3/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 217 

## Appendix 1 A : Methods and Tools for Controlling Stormwater 1 

## Runoff (Quantity and Quality) 2

1 This appendix describes various methods, including guidance manuals, and tools for controlling 3 stormwater runoff. This appendix includes: 4
1 A .1 Methods and Manuals 5
1 A .2 Complex Models 6
1 A .3 Simpler Models (largely spreadsheet-based or onl ine) 7



### A. 1

. 1 Methods and Manuals 8 Nationally-Applicable LID Design Methods and Manual s Prince George’s County, Maryland, Low-Impact Develo pment Design Strategies: An Integrated Design Approach, EPA 841-B-00-003, 2000. Prince George’s County, Maryland, Low-Impact Development Hydrologic Analysis , EPA 841-B00-002, 2000. www.epa.gov/nps/lid U.S. EPA, Stormwater Best Management Practices Design Guide , Office of Research and Development, EPA/600/R-04/121, Volumes 1-3 (121, 12 1A, 121B), September 2004. www.epa.gov/nrmrl/pubs/600r04121/600r04121.htm
Center for Watershed Protection Urban Subwatershed Restoration Manual Series ( www.cwp.org/Store/usrm.htm )
Center for Watershed Protection Managing Stormwater in Your Community: A Guide for Building an Effective Post-Construction Program ( www.cwp.org/Resource_Library/Center_Docs/SW/pcguida nce/Manual/PostConstructionManual.pdf ) Water Environment Research Foundation (WERF). Decentralized Stormwater Controls For Urban Retrofit And Combined Sewer Overflow Reductio n www.werf.org/AM/Template.cfm?Section=Search&Templat e=/CustomSource/Research/ ResearchProfile.cfm&ReportId=03-SW-3&CFID=2715758&C FTOKEN=75805127
WERF. Critical Assessment of Stormwater Treatment and Con trol Selection Issues . In Publication. Geosyntec Consultants and Wright Water Engineers. Urban Stormwater BMP Performance Monitoring . 2009. www.bmpdatabase.org/MonitoringEval.htm The Low-Impact Development Center, www.lowimpactdevelopment.org ; several LID manuals

93/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 218 Federal Facility Design Manuals Technical Guidance on Implementing the Stormwater R unoff Requirements for Federal Projects under Section 438 of the Energy Independence and Se curity Act, USEPA, 2009, EPA 841-B-09- 001, December 2009, www.epa.gov/owow/nps/lid/section438 U.S. Naval Facilities Engineering Command, Low Impact Development, Draft, Unified Design Criteria , UFC 3-210-10, October 2004. www.wbdg.org/ccb/DOD/UFC/ufc_3_210_10.pdf U.S. Department of Housing and Urban Development, The Practice of Low Impact Development , 2003, www.huduser.org/portal/publications/destech/lowImpa ctDevl.html U.S. Army Corps of Engineers. Low Impact Development for Sustainable Installation s: Stormwater Design and Planning Guidance for Develop ment within Army Training Areas

. Public Works Technical Bulletin 200-1-62. October 2 008.

1 Transportation-focused LID Design Methods and Manua ls Low Impact Development Center, Inc., 2006, GeoSynte ch Consultants, University of Florida, Oregon State University, Evaluation of Best Management Practices for Highway Runoff Control, Report N. 565 for National Cooperative Highway Rese arch Program (NCHRP), Project 25-20 (1). http://onlinepubs.trb.org/Onlinepubs/nchrp/nchrp_rp t_565.pdf

2 Example State/Local Design Manuals and Resources (a lso refer to individual practice fact sheet references) The Chesapeake Stormwater Network. Baywide BMP Design Specifications

. www.chesapeakestormwater.net/baywide-design-specifi cations2 Pennsylvania. Stormwater BMP Manual . 2006. www.elibrary.dep.state.pa.us/dsweb/View/Collection- 8305
Delaware. Standards & Specifications for Green Technology BMP s . 2005. www.dnrec.state.de.us/DNREC2000/Divisions/Soil/Stor mwater/New/GT_Stds%20%26%20Spe cs_06-05.pdf
District of Columbia. Stormwater Guidebook. http://ddoe.dc.gov/ddoe/frames.asp?doc=/ddoe/lib/dd oe/stormwaterdiv/2009.05.07_SWM_Table _of_Contents.pdf North Carolina Coastal Federation, www.nccoast.org , resources on implementing LID to protect shellfish beds and coastal beaches.
U.S Fish a nd Wildlife Service, Bayscapes , U.S Fish and Wildlife Service, Bayscapes , w ww.fws.gov/ChesapeakeBay/Bayscapes.htm

33/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 219 BMP Performance Information Water Environment Research Foundation. Internationa l Stormwater BMP Database. www.bmpdatabase.org
EPA. Urban BMP Performance Tool. www.epa.gov/npdes/urbanbmp Center for Watershed Protection. National Pollutant Removal Performance Database. www.cwp.org/Resource_Library/Controlling_Runoff_and _Discharges/sm.htm

1 Source Control and Pollution Prevention Manuals U.S. EPA National Management Measures to Control Nonpoint So urce Pollution from Urban Areas Office of Oceans, Wetlands and Watersheds , EPA-841B-05-004, December 2005 ( www.epa.gov/owow/nps/urbanmm/ )
US EPA The Use of Best Management Practices (BMPs) in Urba n Watersheds, Office of Research and Development, EPA/600/R-04/184, Septemb er 2004.
Center for Watershed Protection Urban Subwatershed Restoration Manual Series, Volum e 8,Pollution Source ControlPractices, February 2007 ( www.cwp.org/Store/usrm.htm ) Managing Storm Water Runoff to Prevent Contaminatio n of Drinking Water and Managing Highway Deicing to Prevent Contamination of Drinkin g Water. Steve Ainsworth, USEPA



### 1 A .2 Complex, LID-capable Models 2 Publicly Publically

- available models appropriate for evaluating LID pra ctices include: 3

• EPA’s U.S. EPA's Storm Water Management Model, version 5 (SWMM5), 4

• EPA’s U.S. EPA's Hydrologic Simulation Program - FORTRAN model (HSP F), and 5

• U.S. Army Corps of Engineers, Hydrologic Engineerin g Center – Hydrologic Modeling 6 System (HEC-HMS) 7

• Western Washington’s Hydrology Model, version 3 (WW HM3). 8

• University of Wisconsin, Civil & Environmental Engi neering Department, Water 9 Resources Group - RECARGA 10 The following summarizes these complex, LID-capable models: 11



### U.S. EPA's Storm Water Management Model, version 5 (SWMM 5) 12 EPA’s The US EPA Storm Water Management Model (SWMM) is a dynamic r ainfall-runoff 13 simulation model used for single event or long-term (continuous) simulation of runoff quantity 14 and quality from primarily urban areas. SWMM5 divid es the water balance process into four 15 compartments: ( 1) atmosphere (precipitation); ( 2) land surface (divides precipitation into 16 infiltration, storage, or runoff; ( 3) groundwater; and ( 4) transport (pipe and channel flow, as well 173/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 220 as storage). It can perform both single event and l ong-term continuous simulation using 1 precipitation data recorded at hourly or less inter vals. These inputs can be supplemented with 2 monthly evaporation data and daily temperature read ings. Different hydraulic routing techniques 3 are available to manage from simple to complex rout ing conditions. Infiltration can be simulated 4 using Horton, Green-Ampt, or Curve Number technique s. These techniques vary in complexity 5 and the availability of the parameters used for the ir estimation. They can take into account initial 6 soil moisture conditions, hydraulic conductivity, s oil moisture capacity, and its regeneration. 7 Separate accounting is provided for runoff from per vious areas and impervious areas, and routing 8 of runoff from one area over another is possible. S WMM5 can simulate pollutant build-up, 9 washoff, and treatment, although these capabilities are not needed to determine predevelopment 10 hydrology comparisons. 11 SWMM5’s advantages are that it uses physically-base d process models and input parameters 12 wherever possible, it can model any number of stora ge- or infiltration-based BMPs, it contains 13 robust procedures for routing runoff flow, and it a llows models to be built to any level of spatial 14 detail needed to provide the most accurate water ba lance for a site. A disadvantage is that it does 15 not currently have the capability to model some BMP s the employ infiltration, storage, and/or 16 flow routing in combination with one another (such as infiltration ponds and vegetated swales). 17 This model has been in use since 1971, and has sinc e undergone several major upgrades since its 18 inception, including expansion of LID applications in 2009. The following applications are 19 discussed in the 2009 manual: 20 1. Post-Development Runoff. 21 2. Surface Drainage Hydraulics. 22 3. Detention Pond Design 23 4. Low Impact Development 24 5. Runoff Water Quality. 25
6. Runoff Treatment 26 7. Dual Drainage Systems. 27 8. Combined Sewer Systems. 28
9. Continuous Simulation 29 The model and supporting documentation are availabl e at 30 www.epa.gov/ednnrmrl/models/swmm/index.htm

. 31



### U.S. EPA’s Hydrological Simulation Program Fortran (HSPF ), and WinHSPF 32 WinHSPF has broad capabilities for hydraulic, hydro logic, and water quality modeling. BMPs 33 are modeled as either “reaches” that can represent channels or areas of storage, or as “pervious 34 land”. WinHSPF can be used for a single rain event or continuous simulation. In WinHSPF, only 35 the “pervious land” module can be used for infiltra tion. Infiltration can vary with time as soil 363/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 221 moisture conditions change, and spatial variability in infiltration rates can be addressed. The 1 advantages of WinHSPF include the very broad capabi lities for simulating infiltration, surface 2 runoff, groundwater movement, evaporation and evapo transpiration, snowmelt, and for water 3 quality parameters, including temperature (a requir ement of Section 438). Another advantage is 4 that it has been incorporated into BASINS, an EPA m odel that takes advantage of the capabilities 5 of GIS and other systems. 6 Disadvantages of WinHSPF are its complexity and its limited routing capability compared to 7 SWMM5. 8 It is the only comprehensive model of watershed hyd rology and water quality that allows the 9 integrated simulation of land and soil contaminant runoff processes with in-stream hydraulic and 10 sediment-chemical interactions. The user must input continuous rainfall records to drive the 11 runoff model. Additional records of evapotranspirat ion, temperature, and solar intensity can be 12 imported for more accurate results. A large number of model parameters can be specified 13 although default values are provided where reasonab le values are available. The result of this 14 simulation is a time history of the runoff flow rat e, sediment load, and nutrient and pesticide 15 concentrations, along with a time history of water quantity and quality at any point in a 16 watershed. 17 The model and supporting documentation are availabl e for download at 18 www.epa.gov/ceampubl/swater/hspf

. 19



### HEC-HMS 20 HEC-HMS replaces HEC-1 by building on the original capability of simulating precipitation21 runoff and routing processes. HEC-HMS added capabil ities for distributed modeling and 22 continuous simulation. HEC-HMS includes a broad sel ection of models for representing rainfall 23 distributions, computing runoff volume (i.e. differ ent selections of infiltration and losses 24 algorithms), for modeling direct runoff (overland f low and interflow); baseflow in a stream; and 25 channel flow. It is capable of modeling either even t-based or continuous simulations. 26 HEC-HMS uses three major components in analyzing a hydrologic system: 27 1. Basin model – user-entered data on basin data, incl uding losses characteristics and 28 connectivity. 29 2. Meteorological model – user-entered data on rainfal l, snowmelt, and evapotranspiration 30 rate. 31 3. Control specifications – user-entered calculation i ntervals 32 Precipitation considerations include areal and temp oral distribution, and use of radar data. 33 Evapotranspiration and precipitation are represente d in the soil-moisture accounting (SMA) 34 model and enables modeling of the drying of the wat ershed, or otherwise movement of water, 35 between rainfall events for continuous modeling. A five-layer model is used: canopy, surface, 36 soil, upper groundwater, and lower groundwater. Alt ernatively, there is a deficit-constant method 37 that simplifies to a one-layer model for soil. HEC- HMS divides surfaces into either directly 38 connected impervious areas or pervious surfaces. Lo sses on the pervious surfaces include 393/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 222 interception, infiltration, storage (consisting of canopy, surface, soil-profile, and groundwater), 1 evaporation and transpiration. 2 HEC-HMS is widely used for simulating distributed i nfiltration controls, particularly when 3 interactions with streams (with potentially varying baseflows or flash-flows) or input into 4 subsequent river analysis is desired, via HEC-RAS. HEC-HMS also includes extensive elements 5 for modeling engineered structures in management sy stems for reservoirs, dams, pumps, and 6 other structures. 7
This model is available for download at 8 www.hec.usace.army.mil/publications/pub_download.ht ml 9



### WWHM3 10 WWHM3 is the third edition of the Western Washingto n Hydrology model developed for 11 Washington State Department of Ecology, with input parameters unique for that region. The 12 model is built on a continuous simulation HSPF plat form and can model the entire hydrological 13 cycle for multiple years. The purpose of the WWHM3 is to size stormwater control facilities to 14 mitigate the effects of increased runoff (peak disc harge, duration, and volume) from proposed 15 land use changes that impact natural streams, wetla nds, and other water courses. WWHM3 also 16 uses an “LID Scenario Generator” to show the mean a nnual distribution of stormwater into 17 surface runoff, interflow, groundwater, and evapotr anspiration. Using the LID Scenario 18 Generator, the user can change land use combination s to optimize performance. In addition to 19 LID Scenario Generator, the user can explicitly mod el various LID practices, including green 20 roofs. 21 The software has been used to develop stormwater sy stems for the 19 counties in western 22 Washington State and is designed to comply with the CWA (NPDES Phase I and II), the 23 Endangered Species Act and State and local stormwat er regulations. More information can be 24 found at 25 www.ecy.wa.gov/Programs/wq/stormwater/wwhmtraining/ wwhm/wwhm_v3/index.html

. 26



### RECARGA 27 The RECARGA model was developed by the University o f Wisconsin Civil & Environmental 28 Engineering Department Water Resources Group to pro vide a design tool for evaluating the 29 performance of bioretention facilities, raingarden facilities, and infiltration basins. Individual 30 facilities with surface ponding, up to 3 distinct s oil layers and optional underdrains can be 31 modeled under user-specified precipitation and evap oration conditions. The model continuously 32 simulates the movement of water throughout the faci lity (ponding zone, soil layers and 33 underdrains), records the soil moisture and volume of water in each water budget term 34 (infiltration, recharge, overflow, underdrain flow, evapotranspiration, etc.) at each time step and 35 summarizes the results. The results of this model c an be used to size facilities to meet specific 36 performance objectives, such as reducing runoff vol ume or increasing recharge, and for 37 analyzing the potential impacts of varying the desi gn parameters. Information is available at 38 http://dnr.wi.gov/runoff/stormwater/technote.htm

. 393/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 223 

### 1 A .3 Simpler Models 1 The following summarizes several simpler, spreadshe et-based or online, models: 2 

### Virginia Runoff Reduction Method Spreadsheets 3 The “Runoff Reduction Method” is a system that inco rporates site design, stormwater 4 management planning, and BMP selection to develop t he most effective stormwater approach for 5 a given site. The method relies on a three-step com pliance procedures that includes 1) applying 6 site design practices to minimize impervious cover, grading and loss of forest cover, 2) apply 7 runoff reduction practices, and 3) computer polluta nt removal by selected BMPs. Two 8 spreadsheets have been developed, one for new devel opment and one for redevelopment projects 9 that allow the designer to see whether the phosphor us load reduction has been achieved by the 10 application of runoff reduction practices. www.dcr.virginia.gov/lr2f.shtml 11



### LID Quicksheet 1.2 12 Developed by the Milwaukee Metropolitan Sewerage Di strict (MMSD), LID Quicksheet 1.2 is a 13 calculation spreadsheet that has been developed to provide a practical way to calculate how the 14 use of particular low impact development practices affect the stormwater detention volume 15 required under Chapter 13. The LID practices includ ed in the Quicksheet are rain gardens, rain 16 barrels, green roofs, cisterns, and permeable pavem ent. The intent of the Quicksheet is to allow 17 the designer to evaluate the effect of LID practice s on reducing the volume of traditional 18 stormwater detention. Information on LID Quicksheet 1.2 is available in Appendix L at: 19 http://v3.mmsd.com/manuals.aspx

. 20 

### Emeryville Stormwater Sizing Calculator 21 The City of Emeryville, California developed this s preadsheet-based calculator to determine the 22 proper size of stormwater treatment devices for new development projects. The spreadsheet 23 includes 7 tables each targeted to a specific type of stormwater treatment information. The tool 24 uses user-defined drainage area and types to calcul ate the required facility size for the area. It 25 also calculates the amount of shortfall in metered detention areas, bioretention basins, lowered 26 planter strips, flow-through planter boxes, and bio retention swales. The tool can help track 27 treatment capacity excess and shortages so that par cel areas can be redistributed if there is a 28 shortfall. This tool along with others can be acces sed at 29 http://cfpub.epa.gov/npdes/greeninfrastructure/mode lsandcalculators.cfm

. 30 

### Capitol Region Watershed District (Twin Cities, Minnesota MN ), Volume 31 

### Reduction Worksheet 32

: This spreadsheet includes formulas for volume reduc tion practices. Volume credits are 33 provided for seven different types of practices. www.capitolregionwd.org/permit_forms.html 343/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 224 

### The Center for Neighborhood Technology Green Values Calculator (GVC) 1 The GVC compares green infrastructure performance, costs, and benefits to conventional 2 stormwater practices at both development-site and n eighborhood scales. The tool provides a 3 quantified analysis of green infrastructure environ mental benefits including reduced runoff 4 volume and groundwater recharge. Users can specify site data in a custom run or use several 5 templates for typical urban and suburban scenarios. A number of “green interventions” can be 6 selected and used to calculate financial and hydrol ogic reduction data. Hydrologic reductions 7 include lot-level goals for peak and total discharg e, desired total site peak discharge, total 8 detention required, and average annual discharge. T he GVC is maintained by The Center for 9 Neighborhood Technology and can be accessed at http://greenvalues.cnt.org

. 10



### SELECT 11 The System Effectiveness and Life-cycle Evaluation of Costs Tool (SELECT) is a simple 12 planning-level tool that enables a stormwater manag er to examine the effectiveness of alternative 13 scenarios for controlling stormwater pollution and the whole-life cost associated with each 14 scenario. SELECT uses a long-term record of hourly rainfall which it translates into runoff using 15 a runoff coefficient that is related to the effecti ve imperviousness of the catchment. This runoff is 16 introduced to the BMP (which include a number of co mmon BMPs, including permeable 17 pavement, wetlands, and swales). If there is capaci ty in the BMP, the runoff is captured; if the 18 BMP is full, the runoff is discharged untreated to the receiving waters. The model calculates total 19 outflow as the sum of what is treated and what is n ot. 20 This tool was developed for the Water Environment R esearch Foundation (WERF) by a team 21 including ACR, LLC, the University of Utah, and Col orado State University and uses Microsoft 22 Excel as an interface. SELECT is currently only ava ilable to WERF subscribers. More 23 information, including how to become a WERF subscri ber and download the tool, can be found 24 here www.werf.org/select

. 25


### Upper Neuse Site Evaluation Tool (SET) 26 The Upper Neuse Site Evaluation Tool (SET) is a spr eadsheet-based tool developed by Tetra 27 Tech, Inc. for the Upper Neuse River Basin Associat ion. It was designed to aid in the assessment 28 of development plans and available BMPs to achieve regional water quality objectives. The SET 29 can also be used to compare the costs of stormwater BMP systems and estimate the cost savings 30 for reducing impervious surfaces within a site desi gn. The most recent version of the SET can be 31 found at www.unrba.org/set

. 32 The SET has two functioning components – the Hydrol ogy/Pollutant Component for assessing 33 water quality impacts of development, and the Cost Component for assessing the costs of BMPs 34 and other infrastructure. The Hydrology/Pollutant C omponent requires user-controlled targets for 35 nutrient loading, an optional target for sediment l oading, and targets for peak flow for storage of 36 runoff during the type of storm events most likely to cause downstream channel erosion. Data 37 entry includes general site data, land use, drainag e areas and BMP information. Various BMPs 38 can be tested to find a combination that meets the targets. The Cost Component allows a user to 393/15/20 2

- 22

- 10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote —

Chapter 3. Controlling Urban Runoff 225 compare the costs of stormwater BMP systems and est imate the cost savings for reducing 1 impervious surfaces within a site design 2


### Rainwater Harvester Computer Model 3 North Carolina State University developed a compute r model to assist in determining the 4 appropriate cistern size for a given situation. The model uses rainfall data and anticipated usage 5 to establish cistern inputs and outputs and provide s a cost summary and usage statistics in a 6 report form. Version 2.0 includes an improved inter face, reduced calculation times, an interactive 7 graph of cistern levels, and the ability to save an d load model inputs. Also, the website also 8 includes a quick online calculator that provides an overview of the benefits of a water harvesting 9 system for homeowners. www.bae.ncsu.edu/topic/waterharvesting/model.html 10