planning Department. 

City of Dunedin Comprehensive Plan, City of Dunedin Planning Department 

Pinellas County Storm Drainage Basin Study Technical Appendix – Spring 

Branch of Stevenson Creek Basin and Coastal Zone 4 Basin. October 1981, 

Henningson, Durham & Richardson, Inc. 

Reducing Losses in High Risk Flood Hazard Areas: A Guidebook for Local 

Officials. 1985, Association of State Floodplain Managers 

Repetitive Loss Report – City of Clearwater, FL. October 1998, FEMA 

Summary Report for Stevenson’s Creek. August, 1988, W.K. Daugherty 

Consulting Engineers, Inc. 

Technical Information Prepared in Support of Request for Stevenson Creek 

FEMA Letter of Map Revision. May 1998, Camp, Dresser and McKee. 

Hydrologic and Hydraulic Models Documentation

FEMA, 1995. Guidelines and Specifications for Study Contractors. 

Shearman, J.O., Kirby, W.H., Schneider, V.R., and Flippo, H.N. U.S. Geological 

Survey, 1986. Bridge Waterways Analysis Model. USDOT/FHWA Research

Report No. FHWA/RD-86/106 

Singhofen, P.J., and Eaglin, L.M. 1995-2000. AdICPR User’s Manual, Version 

2.20.

USDA SCS, 1986. Technical Release 55, Urban Hydrology for Small 

Watersheds.
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Studies in Local Hydrology 

Broska, James C., Barnette, Holly L., 1999. Hydrogeology and analysis of aquifer 

characteristics in west-central Pinellas County, Florida. U.S. Geological Survey 

OF 99-0185. 

Gillen, Denis F., 1996. Determination of roughness coefficients for streams in 

west-central Florida. U.S. Geological Survey OF 96-226. 

Lopez, M.A., Michealis, D.M., 1979. Hydrologic data for urban watersheds in 

the Tampa Bay Area, Florida. U.S. Geological Survey WRI 78-125. 

Lopez, M.A., Woodham, W.M., Magnitude and frequency of flooding on small 

urban watersheds in the Tampa Bay area, west-central Florida. 1983. U.S. 

Geological Survey WRI 82-42. 

Trommer, J.T., Loper, J.E., Hammett, K.M., and Bowman, G., 1996. Comparison 

of estimated and observed stormwater runoff for fifteen watersheds in westcentral florida, using five common design techniques. U.S. Geological Survey OF 

96-129. 

Topography, As – Built Plans and Surveys

3rd Avenue Drainage Improvements Record Drawings. March 2000, City of 

Dunedin Department of Public Works and Utilities. 

City of Clearwater Stormwater Atlas. 1996-1999, City of Clearwater Public 

Works Administration, Engineering. 

City of Dunedin Stormwater Atlas. 1999, City of Dunedin Engineering Section 

Highland Avenue Stormwater Improvements As-Built Plans. November 1998, 

HDR Engineering, Inc. 

MSSW and ERP permit information on file with the Southwest Florida Water 

Management District (various files). 

Pinellas-Anclote Basin Aerial Photography with Contours. March 1977, May 

1979, and December 1985, Southwest Florida Water Management District. 

Spring Branch of Stevenson’s Creek Drainage Basin Field Survey Notes. March 

1979, Pinellas County Engineering Department. 
Stevenson Creek Watershed Management Plan 

Final Report 

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Stevenson Creek – Channel Improvements – Phase II Plans. March 1995, Camp, 

Dresser and McKee. 

Stevenson Creek Sediment Evaluation with Cross Sections. August 1999, City of 

Clearwater Public Works Administration, Engineering. 

Stevenson’s Creek Watershed Channel Improvements, Phase 1 As-Built Plans. 

February 1993, W.K. Daugherty Consulting Engineers, Inc. 

The Mall From Union Street to the South Terminus Record Drawings. July 1994, 

Seminole Engineering. 

Villas at Renaissance Square (Old Sunshine Mall) Construction Plans. January 

1999. Florida Design Consultants, Inc. 

5.2 WATER AND SEDIMENT QUALITY

Reports

City of Clearwater 1997 Watershed Management Plan, Volumes II and III. Post, 

Buckley, Schuh & Jernigan 

City of Clearwater City-Wide Surface Water Quality Technical Report, August 

1992-September 1995. Post, Buckley, Schuh & Jernigan, Inc. 

Stevenson Creek Estuary Preliminary Restoration Plan. October 2000, U.S. Army 

Corps of Engineers, Jacksonville District 

Stevenson Creek Sediment Characterization and Removal Feasibility Study, Final 

Report, August 1998. BCI Engineers and Scientists, Inc. 

Studies in Local Water Quality

Fernandez, M. and Hutchinson, C.B., 1993 Hydrogeology and Chemical Quality 

of Water and Bottom Sediment at Three Stormwater Detention Ponds, Pinellas 

County, Florida U.S. Geological Survey Water Resources Investigations Report 

92-4139 

Harper, H.H., Environmental Research and Design, Inc., 1994. Stormwater 

Loading Rate Parameters for Central and South Florida.

Kantrowitz, I.H., Woodham, W.M., 1995. Efficiency of a stormwater detention 

pond in reducing loads of chemical and physical constituents in urban 

streamflow, Pinellas County, Florida. U.S. Geological Survey WRI 94-4217. 
Stevenson Creek Watershed Management Plan 

Final Report 

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Lopez, M.A., Giovannelli, R.F., 1984. Water-quality characteristics of urban 

runoff and estimates of annual loads in the Tampa Bay area, Florida. U.S. 

Geological Survey WRI 83-4181. 

Raw Water Quality Data

 City of Clearwater Ambient Surface Water Monitoring Program, 1992-1995 

Environmental Data Report, Approximate 1⁄4 Mile Radius, Clearwater 

Brownfields Area Clearwater, Florida, 1999. Environmental Data Management, 

Inc. 

Marshall Street WWTP Parameter Monitoring Reports 1991-1999 

Pinellas County Ambient Surface Water Quality Monitoring Program, Pinellas 

County Department of Environmental Management 

Septic Tank Permit Database, 2000. Pinellas County Health Department 

Southwest Florida Water Management District, Lake Bellevue Monitoring 

Program, 1996-1997 

5.3 NATURAL RESOURCES 

Internet sites

Audubon - Florida Audubon Society http://www.audubon.usf.edu/audubon1.htm

Florida Cooperative Extension Service http://www.wec.ufl.edu/

Florida Cooperative Extension Service-Wildlife Extension 

http://www.wec.ufl.edu/extension/

Florida Fish and Wildlife Conservation Commission - Homepage 

http://www.state.fl.us/fwc/

Florida Fish and Wildlife Conservation Commission - Florida's Endangered 

Species, Threatened Species And Species Of Special Concern 

http://fcn.state.fl.us/gfc/pubs/endanger.html

Florida Fish and Wildlife Conservation Commission - Publications 

http://www.state.fl.us/fwc/pubs/pubs.html

Florida Museum of Natural History http://www.flmnh.ufl.edu/
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Florida Natural Areas Inventory - Species and Natural Community Summary for 

Hillsborough County http://www.fnai.org/HILL-SUM.HTM

The Nature Conservancy http://www.tnc.org/ 

The Nature Conservancy http://www.tnc.org/frames/index.html?/html/list.html

University of Florida EDIS http://edis.ifas.ufl.edu/

USEPA Surf Your Watershed http://www.epa.gov/surf/

USFWS Region 4 http://southeast.fws.gov/

USFWS Biological and Natural History Information 

http://refuges.fws.gov/NWRSFiles/WildlifeMgmt/SpeciesAccounts/SpeciesAccou

ntsIndexBirds.html

USFWS Endangered Species Homepage http://endangered.fws.gov/endspp.html

U.S. Natural Heritage Programs: Florida Natural Areas Inventory 

http://www.fnai.org/

Printed Material

Ashton, Ray E. 1996. Rare and Endangered Biota of Florida. Volume V. Birds. 

University Press of Florida, Gainesville. 

Exotic Pest Plant Council, 1997. List of Florida’s Most Invasive Species. EPPC 

Committee on Invasive Species. 

Florida Natural Areas Inventory, 1990. Guide to the Natural Communities of 

Florida. FNAI and the Florida Department of Natural Resources. 

Gilbert C.R. - Editor. Rare and Endangered Biota of Florida Volume II Fishes,

1992. 

Humphrey, Stephen R. 1992. Rare and Endangered Biota of Florida. Volume I. 

Mammals. University Press of Florida, Gainesville. 

Kale, H.W. II, and D.S. Maehr. Florida's Birds - A Handbook and Reference, 

1990. 

Moler, Paul E. 1992. Rare and Endangered Biota of Florida. Volume III 

Amphibians and Reptiles. University Press of Florida, Gainesville. 
Stevenson Creek Watershed Management Plan 

Final Report 

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Rodgers J.A. Jr., H.W. Kale II, and H.T. Smith - Editors. Rare and Endangered 

Biota of Florida Volume V Birds, 1996. 

USFWS, 1999.. South Florida Multi-Species Recovery Plan. Vero Beach Office, 

Florida 

USFWS, 1989. Florida Manatee Recovery Plan., Atlanta, Georgia. 

USFWS, 1997. Endangered and Threatened Wildlife and Plants, Federal 

Register 50 CFR 17.11 and 17.12. 

Wunderlin, Richard P., Bruce F. Hansen, and Edwin Bridges, 1998. Atlas of 

Florida Vascular Plants. Institute for Systematic Botany, University of South 

Florida. 

Personal Communications

Lane, Geof, director, Clearwater Marine Aquarium. 

Williams, Jane, member, Clearwater Audubon Society. 
1 

Final Report 

Bacterial Source Tracking Using Antibiotic Resistance 

Analysis of Fecal Coliforms 

Stevenson Creek, Clearwater, Florida 

June – December, 2000 

Valerie J. Harwood and John E. Whitlock 

University of South Florida 

Department of Biology

(vharwood@chuma1.cas.usf.edu) 

March 20, 2001 
 2

Introduction 

Various bacteria are found in the digestive tracts and feces of wild and domestic animals and humans. 

Some of these bacteria including fecal coliforms and fecal streptococci are used as indicators of fecal 

contamination when present in natural waters. Unfortunately, the mere presence of these indicator bacteria 

is not informative as to the source of fecal pollution, an important factor for risk-assessment and 

remediation. Consequently, several methods collectively known as bacterial source tracking (BST) 

methods have been developed to “fingerprint” fecal indicator bacteria in order to determine their host or 

source (e.g. human, dog, wild animal) and may be based on either the genetic make-up of the bacteria, or 

on physiological characteristics such as resistance to various antibiotics. Using antibiotic resistance 

analysis (ARA), it is possible to assess the source of indicator organisms based on a much larger subset of 

the bacterial population than is currently possible using genetic methods. ARA was used to determine the 

source of fecal contamination in this study essentially as described in Harwood et. al 2000. 

In any BST method, a database of fingerprints, or patterns, of bacteria isolated from the feces of known 

source animals (e.g. humans, dogs, wild animals) must first be constructed and tested for its predictive 

accuracy. This database is called the calibration data set. Discriminant analysis, a multivariate statistical 

test, is used to analyze the data. The ability of the database to accurately predict the source of indicator 

organisms is assessed using isolates from known sources as “unknown” or test isolates. The database can 

also be self-crossed, that is, the database isolates are used as both the calibration data set and the test data 

set. 

The database used in this study consists of 3309 fecal coliform isolates from six sources, humans (domestic 

wastewater), dogs, cattle, chickens, pigs and wild animals (mainly raccoons and birds). The average rate of 

correct classification (ARCC) is a measure of the predictive accuracy of the database, and is obtained by 

self-crossing the database, adding the number of correctly classified isolates in all source categories, and 

dividing by the total number of isolates. The ARCC of this data set is 57.2% when 6 source categories are 

used in the analysis. The chance of an isolate falling into one of 6 categories by chance if categorization 

were random is 16.7%, therefore the antibiotic resistance patterns of fecal coliforms have substantial 

predictive capacity with respect to bacterial sources (Harwood et al., 2000). 

In any database, some percent of isolates from other sources will misclassify as human isolates. The rate of 

misclassification of isolates into the human category can be used to develop a cut-off point for significant 

levels of human isolates. In this database, about 20% of wild animal isolates are misclassified as human, 

and wild animal isolates have the highest rate of misclassification as human of all sources. The 

conservative rate of 25% is used as the cut-off point for identification of a significant percentage of isolates 

from human sources in any sample. 

Stevenson Creek 

This study was initiated in order to identify the dominant source(s) of fecal contamination to Stevenson 

Creek in Clearwater, Florida. Five sites were chosen to represent areas where routine monitoring has shown 

high levels of fecal coliforms. Two of the sites were located at the composite samplers previously installed 

for the project (Comp1 and Comp2). Comp1 is located at the golf course on the main branch of Stevenson 

Creek; Comp 2 is located on Spring Branch off King Highway. Sites previously designated for monitoring 

efforts were sampled: STC1 at Spring Branch, STC2 at Hammond’s Branch and STC5 at Evergreen. 

Sampling dates were June 27, July 25, August 22, September 19, October 23, November 13, and December 

27, 2000. Isolation of fecal coliforms was poor from November with samples yielding only an estimate of 

population density and no information as to source of contamination. Consequently, additional samples 

were collected in December. 
 3

Results 

The dominant sources of fecal coliform isolates obtained from the five sites over the course of this study 

were wild animal, dog and human. The overall trend was for wild animal isolates to comprise the majority 

of fecal coliforms obtained when colony forming units (CFU) counts exceeded the acceptable limit of 

200CFU/100ml. STC1 and STC2 sampled on 6/27/00 were the only observations where exceedingly high 

CFU counts co-occurred with a majority of human isolates. On 8/22/00 at STC1, the majority of isolates 

were dog and the CFU count was 300/100ml. Samples from the month of September yielded a majority of 

human isolates from all sites while densities of coliforms were low, ranging from 7-26 CFU/100ml. The 

above results suggest that source most frequently contributing to excessive fecal coliform counts was wild 

animals followed by human and dog isolates. 

Some statistically significant relationships were apparent between the CFU counts and classification of 

isolates. The percentages of isolates from specific sources were compared to CFU/100ml using a regression 

analysis. There was a significant, inverse relationship between the percentage human isolates and the CFU 

count for Comp2, i.e. as the CFU count went down over the study period, the percentage of human isolates 

went up , P=0.019, r2

= 0.87 (Fig. 9). While this relationship was not observed for the other four sites 

examined individually, it was observed when data from all sites were pooled, P=0.001, r2

=0.34 (Fig 11). 

This indicates enough of an overall trend among the sites to maintain a significant inverse relationship 

between CFU and percent human. Likewise, when the percentage of wild isolates was compared to CFU 

counts in a similar test, a significant direct relationship was observed at STC 1, P<0.001, r2

= 0.96. The 

CFU count decreased along with the percent of wild isolates, Fig 10. Again, a significant relationship was 

not observed for any of the other four sites when examined individually. However, when the five sites 

were pooled the regression was significant, P<0.001, r2

=0.60 (Fig. 12). These results support the notion 

that wild animals are the predominant contributors to fecal contamination marked by elevated fecal 

coliform levels. 

The relative importance of specific wild animals as contributors to high fecal coliform numbers is difficult 

to assess with confidence but is likely related to factors such as population size and density and their 

utilization of the territory adjacent to the sample sites. During the course of the study, birds were the most 

frequently observed wild vertebrates. Great white egrets, snowy egrets, little blue herons, and anhingas 

were frequently present in low densities during sample collection i.e one or two individuals. Waterfowl 

such as gallinules, coots and ducks, were observed in slightly higher densities (three or four individuals), 

but not as frequently. The largest aggregates of wild animals observed during the study period were flocks 

of migratory birds such as European starlings and boat-tailed grackles. These birds, however, were 

observed during the late fall months when fecal coliform densities were low. Gulls common to the coastal 

areas such as the black-headed gull and herring gull were not observed frequently near the sampling sites. 

While human input may not be the major cause of elevated fecal coliform levels for most of the samples 

analyzed for this study, the domination of small populations by human isolates suggests that human sources 

contribute to low-level background contamination. This occurs when FC populations are low, near the 

transition to dry season and perhaps few isolates are washed into surface waters from draining storm water. 

Lowering water tables may also draw wastewater from small, otherwise innocuous leaks. Overall, there 

was little evidence of acute human fecal contamination on a large scale across the five site examined. 

However, there may be considerable human source influencing STC1 and STC2, which is detectable 

despite the presence of fecal coliforms from other sources. These sites were impacted by human fecal 

sources with the highest frequency and magnitude of the five sites. They were more frequently over 25% 

human and exhibited a higher mean % human than the other sites. The most pronounced human 

contamination of STC1 and 2 occurred in June where 56.7% and 47.7% of isolates examined were human. 

The density of human isolates at STC1 and STC2 may be approximated from the fecal coliform density 

using the percent classified as humans. This yields 11400 ‘human’CFU/100ml for STC1 and 2400 

‘human’CFU/100ml for STC 2, both of which exceed the limit of 200CFU/ml. Consequently, unlike any 

other sampling event in this study, the human input for these two sites in June were high enough to cause 

violation considering only human isolates. 
 4

References 

V. J. Harwood, J. Whitlock and V. H. Withington. 2000. Classification of the antibiotic resistance patterns 

of indicator bacteria by discriminant analysis: use in predicting the source of fecal contamination 

in subtropical Florida waters. Appl. Environ Microbiol. 66:3698-3704.
5 

Table 1. Density of fecal coliforms from the five sites as determined by membrane filtration 

Colony Forming Units/100ml 

Site June July August September October November December 

STC 1 20000 13000 300 26 35 1 6 

STC 2 5000 2200 68 7 1 1 70 

STC 5 1600 6400 115 7 1 1 24 

Comp 1 12000 18000 110 9 6 30 17 

Comp 2 20000 12000 0 16 960 10 120 

Mean 11720 10320 118.6 13 200.6 8.6 47.4 

Table 2. Percent wild isolates at Stevenson Creek sites, June – December 

Site June July August Sept Oct Nov Dec Mean 

Comp1 100.0 62.7 76.2 0 34.1 NA 0 45.5 

Comp2 100.0 62.1 30.5 0 63.4 NA 0 42.7 

STC1 43.3 42.1 21.7 3.1 0 NA 0 18.9 

STC2 40.9 43.2 10.5 16.7 NA NA 0 22.3 

STC5 80.6 67.7 46.7 6.3 NA NA 0 40.3 

Table 3. Percent human isolates at Stevenson Creek sites, June – December 

Site June July August Sept Oct Nov Dec Mean # > 25%

Comp1 0 3.7 4.8 62.5 20.5 NA 75 27.8 2 

Comp2 0 6.9 25.4 93.3 15.9 NA 90.5 38.7 3 

STC1 56.7 31.6 13.3 90.6 12.5 NA 71.4 46.0 4 

STC2 47.7 16.2 10.5 83.3 NA NA 75 46.5 3 

STC5 0 22.6 10 75 NA NA 82.5 38.0 2 

Table 4. Percent dog isolates at Stevenson Creek sites, June – December 

Site June July August Sept Oct Nov Dec Mean 

Comp1 0 0 19.1 37.5 36.4 NA 25 19.6 

Comp2 0 0 42.4 6.7 2.3 NA 9.5 10.15 

STC1 0 18.4 65.0 3.1 87.5 NA 28.6 33.7 

STC2 0 18.9 79.0 0 NA NA 25 24.6 

STC5 0 6.5 43.3 18.8 NA NA 17.5 17.2 
6

Density of Fecal Coliforms for Each of Five Sites Over Seven Months

0

5000

10000

15000

20000

June July August September October November December

Month

Colony Forming Units per 100ml

STC 1

STC 2

STC 5

Comp 1

Comp 2

Figure 1. CFU/100ml from the five sites over seven months. 

Density of Fecal Coliforms for Each of Five Sites Over Seven Months

1

100

10000

June July August September October November December

Month

Colony Forming Units per 100m

STC 1

STC 2

STC 5

Comp 1

Comp 2

Figure 2. CFU/100ml from the five sites over seven months, graphed on a log scale. 
7

Figure 3 

Figure 4. 

Categorization of Isolates from Each of Five Sites on 6/27/00

0

20

40

60

80

100

120

Comp1 Comp2 STC1 STC2 STC5

Sites

Percentage of Isolates Classified into each Source

% human

%wild

% dog

Categorization of Isolates from Each of Five Sites on 7/25/00

0

10

20

30

40

50

60

70

80

Comp1 Comp2 STC1 STC2 STC5

Sites

Percentage of Isolates Classified into each Source

% human

%wild

% dog
 8

Figure 5. 

Figure 6. 

Categorization of Isolates from Each of Five Sites on 8/22/00

0

10

20

30

40

50

60

70

80

90

Comp1 Comp2 STC1 STC2 STC5

Sites

Percentage of Isolates Classified into each Source

% human

%wild

% dog

Categorization of Isolates from each of Five Sites on 9/19/00

0

10

20

30

40

50

60

70

80

90

100

Comp1 Comp2 STC1 STC2 STC5

Site

Percentage of Isolates Classified into each Sourc

% human

%wild

% dog
9 

Figure 7. 

Categorization of Isolates from the Three Sites from Which Fecal Coliforms were Obtained on 

10/23/00

0

10

20

30

40

50

60

70

80

90

100

Comp1 Comp2 STC1 STC2 STC5

Sites

Percentage of Isolates Classified into each Source

% human

%wild

% dog

Categorization of Isolates from Each of Five Sites on 12/27/00

0

10

20

30

40

50

60

70

80

90

100

Comp1 Comp2 STC1 STC2 STC5

Sites

Percentage of Isolates Classified into each Category

% human

%wild

% dog

Figure 8. 
 10

Monthly Observations from Comp2 Plotted as % Human vs Log CFU/100ml

-20

0

20

40

60

80

100

120

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Log CFU/100ml

% Human

Figure 9. 

Monthly Observations from STC 2 Plotted as % Wild vs Log CFU/100ml

-20

-10

0

10

20

30

40

50

60

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Log CFU/100ml

% Wild

Figure 10.