National Park Service

U.S. Department of the Interior

Natural Resource Program Center

WATER RESOURCES INFORMATION AND 

ISSUES OVERVIEW REPORT

BENT’S OLD FORT NATIONAL HISTORIC SITE

Natural Resource Report NPS/NRPC/WRD/NRR—2010/258

 

 

 

 

 

 

 
ON THE COVER

Photographic credits, clockwise from upper left: legendsofamerica.com

 everywhereorg.com

 flickr.com

 legendsofamerica.com

 sangres.com/colorado/national_parks
WATER RESOURCES INFORMATION AND 

ISSUES OVERVIEW REPORT

BENT’S OLD FORT NATIONAL HISTORIC SITE

Natural Resource Report NPS/NRPC/WRD/NRR—2010/258

David L. Vana-Miller 

Water Resources Division

Natural Resource Program Center

P.O. Box 25287

Denver, CO 80225

Courtney Moore

Bent’s Old Fort National Historic Site

35110 Highway 194 East

La Junta, CO 81050

Jeff Hughes

Water Resources Division

Natural Resource Program Center

1201 Oak Ridge Dr., Suite 250

Fort Collins, CO 80525

Kevin F. Noon

Water Resources Division

Natural Resource Program Center

P.O. Box 25287

Denver, CO 80225

October 2010

U.S. Department of the Interior

National Park Service

Natural Resource Program Center

Fort Collins, Colorado
ii

The National Park Service, Natural Resource Program Center publishes a range of reports that 

address natural resource topics of interest and applicability to a broad audience in the National 

Park Service and others in natural resource management, including scientists, conservation and 

environmental constituencies, and the public.

The Natural Resource Report Series is used to disseminate high-priority, current natural resource 

management information with managerial application. The series targets a general, diverse 

audience, and many contain NPS policy considerations or address sensitive issues of 

management applicability.

All manuscripts in the series receive the appropriate level of peer review to ensure that the 

information is scientifically credible, technically accurate, appropriately written for the intended 

audience, and designed and published in a professional manner. This report received informal 

peer review by subject-matter experts who were not directly involved in the collection, analysis, 

or reporting of the data.

Views, statements, findings, conclusions, recommendations, and data in this report do not 

necessarily reflect views and policies of the National Park Service, U.S. Department of the 

Interior. Mention of trade names or commercial products does not constitute endorsement or 

recommendation for use by the U.S. Government.

This report is available from the Natural Resource Publications Management website 

(http://www.nature.nps.gov/publications/NRPM ).

Please cite this publication as:

Vana-Miller, D., C. Moore, J. Hughes and K. Noon. 2010. Water resources information and 

issues overview report: Bent’s Old Fort National Historic Site. Natural Resource Report 

NPS/NRPC/WRD/NRR—2010/258. National Park Service, Fort Collins, Colorado.

NPS 417/105853, October 2010
iii

Contents

Page

Figures............................................................................................ 

Tables............................................................................................. 

Executive Summary............................................................................

Acknowledgments..............................................................................

 v

 vii

 ix

xiv

Introduction...................................................................................... 

Park Location and Description.......................................................

Importance of Planning to Water Resources Management.......................

Legislation, Management, and Coordination of Water Resources

at Bent’s Old Fort National Historic Site...........................................

Federal Laws..................................................................

State of Colorado Laws and Regulations..................................

National Park Service Policies and Director’s Orders...................

Management Agencies.......................................................

Stakeholders at Local Level.................................................

Related Management Plans and Programs.................................

Description of Resources......................................................................

Climate..................................................................................

Land Use................................................................................

Physiography, Geology, Soils, and Vegetation.....................................

River Geomorphology.................................................................

Hydrogeology..........................................................................

Ground Water Quality........................................................

Surface Water Hydrology............................................................

Surface Water Quality........................................................

 1

 1

 3

 4

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 8

 9

 12

 14

 15

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 17

 17

 19

 24

 27

 28

 29

 35
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Floodplains, Wetlands, and Riparian Areas........................................

Aquatic Biological Resources........................................................

Water-based Birds............................................................

Water-based Mammals......................................................

Fish.............................................................................

Amphibians and Reptiles....................................................

Drinking Water........................................................................

Water Resource Issues and Recommendations.............................................

Water Rights and Ground Water Wells.............................................

Water Quality and Quantity of the Arkansas River...............................

High Water Table and Impacts to Bent’s Old Fort...............................

Wetland and Riparian Protection....................................................

Flooding and Stormwater Drainage.................................................

Sewage Treatment and Septic Systems.............................................

Hazardous Waste Management and Spill Contingency Planning...............

Water Resources of Bent’s Old Fort National Historic Site and 

Climate Change.................................................................................

Literature Cited.................................................................................

 42

 47

 47

 48

 48

 48

 50

 53

 53

 57

 59

 61

 63

 65

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 69
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Figures

 Page

Figure 1. Map of Bent’s Old Fort NHS and the surrounding area........................ 2

Figure 2. The NPS framework for planning and decision making...................... 4

Figure 3. Average annual visitation in thousands for Bent’s 

 Old Fort National Historic Site, 1964-2006.................................... 18

Figure 4. Aerial photograph (left; circa 1993) and topographic

 map (right; circa 1953) of Bent’s Old Fort National 

 Historic Site and surrounding area............................................... 20

Figure 5. Surficial geology of Bent’s Old Fort National Historic Site.................. 21

Figure 6. Soils of Bent’s Old Fort NHS.................................................... 22

Figure 7. Vegetation map for Bent’s Old Fort NHS...................................... 23

Figure 8. Hypothesized metamorphosis in the Arkansas River at Bent’s

 Old Fort National Historic Site................................................... 26

Figure 9. Mean and spatial variation of specific conductance in the 

 lower Arkansas River alluvial ground water.................................... 29

Figure 10. Locations of Cretaceous marine shale in the Arkansas 

 River Basin of Colorado........................................................... 30

Figure 11. The Arkansas River basin in Colorado......................................... 31

Figure 12. Upper Arkansas Lake Meredith watershed (HUC 11020005) 

 in the Arkansas River basin of southeastern Colorado........................ 32

Figure 13. Representative hydrographs for the Arkansas River at

 La Junta, CO (USGS gaging station 07123000)............................... 33

Figure 14. Mean daily discharge from 1912-2007 for the Arkansas 

 River at La Junta, CO............................................................... 34 

Figure 15. Map of Lower Arkansas River from Rocky Ford to John 

 Martin Reservoir showing location of the Fort Lyon Canal 

 in relation to the river and Bent’s Old Fort NHS............................... 34
vi

Figure 16. Total annual discharge of the Arkansas River at La Junta 

 and Fort Lyon Canal, 1917-1994, showing the disparity

 in flow between the two systems.................................................. 35

Figure 17. Mean annual flow from 1975-2006 for the Las Animas, 

 CO gage site (USGS 07124000) on the Arkansas River....................... 36

Figure 18. Sulfate concentrations along the lower Arkansas River

 in Colorado........................................................................... 39

Figure 19. Selenium concentration in the Lower Arkansas River

 (upstream to downstream) and major tributaries............................... . 39 

Figure 20. Specific conductance in the lower Arkansas River 

 and major tributaries................................................................ 40

Figure 21. Seasonal relationship of stream flow to specific conductance 

 for the Arkansas River near Avondale........................................... 41

Figure 22. Plot from the National Weather Service’s Advanced 

 Hydrologic Prediction Service of actual and forecasted

 stage height and flow for the June 5-15, 2010 period for 

 the La Junta gage.................................................................... 43 

Figure 23. Plot from the National Weather Service’s Advanced 

 Hydrologic Prediction Service of river stage versus

 exceedance probability for the May 27-September 23, 

 2010 time period for the La Junta gage........................................... 44

Figure 24. Locations of wetlands in Bent’s Old Fort NHS................................. 45

Figure 25. Locations of ground water monitoring wells and Arkansas 

 River staff gages from the study by Woods et al. (2002)....................... 60

Figure 26. View of the park employee entrance gate as it passes along the 

 maintenance and administration buildings....................................... 64
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Tables

 Page

 

Table 1. Monthly clmate summary for the La Junta, CO station

 (#054726) from 1982-2005............................................................. 17

Table 2. Changes in fluvial geomorphologic features of the 

 Arkansas River at Bent’s Old Fort NHS, 1870-1977.............................. 

Table 3. Fish species collected at Bent’s Old Fort NHS by 

 three studies............................................................................

 25

 49
viii
ix

Executive Summary

This Water Resources Information and Issues Overview Report is one of several planning 

products offered by the National Park Service Water Resources Division that assists national 

park units with achieving or maintaining water resource integrity.

Bent’s Old Fort National Historic Site (NHS) is a 799.8-acre national park unit in Otero County 

of southeastern Colorado, approximately 7.5 miles northeast of the town of La Junta. The park 

was authorized in 1960 for the purpose of establishing a national historic site at the location of 

Bent’s Old Fort on the Santa Fe Trail. The NHS commemorates the Bent-St. Vrain Trading 

Empire, which radiated from Bent’s Old Fort into what are now Texas, New Mexico, Kansas, 

Nebraska, Arizona, Utah, Wyoming and Missouri. Bent’s Old Fort was an important point of 

commercial, social, military, and cultural contact between Anglo-American, Native Tribes, 

Hispanic, and various minority cultures on the border of the U. S. Territory. The original adobe 

fort was constructed in 1833 on the edge of a low, floodplain terrace, approximately 300 yards 

from the Arkansas River. This location served the strategic purpose of furthering trade along the 

Santa Fe Trail. 

This Water Resources Information and Issues Overview Report was developed at the request of 

the NHS. It represents an important collation and summarization of water resource information; 

an identification of applicable federal, state and local legislation and policy that affect the 

management water resources; an assessment of current water resource status; and, an 

identification and analysis of water resource issues that the NHS is currently facing, and 

recommends future management actions or directions to address those issues.

The report is organized into four major sections. The first, Introduction, describes the NHS, 

outlines the laws, regulations, and policies relevant to water resource management at the NHS, 

and describes the varying roles of federal, state, regional, and local agencies in water resources 

management along the Arkansas River. 

The second section, Description of Resources, describes the NHS and its surrounding area in 

terms of climate, physiography, geology/soils, land use, surface and ground water hydrology and 

quality, wetlands and riparian areas, and aquatic biological resources. It also describes the 

geomorphology of the Arkansas River.

The third section, Water Resource Issues and Recommendations, describes the water resource 

issues identified by NHS staff during an internal scoping process. In addition, this section

provides recommendations for future action or direction that NHS management may consider. 

Water resource issues and recommendations are as follows:

• Water Rights and Ground Water Wells

Water rights information should be updated to fill in missing information as to the history 

and present status of NHS water rights for both the park files and NPS Water Rights 

Branch dockets. In order to accomplish this task, files from the Colorado Division of 
x

Water Resources, Fort Lyon Canal Company, and the Colorado Water Court should be 

reviewed and copies made of missing information for each well and ditch right. 

Submitting a Technical Assistance request to the NPS, Water Resources Division is an 

option if the NHS does not have the staff or expertise in this matter. Also, an analysis 

should be made by the NHS as to its current and future water needs to determine if 

existing NHS water rights are adequate. If certain wells and/or water rights are no longer 

needed, an effort to properly abandon the well(s) and right(s) should be undertaken. 

Since more irrigation use is planned for other areas of the NHS, an effort should be made 

to see if the NHS shares in the Fort Lyons Canal Company could be exchanged for the 

right to divert tributary ground water from the Arkansas River basin.

• Water Quality and Quantity of the Arkansas River

An effort by the NPS in 1998 provided a basic retrospective analysis of water quality 

conditions at those monitoring stations with records in STORET, the national water 

quality database. In our estimation that analysis was and is of limited value to the NHS, 

simply because the closest upstream station with an adequate period of record is in La 

Junta, 8 miles west of the NHS. The closest downstream station is on the Arkansas River 

at Hadley, CO (USGS #07123300 and BEOL 7), two miles downstream. However, that 

station has been inactive since the 1980’s and has a very limited period of record that did 

not measure discharge. The La Junta station (USGS #07123000) has an adequate period

of record (in some cases > 50 years and current) for most of the five core water quality 

vital signs. Additionally, other important constituents (e.g. calcium, sulfate, selenium) 

also have adequate periods of record. Most importantly, discharge is measured at this 

station. Because there are no permanent water inputs to the Arkansas River between La 

Junta and the NHS, the analysis of water quality data from the La Junta station would 

provide useful information. We recommend that the NHS submit a technical assistance 

request to the NPS Water Resources Division for a status and trends analysis of water 

quality and discharge information for the La Junta station. 

We recommend two options for the establishment of routine water quality monitoring of 

the Arkansas River at the NHS. First, the Southern Plains Inventory and Monitoring 

Network (SOPN) could establish a core vital signs monitoring site just downstream of the 

west boundary of the NHS; a quarterly sampling frequency would be the minimum. 

These water quality data could be correlated with the discharge data of the La Junta 

station. Additionally, the network could data mine the La Junta site for other important 

constituents. Second, the network or NHS could totally rely on the mining of discharge 

and water quality data from the La Junta station.

Routine monitoring of biological condition is an important tool in understanding overall 

water resource condition. Because the sampling, identification, and analysis of the 

aquatic macroinvertebrate community require specialized expertise, we do not 

recommend this as something to be accomplished by the NHS. The SOPN would be the 

NPS entity better suited for the lead in such an assessment; however, understanding 

aquatic biological condition is not a SOPN vital sign, and may be of low priority.
xi

Colorado’s Ecological Monitoring and Assessment Program (EMAP) within the 

Colorado Department of Public Health and the Environment developed bioassessment 

tools for use in monitoring and assessing streams statewide. We recommend that the 

NHS contact the Colorado Department of Public Health and the Environment and 

propose that the State sample the Arkansas River macroinvertebrate community within 

the boundaries of the NHS as an additional stressed site. This would be a limited 

assessment to assist the State with refining its macroinvertebrate assessment tool of the 

Colorado plains. For the long-term, perhaps the NHS and State could develop a 

Memorandum of Agreement for the State to monitor the macroinvertebrate community of 

the Arkansas River at the NHS on a recurring basis as part of a statewide assessment of 

stream biological condition. 

• High Water Table and Impacts to Bent’s Old Fort

Given that ground water quantity is a vital sign of the SOPN, we agree with the 

recommendations by outlined by a Texas State University study in 2007 for the SOPN, namely:

• Historic and future ground water elevation data should be consolidated within an 

electronic database and coordinated with the operation of an appropriate national or 

state-related database, and

• Given the connection between periodically high water tables and flooding of the Fort, the 

NHS should renovate at least a select few of the PVC-lined, hand augured and well-point 

driven piezometers installed in 2002 for a previous study and renew efforts to monitor 

ground water elevations.

With regard to the first recommendation, we suggest that the NHS submit a technical assistance 

request to the NPS Water Resources Division for assistance with the database and any 

integration with national/state databases.

With regard to the second recommendation, we suggest the renovation of five wells that 

represent either a close association with the Fort and lack of correlation with river stage or a 

strong correlation with river stage due to floodplain locations. Water table elevations in these 

wells should be monitored monthly and linked with monthly-monitored levels at two Arkansas 

River staff gages and other appropriate benchmarks. This will link river stage levels with 

hydraulic head. 

For the present, we do not agree with a 2002 recommendation that a more detailed term study of 

different water sources and aquifer properties is needed to parse out of the relative effects of 

river, canal and excess irrigation on water table levels and basement flooding at the Fort. Such 

knowledge, while of heuristic value, would do little in terms of improving knowledge and 

mitigating the flooding problem. That basement flooding of the Fort is caused by a combination 

of high river stage and canal seepage/excess irrigation is of high scientific probability based on a 

previous study. Therefore, barring the improbable -- moving the location of the Fort, the NHS 

should center its energy on mitigation and remediation of the Fort basement, although the 

available methods are limited. In addition, the NHS should work with such local entities as the 
xii

Southeast Colorado Resource Conservation and Development Council to understand and 

mitigate the amount of excess irrigation and canal leakage flowing towards the NHS. 

• Wetland and Riparian Protection

We concur with a previous recommendation to periodically monitor the aquatic plants and 

animals and recommend a recurrence interval of every five years. Additionally, we recommend 

monitoring for a suite of water quality parameters in the NHS wetlands and would specifically 

include pH, temperature, dissolved oxygen, specific conductance, nitrogen (dissolved ammonia, 

total ammonia + organic, dissolved nitrate and nitrite, and dissolved nitrite), and phosphorus 

(dissolved and ortho-phosphorus dissolved). Sampling locations should be fixed; in the case of 

the Arch and Casebolt wetlands, sampling should occur at the previous well monitoring sites for 

those wetlands. Sampling frequency, initially, should be quarterly, and depending upon the 

analysis of data for a three to five year timeframe, sampling could occur annually (summer). 

Additionally, we recommend the establishment of a monitoring station on the Arch Wetland that 

is down gradient from the septic system at the Fort – this site should be monitored at least 

quarterly for nitrogen and phosphorus constituents.

We agree with a previous recommendation to renovate the monitoring wells established in 2002 

in the Arch and Casebolt wetlands. Ground water elevations should be recorded on a monthly 

basis and linked with levels at Arkansas River staff gages, other ground water monitoring wells, 

and other appropriate benchmarks so that that all sites can be associated with hydraulic head and 

stream stage.

We recommend that the artificial wetlands (Day Pond, Day Wetland, and stock tank wetlands) be 

managed for their wetland functions, which include floodwater storage/attenuation, ground water 

recharge, amphibian breeding habitat, and other wildlife habitat.

It is recommended that the NHS submit a technical assistance request to the NPS Water 

Resources Division for an assessment of the riparian conditions along the Arkansas River using 

The Process for Assessing Proper Functioning Condition. We recommend that the recurrence 

interval for additional assessments be every five years.

Additionally, the NHS should establish GPS-based photograph points on the banks of the 

Arkansas River. Photographic monitoring is a simple and inexpensive method to assess changes 

in stream geomorphology, the riparian zone, and other physical habitat features that may be 

associated with site and watershed conditions. A series of photographs would also allow 

detection of slow, progressive changes in physical habitat features that otherwise might go 

undetected until the accumulation of impacts is noticeable. 

• Flooding and Stormwater Drainage

Storm drainage around the NHS employee entrance road to the maintenance yard and 

administration building is a problem during most heavy rain events. A drainage ditch runs along 

the west side of the road. One possible solution to the drainage problem is to design an outfall at 

the south end of the ditch. A ditch and/or culvert extension should be placed to allow positive 
xiii

drainage from the south end of the existing ditch to an area that is lower in elevation. It appears 

from field observations that one option would be to run a culvert to the southeast under the entry 

road that would day light at a lower elevation in the open field. Since the area seems relatively 

flat, the culvert may have to be quite long in order to meet grade at a lower elevation in the field. 

The low areas in the field have water lines and sewer pump station pipes that may or may not 

allow deposition of sheet flow from the ditch. Another option is to continue the ditch and 

culverts to the south along the entry road. However, this would end up contributing to the 

existing drainage system that is further south, which serves the parking lot for the visitor center, 

and the additional flow may overload that system. The following tasks need to be completed in 

order to identify, select, and implement the best solution:

o Complete a detailed topographic survey (no more than one-foot contour elevations) of the 

entire drainage ditch including culvert inverts, and the survey should also include the area 

at least 100 feet on either side of the existing ditch, the area around the southern end of 

the ditch including the road south to the visitor center parking lot, and the open field area 

(for several hundred feet east of the entry road). 

o Analyze the topography to determine the best solution. Consider the length of culvert 

necessary depending on the amount of drop in elevation needed to move the water, 

clogging and maintenance problems, potential erosion problems, and impacts to other 

infrastructure. Also consider other options including detention basin(s).

o Replace all of the culverts in, and dredge, the existing ditch. Since the culvert is acting 

like a detention basin, the sediment laden water collects in the ditch, slows down, and 

deposits sediment such that the culverts are half-buried and the ditch is filling with silt. 

• Sewage Treatment and Septic Systems

We recommend the monitoring of nitrogen and phosphorus as part of a monitoring program for 

the Arch Wetland.

• Hazardous Waste Management and Spill Contingency Planning

The NHS should strongly consider developing an Oil Spill Prevention and Response Plan. Such 

a plan would present site-specific information on those locations in the NHS that have the 

potential to experience such environmental change. In addition, general structural and 

operational recommendations would be outlined to prevent spills associated with all on-site 

activities involving the storage and/or use of petroleum products or other hazardous materials. A 

notification sequence, including emergency contacts, would be provided if a spill occurs. The 

Plan would be intended for use by all personnel responsible for storage, handling, and removal of 

hazardous substances at the NHS.

The fourth and final section, Water Resources of Bent’s Old Fort National Historic Site and 

Climate Change, briefly describes the possible future water resource conditions under projected 

climate scenarios.
xiv

Acknowledgments

We would like to express our sincere appreciation to Alexa Roberts and Fran Pannebaker, 

Superintendent and Chief of Natural Resources for Bent’s Old Fort National Historic Site, 

respectively, for their support during the development of this document and their perseverance in 

dealing with the numerous delays in publication of this report. We also thank the staff of the 

Maintenance Division for providing information on water-based infrastructure at the NHS. We 

thank the following individuals who reviewed the report and provided helpful comments: Fran 

Pannebaker; Robert Bennetts; John Reber; Mark Flora; Mike Martin; and Don Weeks.
1

Introduction

Park Location and Description

Bent’s Old Fort National Historic Site (NHS) is a 799.8-acre national park unit in Otero County 

of southeastern Colorado, approximately 7.5 miles northeast of the town of La Junta (Figure 1). 

It is bordered on the north by State Highway 194 and on the south by U.S. Highway 50. 

Approximately 2.28 river miles of the Arkansas River flow within the boundary of the NHS. 

In 1960, PL 86-487 authorized the park unit for the purpose of establishing a national historic 

site at the location of Bent’s Old Fort on the Santa Fe Trail. The original site contained 178 

acres; approximately 622 acres were added to the NHS by PL 95-625 in 1978. The Santa Fe 

Trail was designated a National Historic Trail by PL 100-35 in 1987.

The historic site commemorates the Bent-St. Vrain Trading Empire, which radiated from Bent’s 

Old Fort into what are now Texas, New Mexico, Kansas, Nebraska, Arizona, Utah, Wyoming 

and Missouri. Bent’s Old Fort was an important point of commercial, social, military, and 

cultural contact between Anglo-American, Native Tribes, Hispanic, and various minority 

cultures on the border of the U. S. Territory (NPS 1994).

The original adobe fort was constructed in 1833 on the edge of a low floodplain, terrace, 

approximately 300 yards from the Arkansas River. It served as a trade center on the Santa Fe 

Trail. For much of the original fort’s history it was the only major permanent white settlement on 

the Trail. In addition to supplying goods to the pioneers and the military, the fort became a 

staging area for the U.S. Army during the Mexican War in 1846. The fort was abandoned in 

1849.

Gardner (2004) described the Arkansas River as a directional beacon and landmark for overland 

travelers. The Arkansas River was, at the time of the original fort, the border between the U.S. 

and New Mexico. The fort’s location along the Arkansas River was a strategic position to further 

the main purpose of the Fort -- trade along the Santa Fe Trail. Vital natural resources were 

provided by the Arkansas River. 

According to historical accounts, the Arkansas River near the fort was a large, meandering river 

with semi-turbid water, a gravel bottom, a rapid current of 4-6 miles/hr, and sparsely populated 

with cottonwoods and diverse types of life (Swenson 1970). The river was shallow enough in 

places to be forded, accessing trade routes to the south -- an important crossing could possibly 

have been located just east of the fort. 

Droughts spurred the change from the dryland farming of the 1880’s to the development of 

diversion and irrigation programs using water from today’s Arkansas River. This new recharge 

to the river, in effect, raised the water table above the river bed in late summer and changed the 

hydrologic character of the river from intermittent to perennial (Nadler and Schumm 1981). 

These irrigation programs and associated water rights have a long history of litigation between 

farmers, canal companies, and states all contending for limited water rights. Some of this 

conflict was mitigated by the construction of John Martin and Pueblo dams, downstream and 

upstream of the NHS, respectively, which serve as storage for winter runoff and flood waters, 
2

Figure 1. Map of Bent’s Old Fort NHS and surrounding area (from NPS 1998).
3

and regulate the flow of the river. Drought and water rights continue to be challenges. 

Presently, there is pressure to divert water to growing urban areas along the Front Range.

Importance of Planning to Water Resources Management

Water is a particularly important and sensitive ecosystem component, and it plays a central role 

in the social, economic, environmental, and political mosaic of our national park units. Its 

physical availability and quality are critical determinants of a park’s overall natural resource 

condition. Because of the important role of water in maintaining resource condition, it is the 

policy of the NPS to maintain, rehabilitate, and perpetuate the inherent natural integrity of water 

resources and water-dependent environments occurring within national park system units.

Proper management of water resources within the NPS is becoming more complex and 

challenging as threats to these resources, both internal and external to park boundaries, increase. 

Scientists and managers are increasingly called upon to respond to disruptions of water resources 

that threaten the quality of human life and environmental sustainability. Planning is an essential 

first step in addressing these threats and disruptions. The Planning Program of the Water 

Resources Division (WRD) of the NPS has assisted in the development of park-wide 

management strategies and ensured that park managers and policy makers have adequate and 

timely information to protect, utilize and enhance water resources. Several recurrent themes have 

emerged from the water resources planning process:

• Effective management solutions to water resource issues will be achieved only with the 

understanding that changes in environmental conditions are directly linked to 

socioeconomic patterns and processes, especially land use.

• Interactive partnerships among scientists, policy makers, and resource managers are 

essential for developing a comprehensive approach to integrating water sciences with 

management of water resources.

• Viewing water problems holistically and integrating research and management into a 

watershed context links the sciences involved in water research and management.

• The transfer of scientific information to regional/local leaders and the public should be 

done in a manner that will produce an informed and responsive citizenry, and

• Proposed recommendations are connected to issues that are related directly to societal 

needs, such as restoring and rehabilitating ecosystems, maintaining biodiversity, and 

understanding the effects of modified hydrologic flow.

• Climate change is an overarching challenge with potentially grim consequences to water 

resources managements.

Changes in NPS park planning standards (2004 Park Planning Program Standards) have reframed park planning through six discrete elements of planning; the water planning process and 

its products are designed to integrate into this framework (Figure 2). Outside of this framework, 

the Water Resources Information and Issues Overview Report (not shown in Figure 2) is 

designed as a flexible document that addresses a park’s specific needs with regard to water 

resources that are outside of the park planning framework. However, its contents may be used to 

support park planning efforts, particularly the General Management Plans and/or Program 

Management Plans. For the NHS, this Water Resources Information and Issues Overview

Report is an important collation and summarization of water resource information, an 
4

identification of applicable federal, state, and local legislation and policy that affect the 

management of water resources, an assessment of current water resource status, an identification 

and analysis of water resource issues, and an assessment of future actions or management 

directions. 

Foundation

GMP

Program

Mgmt 

Plans Strategic

Plan Implementation

Plans

Annual Performance Plan 

and Report

WHY WHAT HOW

PLANNING FRAMEWORK

LONG TERM SHORT TERM

Water Resources 

Foundation Report

Water Resources 

Stewardship Report

Figure 2. The NPS framework for planning and decision making (green boxes). Red-outlined boxes 

represent WRD planning documents. RSS = Resource Stewardship Strategy; GMP = General 

Management Plan.

Legislation, Management, and Coordination of Water Resources in Bent’s Old 

Fort National Historic Site

Many federal, state, and local agencies have an interest, mandated or otherwise, in the water 

resources at the NHS. Protection of water resources requires an understanding of the various 

policy, regulatory, and management designations in order to facilitate coordination and 

cooperation among agencies and private landowners at the NHS. Both federal and state agencies 

have authority for the enforcement of appropriate regulations. Water resource laws and 

regulations at the state and local levels are often patterned after federal laws, or serve in response 

to federal directives. 

Federal Laws and Regulations

National Park Service Organic Act of 1916: This act created the NPS and includes a significant 

management provision stating that the NPS shall promote and regulate the use of the federal 

areas known as national parks, monuments, and reservations by such means and measures as 

conform to the fundamental purpose of the said parks, monuments, and reservations, which 
5

purpose is to conserve the scenery and the natural and historic objects and the wild life therein 

and to provide for the enjoyment of the same in such manner and by such means as will leave 

them unimpaired for future generations. The Organic Act also authorizes the NPS to regulate the 

use of national parks and develop rules, regulations and detailed policies to implement the broad 

policies provided by Congress. Rules and regulations for the national park system are described 

in the Code of Federal Regulations (Title 36). 

General Authorities Act of 1970: This Act reinforced the 1916 Organic Act – all park lands are 

united by a common preservation purpose, regardless of title or designation. Hence, federal law 

protects all water resources in the national park system equally, and it is the fundamental duty of 

the NPS to protect those resources unless otherwise indicated by Congress.

Redwood National Park Act (1978): This Act amended the General Authorities Act of 1970 

identifying the high public value and integrity of the national park system as reason to manage 

and protect all park system units. The act further stated that no activities should be allowed that 

will compromise the values and purposes for which these various areas have been established, 

except where specifically authorized by law or provided for by Congress.

National Parks Omnibus Management Act of 1998: This Act attempts to improve the ability of 

the NPS to provide state-of-the-art management, protection, and interpretation of and research on 

the resources of the national park system by: 

• Assuring that management of units of the national park system is enhanced by the 

availability and utilization of a broad program of the highest quality science and 

information;

• Authorizing the establishment of cooperative agreements with colleges and universities, 

including but not limited to land grant schools, in partnership with other federal and state 

agencies, to establish cooperative study units to conduct multi-disciplinary research and 

develop integrated information products on the resources of the national park system, or 

of the larger region of which parks are a part;

• Undertaking a program of inventory and monitoring of national park system resources to 

establish baseline information and to provide information on the long-term trends in the 

condition of national park system resources; and

• Taking such measures as are necessary to assure the full and proper utilization of the 

results of scientific study for park management decisions. In each case in which an 

action undertaken by the NPS may cause a significant adverse effect on a park resource, 

the administrative record shall reflect the manner in which unit resource studies have 

been considered. The trend in the condition of resources of the national park system shall 

be a significant factor in the annual performance.

National Environmental Policy Act (NEPA) of 1969: This Act requires federal agencies to 

evaluate the environmental impacts of their actions and to integrate such evaluations into their 

decision-making processes. NEPA’s basic policy is to assure that all branches of government 
6

give proper consideration to the environment prior to undertaking any major federal action that 

significantly affects the environment.

Clean Water Act of 1972 (Federal Water Pollution Control Act): The Federal Water Pollution 

Control Act, more commonly known as the Clean Water Act, was first promulgated in 1972 and 

amended several times since (e.g., 1977, 1987, and 1990). This law is designed to restore and 

maintain the chemical, physical and biological integrity of the nation’s waters, including the 

waters of the national park system. To achieve this, the act called for a major grant program to 

assist in the construction of municipal sewage treatment facilities, and a program of effluent 

limitations designed to limit the amount of pollutants that could be discharged. Effluent 

limitations are the basis for permits issued for all point source discharges, known as the National 

Pollutant Discharge Elimination System (NPDES).

As part of the act, Congress recognized the primary role of the states in managing and regulating 

the nation’s water quality. Section 313 requires that all federal agencies comply with the 

requirements of state law for water quality management, regardless of other jurisdictional status 

or landownership. States implement the protection of water quality under the authority granted 

by the Clean Water Act through best management practices and through water quality standards. 

Standards are based on the designated uses of a water body or segment of water, the water 

quality criteria necessary to protect that use or uses, and an anti-degradation provision to protect 

the existing water quality. 

Section 303 of the Clean Water Act requires the promulgation of water quality standards by the 

states. Additionally, each state is required to review its water quality standards at least once 

every three years. This section also requires the listing of those waters where effluent limitations 

are not stringent enough to implement any water quality standard [so called 303(d) list]. Each 

state must establish Total Maximum Daily Loads (TMDLs) for applicable pollutants for each of 

the waters on its 303 (d) list.

Section 404 of the Clean Water Act requires that a permit be issued for discharge of dredged or 

fill materials in waters of the U.S., including wetlands. The U.S. Army Corps of Engineers 

administers the Section 404 permit program with oversight and veto powers held by the U.S. 

Environmental Protection Agency. Under Section 401, the State must certify that any 404 action 

meets current state water quality standards.

The 1987 amendment to the Clean Water Act established a stringent nonpoint source control 

mandate. Subsequent amendments further developed this mandate by requiring that states 

develop regulatory controls over nonpoint sources of pollution and over storm water runoff from 

industrial, municipal, and construction activities. 

Endangered Species Act of 1973: This 1973 Act requires the NPS to identify and promote the 

conservation of all federally listed endangered, threatened, or candidate species within any park 

unit boundary. This Act requires all entities using federal funding to consult with the Secretary of 

Interior on activities that potentially impact endangered flora and fauna. It also requires agencies 

to protect endangered and threatened species, as well as designated critical habitats. While not 
7

required by legislation, it is NPS policy to also identify state and locally listed species of concern 

and support the preservation and restoration of those species and their habitats.

Safe Drinking Water Act of 1974: This is the primary federal legislation (1974 with amendments 

in 1986 and 1996) protecting drinking water supplied by public water systems (those serving 

more than 25 people). The act provides for the establishment of primary regulations for the 

protection of the public health and secondary regulations relating to the taste, odor, and 

appearance of drinking water. The law established the current federal-state arrangement in 

which states may be delegated primary implementation and enforcement authority for the 

drinking water program; the 1986 amendments sought to accelerate contaminant regulation. The 

state-administered Public Water Supply Supervision (PWSS) program remains the basic program 

for regulating the Nation’s public water systems.

The 2006 NPS Management Policies cover water supply systems, wastewater systems, and 

recreational waters. Specific guidance is provided by Director’s Order 83: Public Health and its 

associated Reference Manuals – 83A1 (Drinking Water Standards); 83A2 (Cross Connection 

Control); 83A3 (Water System Security); 93B1 (Wastewater Systems); and 83B4 (Sewage Spill 

Response Notification).

Rivers and Harbors Act of 1899: Section 9 of this Act prohibits the construction of any bridge, 

dam, dike or causeway over or in navigable waterways of the U.S. without Congressional 

approval. Administration of section 9 has been delegated to the Coast Guard. Structures 

authorized by state legislatures may be built if the affected navigable waters are totally within 

one state, provided that the plan is approved by the Corps of Engineers and the Secretary of 

Army. 

Under section 10 of the Act, structures of the United States cannot obstruct navigation without 

Congressional authorization. Plans for structures or fill in waters of the United States require 

approval by the Secretary of the Army through the Corps of Engineers. 

Authority of the Corps of Engineers to issue permits for the discharge of refuse matter into or 

affecting navigable waters under section 13 was modified by the Federal Water Pollution Control 

Act Amendments of 1972, as amended, which established National Pollutant Discharge 

Elimination System Permits. 

Fish and Wildlife Coordination Act of 1934: The Fish and Wildlife Coordination Act, as 

amended, provides authority for the U.S. Fish and Wildlife Service to review and comment on 

the effects on fish and wildlife of activities proposed to be undertaken or permitted by the Corps 

of Engineers. 

Amendments enacted in 1946 require consultation with the U.S. Fish and Wildlife Service and 

the fish and wildlife agencies of states where the “waters of any stream or other body of water 

are proposed or authorized, permitted or licensed to be impounded, diverted . . . or otherwise 

controlled or modified” by any agency under a federal permit or license. Consultation is to be 

undertaken for the purpose of “preventing loss of and damage to wildlife resources.”
8

The 1958 amendments added provisions to recognize the vital contribution of wildlife resources 

to the Nation and to require equal consideration and coordination of wildlife conservation with 

other water resources development programs. The amendments also expanded the instances in 

which diversions or modifications to water bodies would require consultation with the U.S. Fish

and Wildlife Service. 

Executive Order 11990: Wetlands Protection: This executive order directs the NPS to 1) provide 

leadership and to take action to minimize the destruction, loss, or degradation of wetlands, 2) 

preserve and enhance the natural and beneficial values of wetlands, and 3) to avoid direct or 

indirect support of new construction in wetlands unless there are no practicable alternative to 

such construction and the proposed action includes all practicable measures to minimize harm to 

wetlands.

Executive Order 11988: Floodplain Management: This executive order requires all federal 

agencies to take action to reduce the risk of flood loss, to restore and preserve the natural and 

beneficial values served by floodplains, and to minimize the impact of floods on human safety, 

health, and welfare. The objective of this executive order is “...to avoid to the extent possible the 

long- and short-term adverse impacts associated with the occupancy and modification of 

floodplains and to avoid direct and indirect support of floodplain development wherever there is 

a practicable alternative.” For non-repetitive actions, the executive order states that all proposed 

facilities must be located outside the limits of the 100-year floodplain. If there were no 

practicable alternative to construction within the floodplain, adverse impacts would be 

minimized during the design of the project.

Executive Order 13112: Invasive Species: This executive order requires the prevention of the 

introduction of invasive species and provides for their control and minimization of the economic, 

ecological, and human health impacts that invasive species cause. It complements and builds 

upon existing federal authority to aid in the prevention and control of invasive species.

State of Colorado Laws and Regulations

Colorado Revised Statutes, Title 25 (Health), Article 8 (Water Quality Control): This Article 

provides for the development and maintenance of water quality standards in Colorado and the 

prevention, abatement, and control of water pollution. Commonly referred to as the Colorado 

Water Quality Control Act, this article is administered by the Water Quality Control 

Commission, the state agency responsible for promulgating rules and regulations to govern water 

quality. Important regulations include:

• Regulation No. 32 – Classifications and Numeric Standards for the Arkansas River Basin 

and Tables;

• Regulation No. 93 – Colorado’s Section 303(d) List of Impaired Waters and Monitoring 

and Evaluation List;

• Regulation No. 41– The Basic Standards for Ground Water

• Regulation No. 42 – Site-Specific Water Quality Classification and Standards for Ground 

Water

• Regulation No. 82 – 401 Certification Regulation
9

• Primary Drinking Water Regulations – 5 CCR 1003-1

Colorado Revised Statutes, Title 33 (Wildlife and Parks and Outdoor Recreation), Articles 1-8 

(Wildlife): These Articles cover the conservation, protection, and enforcement rules for game 

and nongame wildlife. Article 2 covers nongame and endangered species conservation as it 

pertains to the two state-listed nongame fish species that occur in the NHS.

Colorado Revised Statutes, Title 37 (Water and Irrigation), Articles 1-8 (Flood Control), Articles 

60 (Colorado Water Conservation Board), Article 69 (Arkansas River Compact), and Articles 

80-92 (Water Rights and Irrigation): Articles 80-92 are on particular importance to the NHS 

because they cover Colorado water rights law. The doctrine of prior appropriation governs the 

establishment and administration of ground water rights in Colorado. Ground water in Colorado 

is subject to a complex administration scheme. All ground water is presumed by law to be 

tributary to a surface stream; based on that presumption ground water is governed by the prior 

appropriation doctrine and administered in conjunction with surface water rights. Such waters 

are administered through the state's water courts. The state recognizes that not all ground water 

is hydrologically connected to surface streams and provides for administration of such 

nontributary ground waters separately from surface streams, providing different schemes based 

on the degree of hydrologic connection and areal location within the state.

National Park Service Policies and Director’s Orders 

The NPS Management Policies (National Park Service 2006) provide broad policy guidance for 

the management of National Park System units. These NPS policies and guidelines broadly 

require management of natural resources of the National Park System to maintain, rehabilitate, 

and perpetuate the inherent integrity of aquatic resources. Section 4.6 of the management 

policies specifically addresses water resource management including protection of surface waters 

and ground water, water rights, water quality, floodplains, wetlands, and watershed and stream 

processes. It is NPS policy to determine the quality of park surface and ground water resources 

and avoid, whenever feasible, the pollution of park waters by human activities occurring within 

and outside of parks. Specifically, the NPS works with appropriate governmental bodies to: 

achieve the highest possible standards available under the Clean Water Act for protection of park 

waters, take all actions necessary to maintain or restore surface and ground water quality within 

the parks to be in compliance with the Clean Water Act and all applicable laws and regulations, 

and develop agreements with other governing bodies, where appropriate, to obtain their 

cooperation in maintaining or restoring the quality of park water resources. NPS Management 

Policies also direct the NPS to: manage watersheds as complete hydrologic systems, minimize 

human disturbance to natural upland processes that deliver water, sediment, and woody debris to 

streams, and manage streams to protect stream processes that create habitat features, including 

floodplains, riparian systems, woody debris accumulations, terraces, gravel bars, riffles, and 

pools. 

In accordance with these management policies, the NPS will protect watershed and stream 

features mainly by avoiding impacts to watershed and riparian vegetation and allowing natural 

fluvial processes to proceed unimpeded. When conflicts between park infrastructure and stream 

processes are unavoidable, park managers will first consider relocating or redesigning 

infrastructure, instead of manipulating streams. However, where stream manipulation is 
10

inevitable, the NPS will use techniques that protect natural processes to the greatest extent 

practicable. In addition, the NPS will allow natural shoreline processes to continue without 

interference. Where human uses or infrastructure have altered the nature or rate of natural 

shoreline processes, the NPS will investigate alternatives for mitigating such effects. 

Director’s Orders (DO) and Procedural Manuals: National Park Service DO’s and procedural 

manuals describe the recommended procedures for implementing service-wide policy. Those 

DO’s and procedural manuals that pertain most directly to water resources are described below. 

• DO #77-1 and Procedural Manual #77-1: Wetland Protection: The purpose of DO #77-1 

is to establish NPS policies, requirements, and standards for implementing Executive 

Order 11990, Protection of Wetlands (42 FR 26961). The NPS adopts a goal of “no net 

loss of wetlands.” In addition, the NPS will strive to achieve a longer-term goal of net 

gain of wetlands service-wide. DO #77-1 directs NPS units to conduct park-wide 

wetland inventories to help assure proper planning with respect to management and 

protection of wetland resources and sets forth the standard for defining, classifying, and 

inventorying wetlands. For proposed new development or other new activities or 

programs that are either located in or otherwise have the potential for adverse impacts on 

wetlands, the NPS will employ a sequence of: 1) avoiding adverse wetland impacts to the 

extent practicable, 2) minimizing impacts that could not be avoided, and 3) compensating 

for remaining unavoidable adverse wetland impacts via restoration of degraded wetlands. 

Where natural wetland characteristics or functions have been degraded or lost due to 

previous or ongoing human activities, the NPS will, to the extent appropriate and 

practicable, restore them to pre-disturbance conditions. Where appropriate and 

practicable, the NPS will not simply protect, but will seek to enhance natural wetland 

values by using them for educational, recreational, scientific, and similar purposes that do 

not disrupt natural wetland functions. A Wetland Statement of Findings (WSOF) must be 

completed in accordance with procedures described in Procedural Manual #77-1 

(Wetland Protection), when any NPS wetlands are adversely impacted. Procedural 

manual #77-1 provides more detailed procedures by which the NPS will implement DO 

#77-1.

According to the 2006 NPS Management Policies, the NPS will manage wetlands in 

compliance with NPS mandates and the requirements of Executive Order 11990 

(Wetland Protection), the Clean Water Act, and the Rivers and Harbors Appropriation 

Act of 1899, and the procedures described in Director’s Order 77-1. The service will 1) 

provide leadership and take action to prevent the destruction, loss, and degradation of 

wetlands; 2) preserve and enhance the natural and beneficial values of wetlands; and 3) 

avoid direct and indirect support of new construction in wetlands unless there are no

practicable alternatives and the proposed action includes all practicable measures to 

minimize harm to wetlands. The NPS will implement a “no net loss of wetlands” policy.

• DO #77-2 and Procedural Manual #77-2: Floodplain Management: DO #77-2 applies to 

all proposed NPS actions involving floodplain development that could adversely affect 

the natural resources and functions of floodplains or increase flood risks. In compliance 

with Executive Order 11988, Floodplain Management, it is NPS policy to preserve 
11

floodplain values and minimize potentially hazardous conditions associated with 

flooding. Specifically, DO #77-2 directs the NPS to:

o protect and preserve the natural resources and functions of floodplains;

o avoid the long- and short-term environmental effects associated with the 

occupancy and modification of floodplains;

o avoid support of floodplain development and actions that could adversely affect 

the natural resources and functions of floodplains or increase flood risks; and

o restore, when practicable, natural floodplain values previously affected by land 

use activities within floodplains.

When it is not practicable to locate or relocate development or inappropriate human 

activities to a site outside and not affecting the floodplain, NPS will:

o prepare and approve a Floodplain Statement of Findings, in accordance with 

procedures described in Procedural Manual #77-2;

o take all reasonable actions to minimize the impact to natural resources of 

floodplains;

o use non-structural measures as much as practicable to reduce hazards to human 

life and property; and

o ensure that structures and facilities are designed to be consistent with the intent of 

the standards and criteria of the National Flood Insurance Program (44 CFR Part 

60).

Procedural Manual #77-2 establishes NPS procedures for implementing floodplain 

protection and management actions for national park system units in accordance with DO 

#77-2. The manual defines regulatory floodplains and the information required to 

delineate floodplains, defines the information required to evaluate hazards associated 

with the modification or occupation of floodplains, and provides requirements for 

managing activities that impact floodplains.

The 2006 NPS Management Policies state that natural shoreline processes (such as 

erosion, deposition, dune formation, shoreline migration) will be allowed to continue 

without interference. Where human activities have altered the nature or rate of natural 

shoreline processes, the NPS will, in consultation with appropriate state and federal 

agencies, investigate alternatives for mitigating the effects of such activities or structures 

and for restoring natural conditions. New developments will not be placed in areas 

subject to wave erosion or active shoreline processes unless 1) the development is 

required by law; or 2) the development is essential to meet the parks’ purposes, as 

defined by its establishing act of proclamation, and 

o No practicable alternative locations are available,

o The development will be reasonably assured of surviving during its planned life 

 span, without the need for shoreline control measures, and 

o Steps will be taken to minimize safety hazards and harm to property and natural 

resources.
12

• DO#35A: Sale or Lease of Park Services, Resources or Water in Support of Activities 

Outside the Boundaries of National Park Areas: Neither the law or NPS policy obligates 

the NPS to sell or lease any services, resources or water. While this DO conditionally 

allows the NPS to authorize the sale or lease of water, the NPS’s primary responsibility 

under the Organic Act is the preservation and protection of park resources -- and the 

water dependent environment – for the enjoyment of future generations. Under this DO, 

park superintendents may exercise the Director’s authority to sell or lease park services, 

resources or water, provided that the requirements contained in the DO are met; and, the 

NPS will consider a request for use of park services, resources or water through a special 

use permit application and approval process, or through the use of a written agreement.

• Reference Manual #77: Natural Resource Management: Reference Manual #77 offers 

comprehensive guidance to NPS employees responsible for managing, conserving, and 

protecting the natural resources found in national park system units. The Manual serves 

as the primary guidance on implementing Service-wide natural resource management in 

units of the national park system. Specific natural resources pertaining to water 

addressed in the manual include the management, protection, and use of: fish and fishery 

resources, freshwater resources, marine resources, nonnative species, shorelines, and 

marine, freshwater, and barrier island resources.

Management Agencies

Management of the Arkansas River and associated waters within and adjacent to the NHS 

involves several federal and state agencies.

U. S. Army Corps of Engineers (ACOE): The ACOE serves the American public in the areas of 

environmental enhancement, navigation, flood damage reduction, water and wetlands regulation, 

recreation sites, and disaster response. The agency issues permits for the placement of 

structures, dredging and filling of navigable waters under Section 10 of the Rivers and Harbors 

Act. It also regulates the discharge of dredged or other fill into all waters of the U. S. under 

Section 404, Clean Water Act. No section 404 permit may be issued by the ACOE without a 

section 401 certification from the Colorado Department of Public Health and the Environment 

stating that the discharge of dredged or fill material will not violate state water quality standards. 

The ACOE also has enforcement authority to prohibit placement of any refuse or debris in a river 

or on the bank that may be washed into the river and obstruct navigation (Sec. 13, Rivers and 

Harbor Act). 

U. S. Fish and Wildlife Service (USFWS): The Fish and Wildlife Coordination Act of 1934 

mandates that all federal agencies consult with the USFWS on permit and license applications 

involving water development projects. Section 7 of the Endangered Species Act mandates that 

all federal agencies consult with the USFWS to ensure that actions do not jeopardize federally 

listed species. 

U.S. Environmental Protection Agency (EPA): The EPA establishes standards for water quality 

management, drinking water safety, solid and hazardous waste disposal, toxic substance 

management, air quality control and general environmental quality review. Most enforcement is 
13

delegated to the states with EPA oversight. The EPA may veto a 404 permit, and it may initiate 

the lead federal role for certain cases. In Colorado the primary enforcement role for water 

quality is filled by the Colorado Department of Public Health and the Environment.

U.S. Geological Survey (USGS): The USGS is primarily responsible for collecting data on 

natural resources and the physical environment. This includes information on geological and 

biological resources, water resources, maps and mapping, and earthquakes and other natural 

disasters. 

Natural Resources Conservation Service (NRCS): The NRCS provides technical and financial 

assistance to help agricultural producers and others care for the land. NRCS helps landowners 

develop conservation plans, conducts soil surveys, and conservation needs assessments. Specific 

Colorado Programs include grassland reserve, emergency watershed protection, small watershed, 

wetlands reserve, and wildlife habitat incentive. The La Junta, CO Area 3 office of the NRCS 

serves southeastern Colorado. The NRCS is developing Rapid Watershed Assessments (RWAs) 

to provide natural resource snapshots and overviews of each of Colorado’s 8-digit Hydrologic 

Unit Codes. A RWA was developed in 2007 (NRCS 2007) for the Upper Arkansas-Lake 

Meredith watershed (HUC 11020005) where the NHS resides 

(http://www.co.nrcs.usda.gov/technical/WaterRes/LakeMerdithRWA.html).

Colorado Department of Public Health and the Environment (CDPHE): The Department

oversees the protection of the state’s waters and is charged with conserving the state’s waters and 

protecting, maintaining, and improving their quality for the wildlife and aquatic life for domestic, 

agricultural, industrial, recreational, and other beneficial uses. The Water Quality Control 

Commission (WQCC) is the administrative agency responsible for developing specific state 

water quality policies. The WQCC adopts water quality classifications and standards for surface 

and ground waters of the state, as well as various regulations aimed at achieving compliance with 

those classifications and standards. The Water Quality Division of the CDPHE serves as staff to 

the Commission and provides them with recommendations based on assessment of the state’s 

waters. Within the Department of Natural Resources, the Division of Water Resources, headed 

by the State Engineer, ensures the competent distribution of water, and administers water rights 

through the appropriation doctrine. This division also controls permits for ground water wells, 

provides water supply statistics, and surface flow data. 

The state notes nine designated uses of water including two levels each for Aquatic Cold Water 

and Warm Water, domestic water supply, and three different uses for Recreation and 

Agriculture. Colorado does not have a list of Tier III waters (highest water quality and 

protection), but instead refers to them as Outstanding Waters. The State has no stream flow or 

biological criteria or guidance with which to protect existing uses. 

Colorado Water Conservation Board (CWCB): The CWCB represents each major water basin, 

Denver, and other state agencies in a joint effort to use water wisely and protect Colorado water 

for future generations. The CWCB consists of 15 members. Eight voting members represent the 

state’s major water basins, including the Arkansas River. Services and programs of the CWCB 

include, among many, grants, loans, technical assistance (e.g., water conservation planning, 

drought mitigation planning, mapping and GIS), stream flow monitoring, floodplain mapping, 
14

instream flow, and salinity control. The CWCB ensures the development, protection, and 

management of Colorado’s waters. It is the only entity that can hold an instream water right. 

Colorado Division of Wildlife: The Division of Wildlife manages the state's wildlife species. It 

regulates hunting and fishing activities by issuing licenses and enforcing regulations. The 

Division also manages more than 230 wildlife areas for public recreation, conducts research to 

improve wildlife management activities, provides technical assistance to private and other public 

landowners concerning wildlife and habitat management, and develops programs to protect and 

recover threatened and endangered species. Colorado statutes require the Division to operate 

under the jurisdiction of the Colorado Wildlife Commission. The Commission is responsible for 

all wildlife management, for licensing requirements, and for the promulgation of rules, 

regulations, and orders concerning wildlife programs. It also establishes broad, long-term policy 

statements that provide direction to the Division for purposes of managing wildlife resources in 

Colorado.

Colorado Division of Water Resources: Ground water administration and enforcement is one of 

the primary responsibilities of the Division of Water Resources, led by the State Engineer. The 

State Engineer also provides staff to assist in technical support to the Colorado Ground Water 

Commission, in the exercise of its duties in the designated basins, generally located on the 

eastern plains of Colorado. Well permits for wells in these basins are evaluated by the staff of 

the State Engineer based on Commission rules.

The Division is empowered to administer all water rights according to the Appropriation 

Doctrine (in short, 1st in time, 1st in right). This includes releasing water from reservoirs to 

satisfy senior water users in Colorado and meeting the obligations to Kansas under the Arkansas 

River Compact. Most of this work is done by Division offices located in the seven major river 

basins of the state. These offices employ water commissioners to ensure the priority system is 

followed, enforcing the decrees and water laws of the State of Colorado. The Colorado Ground 

Water Law established the permitting requirement of ground water wells, and by 1969, surface 

and ground water rights were administered together.

Stakeholders at the Local Level

Arkansas River Basin Water Forum: The Forum, first held in 1995, was developed as a means to 

bring together the diverse water interests to explain their views and engage in open dialogue 

about water resource issues in the basin. Through this dialogue the Forum seeks to find common 

ground between primary water users in the basin.

Southeast Colorado Resource Conservation and Development Council: This non-profit 

organization works with local units of government, community organizations, groups, and 

individuals to coordinate technical and financial assistance to meet the needs of the local area. 

The vision of the council is to have an active, progressive network of communities working 

together for the good of all citizens through creative projects and activities that develop the 

regional economy, enhance our environment, and preserve our heritage. The council concentrates 

on areas of land management, water management, land conservation, and community 

development. The council recently developed a Lower Arkansas Watershed Plan (Tetra Tech 

2007; see below).
15

Southeast Colorado Water Conservancy District: The Southeastern Colorado Water Conservancy 

District was created under Colorado State Statutes in 1958 for the purpose of developing and 

administering the Fryingpan-Arkansas Project. The District extends along the Arkansas River 

from Buena Vista to Lamar, and along Fountain Creek from Colorado Springs to Pueblo. The 

District is the legal agency responsible for repayment of the reimbursable costs of the project. In 

addition to administering this repayment responsibility, the District makes supplemental water 

from the Fryingpan-Arkansas Project available for use on irrigated land under various private 

and mutual ditch companies, and for use by municipal and domestic water suppliers who directly 

serve the District's approximately constituents.

Lower Arkansas Valley Water Conservancy District: In November 2002, voters in Pueblo, 

Otero, Crowley, Bent and Prowers counties approved an initiative to form the Lower Arkansas 

Valley Water Conservancy District. The Board of Directors was appointed that December, and 

the new District held its first meeting. The mission of the district is to acquire, retain and 

conserve water flowing in the Arkansas River and its tributaries; to insure that all water will 

remain in the valley for socioeconomic benefit of the District citizens; and to participate in 

water-related projects that will embody thoughtful conservation, responsible growth, and 

beneficial water usage within the Lower Arkansas Valley.

Colorado Water Protective and Development Association (CWPDA): CWPDA is a 501-C12 

non-profit organization, incorporated in the State of Colorado in 1965. The stated primary 

purpose of the association is to protect and develop underground and surface waters of the 

Arkansas River Basin. CWPDA has approximately 600 members, including the NHS,

representing approximately 1336 wells. The NHS pays fees to the CWPDA to include its wells 

in the Association. The membership is composed of individuals, corporations, municipalities, 

and other entities that own or control wells within the Arkansas River Basin. CWPDA's 

municipal members provide water to about 38,000 people and irrigation wells of its members 

provided sole source and supplemental irrigation water to over 71,000 acres. CWPDA municipal 

members are primarily the agricultural communities between Fowler and Las Animas.

Arkansas River Watershed Invasive Plant Plan (ARKWIPP): ARKWIPP was founded with the 

mission to offer landowners and land managers reliable information regarding invasive plants 

such as tamarisk and viable ways in which to join the control and restoration process in the 

Arkansas River Basin. The working goal of this group is a restored Arkansas River riparian 

ecosystem. The NHS is member of this group.

Related Management Plans and Programs 

Tetra Tech (2007) developed the Lower Arkansas Watershed Plan for the Southeast Colorado 

Resource Conservation and Development Council in Lamar, CO. The planning process was a 

cooperative effort and the NHS is a stakeholder/partner in this plan. The plan recognizes the 

agricultural and recreational history of the lower Arkansas River watershed, and the vast canal 

systems that have diverted and distributed water of the Arkansas River in the seven-county 

region for over a hundred years. In doing so, this plan’s focus is on identification of water quality 

issues and reducing pollutants through identification and implementation of management 

strategies and solutions. The plan’s vision is to develop the blueprint that will integrate 

watershed goals for sustainable community and agricultural development, water supply, 

fisheries, habitat preservation, flood control and recreation, and wildlife habitat to support water 
16

quality improvement in the Lower Arkansas River basin. Four goals and a number of 

measurable objectives to achieve the goals support that vision.

Bent’s Old Fort NHS is one of 11 park units that comprised the Southern Plains Inventory and 

Monitoring Network (SOPN), one of 32 similar networks nationwide. These inventory and 

monitoring networks are part of an effort in the National Park Service to develop a stronger 

scientific basis for stewardship and management of natural resources across the national park 

system. A large part of this scientific basis is the development of vital signs. Vital signs are a 

subset of physical, chemical, and biological elements and processes of park ecosystems that are 

selected to represent the overall health or condition of a park’s natural resources, known or 

hypothesized effects of stressors, or elements that have important human values. They are the 

key elements that indicate the health of an ecosystem. Vital signs can be any feature of the 

environment that can be measured or estimated and that provide insights into the state of the 

ecosystem. 

The SOPN has identified 11 vital signs for the network park units, four of which have 

importance to water resources: ground water levels; surface water quantity and water quality; 

wetland vegetation communities; and early detection of exotic plants

(http://science.nature.nps.gov/im/units/sopn/monitoring.cfm). Texas State University (2007) recommended 

monitoring activities with regard to ground water, surface water quantity, and surface water 

quality for the NHS. No specific recommendations to the NHS have been made with regard to 

wetland vegetation communities and early detection of exotic plants.
17

Description of Resources

Climate 

The climate of southeastern Colorado is semiarid -- many years are drier than average and some 

years receive only half or less the long-term average for precipitation. The region of short-grass 

prairie seems almost always in or on the verge of drought, and multi-year droughts occur on a 

10-20 year cycle (Perkins et al. 2005a,b). Some of the worst multi-year droughts occurred in the 

1930s, mid-1950s, 1970s and early 2000s. The climate is characterized by low relative humidity, 

abundant sunshine, infrequent rains and snow, moderate to high wind movement, and a large 

daily and seasonal range in temperature. Hot, dry summers contribute to dry soils and the 

potential for soil erosion. Rainfall occurs as frontal storms in the spring and early summer and 

high intensity, convective thunderstorms occur in late summer; such rainfall is frequently limited 

to a small geographical area. However, much of the area is more directly dependent on 

mountain-based snowfall and storage than on rainfall. 

From 1982-2005, the annual, average maximum and minimum temperatures for La Junta were 

70.8o F and 39.2o F, respectively (Table 1). From June to August the average maximum 

temperature is 91o F while the average minimum temperature from December to February is 15o

F. For the same period of record, the annual precipitation averaged approximately 15.3 inches 

(Table 1). An important feature of the precipitation is its seasonality; approximately, 70 percent 

of the precipitation falls during April-October and only 10 percent falls from NovemberFebruary. Evaporation during the growing season (April-October) exceeds precipitation, thus

irrigation of crops is needed. 

Table 1. Monthly climate summary for the La Junta, CO station (#054726) from 1982-2005 (from 

http://www.wrcc.dri.edu).

______________________________________________________________________________

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual

Average Max. 

Temperature (o 49.3 F) 52.3 60.3 68.9 78.8 89.2 95.1 92.4 84.4 72.3 57.6 48.7 70.8 

Average Min. 

Temperature (

o 18.0 F) 21.0 29.1 37.3 48.2 57.7 63.5 61.8 52.1 37.4 26.3 17.7 39.2 

Average Total 

Precipitation (in.) 0.48 0.49 1.26 1.68 2.06 1.71 2.46 1.97 0.97 1.00 0.74 0.45 15.29 

Average Total Snow

Fall (in.) 4.4 4.3 4.6 2.2 0.4 0.0 0.0 0.0 0.2 1.5 3.6 5.1 26.3 

Average Snow Depth 

(in.) 1 1 0 0 0 0 0 0 0 0 0 1 0 

____________________________________________________________________________________

Land Use

Irrigation and floodplain soils in the lower Arkansas River valley have resulted in some of the 

most productive agricultural lands in Colorado for growing onions, cantaloupe, watermelons, 

peppers, tomatoes, cucumbers, alfalfa, corn and wheat. Beyond the valley floor, the watershed 

turns to short grass prairie with the major form of land use being livestock production.
18

The majority of land surrounding the NHS is zoned as agricultural, with some portions 

rowcropped and others grazed (NPS 2005). The eastern boundary of the NHS is shared with a 

400-acre state wildlife area with seasonal hunts and low intensity rowcropping. State Highway

194 forms the northern boundary while US 50 forms the southern boundary.

Approximately 483 acres within the NHS have been previously disturbed by either cattle grazing 

(primarily south of Arkansas River), irrigated crops (primarily north of Arkansas River), or 

impacted by fire and/or exotic plant species infestations prior to federal ownership. Sixty-eight 

acres on the north side have been restored to native grasses.

Visitor use of the NHS peaked in the late 1970s, dropped and stabilized from the early 1980s to 

late 1990s, and maintained approximately 30,000 annual visitors from 2000-2006 (Figure 3). A 

picnic area just inside the main park gate is currently available for daytime use. Response from 

visitor surveys conducted the past couple years indicates public interest in some type of 

overnight camping facility, either tent sites or RV parking, available in the park. 

Figure 3. Average annual visitation in thousands for Bent’s Old Fort National Historic Site, 1964-2006 

(Bent’s Old Fort NHS visitation statistics).

The NHS has two historic trails. The paved 1⁄4-mile walkway leading from the visitor parking 

lot to the fort and an interpretive trail (1.4 mi loop) from the fort through the cottonwood grove,

around a large wetland and back to the visitor parking lot. Visitor use is concentrated on the 

north side of the NHS.

The NHS lands south of the Arkansas River (approximately 450 acres) consist of the riparian 

area along the river and abandoned farmland. Presently, these lands are not developed for visitor 

use, and no official public access exists. A system of fire roads through this area is used by NHS 

resource management staff. There is a possibility of a developed trail from La Junta to this area 

of the NHS through a cooperative effort with local communities and the NPS Rivers, Trails and 

Conservation Assistance Program (Wallner 2006). Access for recreational activities along the 

Arkansas River, such as fishing and boating, are not available through the park. This lack of 

0

20,000

40,000

60,000

80,000

100,000

120,000

1960 1970 1980 1990 2000 2010

Year

Visitation
19

public access is largely due to the river’s classification as an Aquatic Life Warm Water - Class 2 

waterway (Fran Pannebaker, Bent’s Old Fort NHS, pers. comm. 2007). This class of waterway 

includes waters that are not capable of sustaining a wide variety of warm water biota, including 

sensitive species, due to physical habitat, water flows or levels, or uncorrectable water quality 

conditions that result in substantial impairment of the abundance and diversity of species.

Physiography, Geology, Soils, and Vegetation

The NHS lies in the Colorado Piedmont section of the Great Plains Physiographic Province 

(Fenneman and Johnson 1946). The Colorado Piedmont ranges in elevations from 3,975 ft at the 

point where the Arkansas River enters Bent County (immediately east of Otero County) to 5,200 

ft north of Delhi, CO. Generally, the area around the NHS consists of flat to gently rolling 

surfaces with steep intervening slopes (NPS 2005). The NHS (4035 ft in elevation) includes an 

active floodplain and a series of stepped river terraces, shaped by the hydro-geomorphic effect of 

the Arkansas River. 

Changes in channel gradient, discharge or sediment load can lead to a river channel incising its 

floodplain. The original floodplain is abandoned and is left as a relatively flat bench, known as a 

river terrace, which is separated from the new floodplain below a relatively steep slope (NPS 

2005). Bent’s Old Fort sits on such a terrace (Figure 4; elevation > 4000 ft).

NPS (2005), using Weist et al. (1965) as the source, mapped and described the rock units in the 

vicinity of NHS. The Bedrock of the NHS is the Bridge Creek Limestone, a member of the 

Greenhorn Limestone Formation. Readers should consult NPS (2005) for a detailed mapping 

and description of the structural geology of the NHS; however, NPS (2005) provided a less 

detailed map that describes the surficial geology of the NHS in terms of alluvium, terrace 

deposits, overbank fines, and saturated soil (see Figure 5); these are primarily alluvial deposits of 

Wisconsin age that are overlaid with more recent alluvial deposits (NPS 2005). 

Soils in the NHS belong to the Rocky Ford-Numa-Kornman soil association that represents 

recent alluvial deposits (Stevens et al. 2007; Figure 6). These soils consist of deep, nearly level, 

well drained clay loam soils or silty-clay, sandy soils on river bottom lower plains. Bankard 

Sand occurs nearest to the river, deposited by flood waters (Figure 5). This sand is very well 

drained and supports cottonwoods, willows, and invasive tamarisk. The mature upper terrace 

exhibits a parent soil of thick, slit clay loam over a silt loam subsoil. The lower river terrace 

consists of nearly level, somewhat poorly drained, slightly saline, and clayey to sandy soils. The 

parent layer is about 12 inches thick and is generally high in organic matter. These soils are 

subject to occasional flooding. The subsoil is slowly permeable and poorly aerated. Salt tolerant 

plants, such as saltgrass (Distichlis spicata) and alkali sacaton (Sporobolus airoides), grow well 

on these soils.

The NHS is within the Great Plains – Palouse Steppe Ecological Province and the short-grass 

prairie ecoregion (NPS 2005). This part of the short-grass prairie ecoregion is dominated by 

buffalo grass (Buchloe dactyloides) and blue gramma grass (Bouteloua gracilis). The vegetation 

of the NHS is typical of lower Arkansas River valley (Figure 7). The banks of the river are lined 

with narrow bands of coyote willow (Salix exigua). The rest of the floodplain supports plains 

cottonwood (Populus deltoides) gallery forests with an understory of inland saltgrass (D.
20

Figure 4. Aerial photograph (upper; circa 1993) and topographic map (lower; circa 1953) of Bent’s Old 

Fort National Historic Site, showing the location of the fort on a river terrace.
21

Figure 5. Surficial geology of Bent’s Old Fort NHS (from NPS 2005).
22

Figure 6. Soils of Bent’s Old Fort NHS (from Stevens et al. 2007).
23

Figure 7. Vegetation map for Bent’s Old Fort NHS (from Stevens et al. 2007).
24

spicata) and alkali sacaton (Sporobolus airoides). In some areas, the cottonwoods are sparse and 

grade into grassy meadows. Along the terraces, the vegetation transitions to shortgrass prairie. 

The habitat along the Arkansas River at the NHS contains large occurrences of globally rare

plains cottonwood ecosystems ( www.cnhp.colostate.edu/.../L4_PCAArkansas%20River%20at%20Bent's%20Fort_7-23-2010.pdf). These cottonwood communities are known 

only from the lower Arkansas and Cimarron river watersheds in Colorado, Kansas and 

Oklahoma. 

River Geomorphology

The current Arkansas River in the area of the NHS is an alluvial, sand-bottomed, broadly 

meandering, perennial river. The average gradient is approximately 6.7 ft/mile. Over a linear 

distance of 3 miles, the river meanders nearly 6 miles. The river’s meanders are developed on a 

floodplain that to the north of the river is approximately 1 mile in width, very flat and bordered 

by low bluffs or hills. The floodplain to the south is 0.25 to 0.5 miles wide. Overall, the 

floodplain is developed in unconsolidated materials underlain by 30 to 40 feet of sediment. The 

sediment load is moderately heavy – largely of silt and sand. The river has been aggrading for 

the past several decades in the area between La Junta and John Martin Dam (30 miles 

downstream) (Watts and Lindner-Lunsford 1992; Gates et al. 2006) . The natural flow regime of 

the Arkansas River was altered by the construction of the Pueblo Dam and Reservoir

(approximately 60 miles upstream) in 1965. 

As the hydrology of the river changed from intermittent to perennial with the advent of irrigation

(Nadler and Schumm 1981), the floodplain saw a concomitant change in the types and amount of 

vegetation. Historically woody vegetation was sparse along the river (Swenson 1970, Nadler 

and Schumm 1981). Floodplain vegetation is much denser today because higher soil moisture is 

sustained from a higher water table associated with perennial flow. Additionally, the 

introduction of exotic salt cedar (Tamarix ramosissima), a phreatophyte, disrupted the vegetative 

dynamics of the floodplain. Significant morphological changes were wrought along the 

Arkansas River because of these hydrologic and vegetative changes. Droughts, coupled with a 

decrease in sediment supply due to irrigation diversion and the construction of dams also 

affected the channels. All of these factors acted to stabilize an otherwise active channel 

morphology.

Because of these changes, Nadler and Schumm (1981) described the Arkansas River in eastern 

Colorado as a river that has undergone a metamorphosis. Schumm (1969) defined river 

metamorphosis as a complete change of river morphology, for example, from meandering to 

braided and vice versa. The Arkansas River in the 19th century was wide, shallow and braided; 

the river today is defined by different channel characteristics (Table 2). 

Figure 8 depicts the manner of river metamorphosis at Bent’s Old Fort National Historic Site. 

Point-bar stabilization and meander-loop enlargement are primary characteristics of this 

hypothesis. Nadler and Schumm (1981) describe the metamorphosis as follows:

Perennial flows, droughts and especially dense salt-cedar growth were major factors 

leading to the metamorphosis. Salt cedar colonized the channel below mean high water 

level and stabilized the point bars during the drought of the 1930s. This process allowed 

meander loops to enlarge as channel width decreased. At elevation A [Figure 8] the 
25

alluvium becomes coarser-grained toward the channel as expected; whereas, at elevation 

C it becomes finer-grained from right to left. The change to finer-grained sediment is the 

result of a change in the type of sediment transported through the reach. This change is 

the result of the incision of Timpas Creek, a deeply incised channel that introduced a 

large suspended load into the Arkansas River.

The NHS was recently (2004) successful in the eradication of salt cedar from within its 

boundaries. It remains to be seen how the removal of salt cedar manifests into changes, if any, in 

river channel morphology and the magnitude of those changes. 

Nadler and Schumm (1981) noted that the change from intermittent to perennial flow in the 

Arkansas River and the resulting shift from a braided to meandering channel was analogous to a 

change in climate. Usually, changes in flood peaks or mean annual discharge explain river 

response, but in the case of the Arkansas River at the NHS, a change in discharge frequency 

resulted in major channel adjustments. 

Table 2. Changes in fluvial geomorphologic features of the Arkansas River at Bent’s Old Fort National 

Historic Site, 1870-1977 (adapted from Nadler and Schumm 1981). See Nadler and Schumm (1981) for 

variable definitions.

Variable 1870 1892 1926 1952 1977

% silt-clay 5.01

Median 

grain size 

(mm/Φ)

1.27/-0.344 0.248/2.01

0

Sediment 

sorting (Φ)

2.301 0.618

Vegetation Large cottonwoods, little 

underbrush, no salt cedars

Salt cedars, cottonwoods, willows

Valley slope .0016 .0018

Channel 

slope

.0013 .0014 .0015 .0010

Sinuosity 1.20 1.10 1.21 1.84 1.89

Width (m) 185 225 225 45 30

Width/depth 

ratio

Greater than 17 17

Floodplain 

construction

Point bar formation

Channel 

change

Braided to meandering channel

MWH (2005) recently classified segments of the lower Arkansas River based on the geomorphic 

characterization of Rosgen (1996). Rosgen’s classification is based on four hierarchical levels; 

MWH used only Levels I and II to describe the morphology of the lower Arkansas River. Level 

I classifies stream segments based on channel slope, channel shape, and channel patterns. The 

Level II classification considers factors such as entrenchment ratio, width/depth ratio, sinuosity, 
26

channel slope, and channel materials. The last segment classified by MWH (2005) ended at La 

Junta – it is the opinion of the authors that the segment of the river that includes the NHS would 

be classified the same as that of the segment ending at La Junta. That classification would be, in 

Rosgen’s terminology, a C5c stream segment. This represents a single-threaded channel that is 

slightly entrenched, has a moderate width/depth ratio and a moderate sinuosity, with a slope that 

is <0.001, and a sand substrate. Such a classification means that the current Arkansas River of 

the NHS would have a very high sensitivity to disturbance with a fair recovery potential. In 

addition, it would also have a very high potential for stream bank erosion, very high sediment 

supply, and a very high potential for vegetation to control the width/depth ratio (MHW 2005). 

The Rosgen stream geomorphic classification represents a formalized, index-based approach that 

incorporates the basic variables described by Nadler and Schumm (1981). It allows one to 

typecast a river segment for how that segment may respond to various restoration techniques.

Figure 8. Hypothesized metamorphosis in the Arkansas River at Bent’s Old Fort National Historic Site 

(taken from Figures 12 and 13 in Nadler and Schumm 1981). Upper: A – pre-1900 channel; B – 1926 

channel; C– channel between 1926 and 1953; D – modern channel. Lower: cross-sectional changes. 

Line 1 – 1926 channel location; Lines 2, 3 and 4 – transitional channel locations; Line 5 – 1977 channel 

location.
27

Hydrogeology

The primary aquifer along the lower Arkansas River of Colorado is the alluvial aquifer 

(http://www.geosurvey.state.co.us/wateratlas). With depths up to 250 ft, this Quaternary age alluvium 

extends along the Arkansas River for 150 miles from Pueblo, CO to the Kansas state line (MWH 

2005). The alluvial aquifer consists of unconsolidated river-deposited sediments (a 

heterogeneous mix of sands, gravels, silts, and clays). It is an unconfined, water-table aquifer in 

direct hydraulic connection with the Arkansas River surface water, and is underlain by relatively 

impermeable Cretaceous bedrock. Water table depth ranges from approximately 5 to 30 ft 

below ground surface along much of the lower river. Over 3,400 wells have been installed in 

the lower Arkansas River alluvium, and over 90 percent of these wells are completed at depths

less than 120 ft below ground surface with an average depth of only 58 ft

(http://www.geosurvey.state.co.us/wateratlas). General basin wide hydraulic characteristics for the lower 

Arkansas River alluvium include: transmissivity of 2,000-60,000 ft2

/day; hydraulic conductivity 

of 70-1,200 ft/day with an average of 530 ft/day; discharge of 10-4,000 gallons per minute (gpm) 

with a mean of 360 gpm; specific capacity of 7-54 gpm/ft drawdown; and specific yield of 0.13-

0.20 (http://www.geosurvey.state.co.us/wateratlas).

In most areas, water table depth in the alluvial aquifer is affected by proximity to the Arkansas 

River or variability in agricultural use (approximately 2 million acre-feet of river water were 

diverted for irrigation in 1998). From 1971 to 2000, wells closer to the river had a higher, less 

variable water table (MWH 2005). For that time period in Otero and Crowley counties, water 

table depth for wells close to the Arkansas River ranged from 6 to 25 ft below ground surface 

and for wells farther from the river from 21 to 44 ft below ground surface (MHW 2005). Greater 

than average precipitation from 1982-1999 is a potential cause of increased water table elevation 

during this period (USGS 2002). Ground water withdrawals are lower during wet years and 

infiltration is higher, resulting in a higher water table (MHW 2005).

Weist et al. (1965) found that the alluvial aquifer near the NHS consists of Holocene and

Pleistocene alluvial deposits. This aquifer is relatively shallow, unconfined, and highly 

transmissive (Watts and Lindner-Lunsford 1992); the ground water gradient (easterly direction) 

is approximately 6 ft/mi in the La Junta area (MHC 2005). Because the Arkansas River partially 

penetrates the aquifer, it acts as both a source of recharge or discharge to the aquifer (Watts and 

Lindner-Lunsford 1992, NPS 2005). Recharge to the aquifer is through leakage from the 

Arkansas River (e.g., short-term increases in river stage lead to short-term increases in water 

table elevation in wells near the river) and Fort Lyon Canal (leakage increases with increasing 

stage), deep percolation of irrigation water and precipitation, and underflow. The Fort Lyon 

Canal is unlined and has a direct relation to ground water levels. Bossong (2000) reported 

conveyance losses for the canal of up to 15 ac-ft/day/canal mile. The Fryingpan-Arkansas 

Project and other water development projects that import water to the basin have increased 

stream flow in the lower Arkansas River, further enhancing recharge (MWH 2005).

Discharges from the aquifer include leakage to the Arkansas River, pumpage for municipal, 

irrigation and industrial supplies, evapotranspiration, and underflow. The long-term mean for 

ground water withdrawals from 1972-1994 in the La Junta area was 1.64 ft/yr for municipal and 

irrigation use (Bossong 2000). Additionally important is the aggradation of the Arkansas River 

bed, which increases river stage and temporarily increases leakage from the river to the aquifer 
28

(NPS 2005). During high river flows, a local reversal of the hydraulic gradient between the 

alluvial aquifer and the Arkansas River can occur (NPS 2005). Watts and Lindner-Lunsford 

(1992) and Bossong (2000) noted the fluctuation of the water table over the last three decades of 

the 20th century -- the decline of water levels in the 1970s corresponded with a period of reduced 

flow in the Fort Lyon Canal (see Figure 15 and associated discussion) while water level 

increases of the 1980s correlated with increased flow in the Canal, increased surface water 

applications, and reduced ground water withdrawals (Bossong 2000). As mentioned above, an 

increase in precipitation over the long-term mean may be a proximate cause for the water table 

increase in the 1980s.

Woods et al. (2002) conducted a short-term study (March-September 2001) into the cause of 

basement flooding at Bent’s Old Fort. The cause of this flooding had been attributed to rising 

water table levels in the late 1990s and early 2000s (Bossong 2000). The purpose of the study 

was to determine which of several factors (i.e., decline in groundwater pumping; increased 

seepage from Fort Lyon Canal; increased deep percolation of irrigation water; and greater 

leakage from Arkansas River to the aquifer due to river bed aggradation) was primarily 

responsible for causing flooding of the Fort’s basement. They installed a network of 15 wells to 

monitor ground water elevation. Upland wells had relatively stable water elevations and were 

unresponsive to river stage changes; however, wells closest to the Arkansas River were more 

variable and distinctly responsive to river stage changes. Furthermore, the reach of the Arkansas 

River in the NHS was a gaining reach – the ground water gradient was towards the river because 

water table levels were higher than the river stage. Thus, river stage was less of an influence on 

water table levels along this river reach than in the area near La Junta (Bossong 2000). 

Ground Water Quality

All ground water at the NHS is classed as sodium-calcium-sulfate-bicarbonate in character (NPS 

2005) and is rated hard to very hard (Weist et al. 1965).

The Colorado Department of Public Health and the Environment (2006) determined that ground 

water in the alluvial aquifer of the lower Arkansas River basin meets primary and secondary 

federal and state domestic or municipal water supply standards, based on a detailed analysis of 

wells of the aquifer. Only 1 out of 20 wells had nitrate concentrations that exceeded the water 

quality standard of 10 mg/L. Detections of herbicides and pesticides were low and all detections 

of pesticides were at concentrations below the water quality standard and health advisory levels. 

Similar to surface water, the alluvial ground water frequently exceeds the high salinity hazard 

threshold for agriculture of 50 μS/cm and the 500 mg/L drinking water secondary maximum 

concentration level (CDPHE 2002). 

From 1999-2005 Gates et al. (2006) studied salinity as a function of specific conductance 

concentrations in the ground water (from approximately 90 wells) of a large study area that 

included the NHS. Mean specific conductance was 3,275 μS/cm, well above the agriculturallybased very high salinity hazard of 2,250 μS/cm, and demonstrated high spatial variability over 

the range of wells sample (Figure 9). Irrigation frequency and geology are two of several factors 

that could cause this variability (Gates et al. 2006). 

Ground water salinity has increased in the Arkansas River alluvial aquifer since the 1970s (Gates 

et al. 2006). Gates et al. listed the following as possible reasons: 1) reduced ground water
29

pumping; 2) gains in seepage losses from irrigation canals; 3) failures of tile drains installed in 

the 1930s; 4) changes in river operations,; and 4) dissolution of salts from salt-bearing geologic 

formations that form the base underneath the alluvial aquifer. 

Figure 9. Mean and spatial variation of specific conductance in the lower Arkansas River alluvial ground 

water (from MWH 2008). Based on samples from 90 wells.

Gates et al. (2006) found that ground water concentrations of selenium averaged approximately 

57.7 μg/L. For comparison, the state chronic standard for aquatic habitat of surface waters is 4.5

μg/L. They found that regional geologic formations had a strong influence on ground water 

selenium concentrations. There was an inverse correlation between selenium concentration and 

distance to the closest upstream shale, and selenium concentrations from samples taken from 

shale-derived material had a median concentration of 30.8 μg/L; whereas alluvial material had a 

median concentration of 12.2 μg/L. Additionally, they demonstrated a strong correlation 

between dissolved selenium and both total dissolved solids and uranium in ground water. 

Aquifers overlying or adjacent to Cretaceous age marine shales and sedimentary rock formations 

typically have higher ground water concentrations of salinity, iron, and selenium (Seiler et al.

1999, Burkhalter and Gates 2005). Figure 10 shows the location and extent of Cretaceous 

marine shales in the Arkansas River Basin. The Pierre Shale is known to be seleniferous. 

The lines of evidence for other Cretaceous marine shales (e.g., Carlile and Graneros shales and 

Greenhorn limestone) being seleniferous is indirect (Seiler et al. 1999). For example, there are

ground water hotspots throughout the Arkansas River basin. Evaporative concentration of 

selenium would result in more uniform concentrations basin-wide, thus it appears that these 

selenium hotspots are geologically derived (Donnelly and Gates 2005).

Surface Water Hydrology

The Arkansas River basin is the largest basin in Colorado (Figure 11), covering 28,286 mi2 (> 18 

million acres), yet only 20 percent of the state’s population occupies this area. The river 

originates in the mountains near Leadville and continues to the state line in Kansas, with an 

approximate flow of 1 million ac-ft/yr. Major tributaries include the Purgatoire, Huerfano, 
30

Cucharas, and Apishipa rivers. The basin is usually characterized as two subsections, the upper 

and lower Arkansas River. 

Figure 10. Locations of Cretaceous marine shale in the Arkansas River Basin of Colorado (from MWH 

2008).

The upper Arkansas River of Colorado is generally considered to be from the mountain source to 

Pueblo Dam, while the lower section continues from the Pueblo Dam to the Kansas state line. 

The upper Arkansas contains mountain streams and tributaries and often runs colder and quicker 

due to fewer diversions; it is utilized mainly for municipal drinking water supplies. The lower 

Arkansas River of Colorado is a wider, shallower flowing river heavily diverted in canals and 

reservoirs for agricultural and municipal purposes. Canals contribute largely to the hydrologic 

regime with diversions re-routing about 2 million ac-ft/yr of water for irrigation in the lower 

Arkansas River basin of Colorado. 

The NHS is in the Upper Arkansas Lake Meredith watershed (HUC 1102000, as defined by the 

U.S. Geological Survey; Figure 12). In this case ‘Upper Arkansas’ refers to the upper part of the 

overall Arkansas River watershed. Within this watershed there are approximately 1,413,670 

acres of land utilized for farming or ranching. The population of this watershed is slightly 

greater than 100,000.
31

Figure 11. The Arkansas River basin in Colorado (from Tetra Tech 2007).

Drainage problems usually appear in intensively-irrigated alluvial valleys within a few decades 

to a few hundred years of the commencement of large-scale irrigation. Eventually, the 

artificially high rate of application of water to land exceeds the natural rate of drainage, the water 

table rises, and artificial drainage is needed to regain an acceptable water and salt balance (Gates 

and Grismer 1989). In the lower Arkansas River valley in Colorado, saline high water tables 

began to appear in the early part of the 20th century. Installations of subsurface drains in the 

1930s seemed to alleviate the problems; however, water tables began to rise again in the 1970s. 

Watts and Lindner-Lundsford (1992) suggested that the blame be placed on increased diversions

from the river for irrigation application and associated reduction in ground water pumping. In 

the 1950s-1970s two reservoirs began operations that have drastically changed the river. 

Flushing from floods was substantially reduced and controlled releases were made from the 

reservoirs. This allowed year-round or at least prolonged supplies of water to the canals on the 

perimeter of the valley. Seepage from these canals and lower velocity in the river has caused 

sediments to deposit on the bed and the river level to rise. Recent investigations at Colorado 

State University of water levels in the reach of the Arkansas River upstream of John Martin 

Reservoir indicate an increasing trend since about 1989. The overall rise in the river level (of 

about 0.6 m) may have significantly reduced the gradient that drives drainage flows from the 

irrigated land to the river. Also, in response to the recent Kansas –Colorado court ruling, ground 

water pumping in the valley which serves to reduce water table levels has diminished.
32

Figure 12. Upper Arkansas Lake Meredith watershed (HUC 11020005) in the Arkansas River basin of 

southeastern Colorado.

The flow of the Arkansas River is perennial but highly regulated; the flow of its tributaries 

depends on precipitation and return flow from irrigation. River flow is affected by numerous 

upstream diversions and Pueblo Dam, built in 1965. The dam lies approximately 62 miles 

upstream from the NHS. For example, stream flow at Las Animas is substantially smaller than at 

the upstream sites. The downstream decrease in stream flow is attributable to irrigation 

diversions upstream of Las Animas (Lewis 1998). 

Using historical (1974-2004) instantaneous peak discharge data, MWH (2005) summarized peak 

flows for the Arkansas River at the La Junta gage site (USGS gage 07102300) as follows: 

Peak Flow Discharge (cfs)

1.5-year 2-year 10-year 50-year 100-year 500-year

2,700 4,200 14,200 29,600 38,300 64,800

The maximum recorded instantaneous peak discharge for the La Junta gage was recorded on 

June 4, 1921 at 200,000 cfs (MWH 2005). 

The Arkansas River is dominated by the seasonal snowmelt cycle; baseline flow conditions exist 

September-April followed by an increase in flow in May to a peak in June and gradually tapering 

flows until base conditions are reached in September (Figure 13). Prior to European settlement 

the Arkansas River had strongly varying, intermittent flow during each year (Figure 14), with 

very little discharge during the dry times of the year and large floods in late spring and summer. 

Following settlement of the plains, land-use practices so altered the water and sediment flows 

along the Arkansas River that the channel underwent a change in channel functioning and pattern 

(see River Geomorphology section). The primary influence was flow regulation (Pueblo and 

John Martin dams) and diversion (e.g., Fort Lyon Canal, Figures 15 and 16), which reduced 

seasonal flood peaks (Figure 14, post-1965) and increased dry-season base flow in the channels. 

For example, base flows during December-April for the period 1970-1999 increased from 1.3 to 

2+ times more that the base flows from 1912-1938 (based on data collected from La Junta stream 
33

gage). As irrigation water that was diverted and spread across agricultural fields filtered into the 

subsurface, regional water tables rose (see Hydrogeology section). The amount of sediment 

carried by the Arkansas River decreased as the reservoirs behind Pueblo and John Martin dams 

served as large settling tanks, and the smaller seasonal high flows had less energy to carry 

sediment. 

Figure 13. Representative hydrographs for the Arkansas River at La Junta, CO (USGS gage station 

07123000) (from NPS 1998).
34

Figure 14. Mean daily discharge from 1912-2007 for the Arkansas River at La Junta, CO. Pre-1960 flows 

are the closest representation of flow variability prior to European settlement. Compare the variability of 

flows pre-1965 to post-1965, the completion date for Pueblo Dam and Reservoir (from 

http://waterdata.usgs.gov/co/nwis/inventory/?site_no=07123000).

Figure 15. Map of Lower Arkansas River from Rocky Ford to John Martin Reservoir showing location of 

the Fort Lyon Canal (red) in relation to the river and Bent’s Old Fort NHS. The canal was developed in 

1886 by T.C. Henry. In the vicinity of the NHS it lies approximately 1⁄2 mile to the north. It is an earthen 

canal supplying irrigation water to farms in the lower Arkansas Valley. This earthen canal is currently use 

to supply water for agricultural irrigation and is managed by the Fort Lyon Canal Co. 
35

Figure 16. Total annual discharge of the Arkansas River at La Junta and Fort Lyon Canal,1917-1994, 

showing the disparity in flow between the two systems (from Goff et al. 1998).

A limited glimpse (1974-2006) of mean annual flows for the Arkansas River (Figure 17) 

suggests that the drought cycle in the southeastern Colorado has a recurrence interval of 

approximately 11 to 13 years.

Besides the Arkansas River, the NHS has a few small irrigation ditches, remnants of past 

agricultural use,, that are not presently used by the NHS. An active irrigation return ditch flows 

eastward along State Route 194 and empties into the Arkansas River just north of the Arch 

Wetland (see Figure 24).

Existing stream staff gages along the Arkansas River inside NHS boundaries (from the study by 

Woods et al. 2002) are not currently monitored by NHS staff., because they are consistently 

damaged by flood waters. The NHS should seek technical assistance from the Water Resources 

Division to explore the durability issue of these gages.

Surface Water Quality

The following history and description of the Arkansas River provides the necessary context for 

understanding water quality in the river. It is taken from http://www.kgs.ku.edu/Hydro/UARC/background.html

and has been slightly modified for this report.

Before settlement of the Great Plains in the 1800's, Arkansas River flows carried 

dissolved solids primarily derived from Cretaceous bedrock in southeastern Colorado and 

southwestern Kansas near the state line. The dissolved solids inputs entered the river 

from tributaries and ground-water discharge. During low and moderate flows, the river 

waters were probably slightly saline as they entered Kansas. As the flows passed through 
36

southeast Colorado, they could either recharge to or receive discharge from the alluvial 

aquifer, depending on the amount of flow and the ground-water levels in the aquifer.

Figure 17. Mean annual flow (cfs) from 1975-2006 for the Las Animas, CO gage site (USGS 07124000)

on the Arkansas River. 

High-flow conditions following dry periods would be times of greater recharge.

However, during flood conditions, the Arkansas River waters were more dilute 

and could have recharged the alluvial aquifer with fresher waters. The bank 

storage would then have been returned to the river as discharge in later dry 

periods after partially mixing with waters in the alluvium.

Beginning in the 1860's, farmers dug small ditches along the Arkansas River in 

Colorado to divert water for crop irrigation. Larger canals were then constructed 

for extensive diversion systems starting in the 1870's in Colorado.

Evapotranspiration of the diverted waters increased the salinity of ground-water 

recharge from the fields and irrigation return flows. Part of the dissolved solids in 

ground waters underlying diversion ditches and the fields irrigated by the ditch 

waters was attributed to concentrated river waters. Ground-water levels rose in 

the vicinity of the canals and ditches due to leakage. 

Irrigation from diversions of Arkansas River water in southeastern Colorado has 

increased the salinity of river water since the 1870's due to evapotranspiration 

concentration. Regulation of river flows by the John Martin Reservoir beginning 

about 1950 further increased the salinity problem through increased diversions 

and consumptive loss by evapotranspiration in southeastern Colorado. The 
37

evapotranspiration caused increases in many dissolved constituents to undesirable 

levels for water use. 

The NPS (1998) provided a baseline water quality data inventory and retrospective analysis for 

the NHS. Water quality data were retrieved from national databases (e.g., STORET) for the 

NHS and its surrounding area. The results for the study area yielded 11,722 observations for 149 

separate parameters collected by the NPS, USGS, USEPA, and CDPHE at 30 monitoring stations 

from 1901 through 1995. Approximately 54 percent of the 11,722 observations within the study 

area were collected by the CDPHE from 1901 through 1993 in the Arkansas River at the Fort 

Lyon Canal. However, no stations were located within the NHS boundary, and the three 

Arkansas River sites are all over 5 miles upstream near La Junta. Many of the monitoring 

stations represent either one-time or intensive single-year sampling efforts by the collecting 

agencies. Only five stations (three mainstem and two tributary) within the study area yielded 

longer-term records consisting of multiple observations for several important water quality 

parameters. The results of the NHS water quality criteria screen found 18 groups of parameters 

that exceeded screening criteria at least once within the study area. Dissolved oxygen, pH, 

chloride, chlorine, cadmium, copper, lead, nickel, selenium, and zinc exceeded their respective 

U.S. Environmental Protection Agency criteria for protection of freshwater aquatic life. 

Chloride, fluoride, sulfate, nitrite plus nitrate, cadmium, chromium, lead, nickel, uranium and 

zinc exceeded their respective U.S. Environmental Protection Agency drinking water criteria. 

Fecal-indicator bacteria concentrations (total coliform and fecal coliform) and turbidity exceeded 

the NPS-Water Resources Division screening limits for freshwater bathing and aquatic life. 

The NHS is in Segment COARLA01b of the Arkansas River as delineated by the CDPHE. This 

segment is classified according to the following uses: 1) Aquatic Life – Class 2 (waters that are 

not capable of sustaining a wide variety of warm water biota, due to physical habitat, water flows 

or levels, or uncorrectable water quality conditions that result in substantial impairment of the 

abundance and diversity of species); 2) Recreation – Class E (use for primary contact recreation 

or has been used for such activities since November 28, 1975); 3) Domestic Water Supply 

(waters are suitable for potable water supplies—after receiving standard treatment these waters 

will meet Colorado drinking water regulations); and 4) Agriculture (suitable for irrigation of 

crops usually grown in Colorado and not hazardous as drinking water for livestock). 

Additionally, Segment COARLA01b is a use-protected water under Colorado’s antidegradation 

designations. This means that this segment does not warrant protection provided by the 

outstanding waters designation or the antidegradation review process. Use protection provides 

the lowest protection of the three Colorado antidegradation designations.

Numeric water quality standards are assigned to water bodies to protect classified uses. Numeric 

standards can either apply on a statewide basis or to specific waters. General water quality 

standards, known as Table Value Standards (TVS) are assigned for the Arkansas River Basin in 

Regulation #42 (CDPHE 2007). Site-specific standards for segments are also assigned which 

may or may not be equal to the TVS. The water quality standards, including TVS and site 

specific standards for the Arkansas River basin are summarized at 

http://www.cdphe.state.co.us/regulations/wqccregs/ .

The State of Colorado published in 2008 Colorado’s List of Water-Quality-Limited Segments 

Requiring Total Maximum Daily Loads (TMDLs), commonly referred to as the 303(d) list. This 
38

list was prepared to fulfill section 303(d) of the Clean Water Act that requires states submit to 

the U.S. Environmental Protection Agency a list of those waters for which technology-based 

effluent limitations and other required controls are not stringent enough to implement water 

quality standards. Once listed, the State is required to prioritize these segments based on the 

severity of pollution and other factors. It will then determine the cause(s) of the water quality 

problem and allocate the responsibility for controlling the pollution. This analysis is called the 

TMDL process, and it is a pollution reduction plan that identifies the maximum amount of a 

pollutant a water body can receive without violating water quality standards. The TMDL process 

identifies both point and nonpoint sources of each pollutant and determines how much each 

source must reduce its contribution in order to meet the standard. The total of all contributions 

must be less than the maximum daily load. Subsequent to the TMDL, a detailed implementation 

plan is developed that focuses on source reduction strategies to meet water quality standards. 

The 2008 Colorado 303(d) list showed that segment COARLA01b as water quality limited for 

selenium. The development of a TMDL for this segment was also listed as a low priority. 

Previously, this segment was on the 303 (d) list for fecal coliform; however, a fecal coliformbased TMDL was completed in 1998 (NPS 2003).

Selenium is a naturally occurring semi-metallic trace element that is essential for animals in 

small doses but is toxic at high concentrations. Selenium has had adverse effects on endangered 

fish species in the Gunnison and Colorado rivers in Colorado; however, in the lower Arkansas 

River basin, there was no evidence of impacts to aquatic biota (Mueller et al. 1991), although 

some segments not only exceed selenium water quality standards, they are at levels exceeding 10 

ppb known to eliminate fish in some parts of the country. Possible explanations for these sitespecific differences in toxicity of selenium include:

• Different forms of selenium have different effects on aquatic life. The dominant form of 

selenium in water can vary based on site-specific factors (Maier et al. 1987). The 

dominant toxic form of selenium is selenite – selenite represents a small percentage of the 

selenium in the lower Arkansas River (USEPA 1998);

• Sulfate concentrations in the lower Arkansas River increase downstream of Pueblo 

(Figure 18) and may reduce selenium toxicity [see Brix et al. (2001) for a discussion of 

the sulfate/selenium toxicity relationship];

• Aquatic life in the Arkansas River Basin may have adapted to survive in waters with 

elevated selenium concentrations.

There has been considerable uncertainty regarding the appropriate selenium standards for 

different stream segments in the Arkansas River basin. The current TVS for acute and chronic 

dissolved selenium are 18.4 and 4.6 μg/L, respectively. The average selenium concentration in 

the Arkansas River Segment COARLA01b is 15.66 μg/L (Tetra Tech 2007). Figure 19 shows 

average selenium concentrations for specific locations on the Lower Arkansas River and its 

major tributaries.
39

Figure 18. Sulfate concentrations along the lower Arkansas River in Colorado (From 

http://ndis1.nrel.colostate.edu/waterquality/arkrnut/arknut.html.

Ortiz et al. (1998) found that over 90 percent of the selenium measured in the lower Arkansas 

River was in the dissolved phase. In general, selenium concentrations increased downstream 

from Pueblo Reservoir to Las Animas. Salinity in the lower Arkansas River has the same spatial 

pattern. Some of the factors causing an increase in salinity in the lower Arkansas River may also 

be responsible for increasing selenium in the downstream direction. Donnelly and Gates (1995) 

investigated relationships between water quality parameters including selenium, salinity, nitrate 

and sulfate in the lower Arkansas River. They developed a relationship between salinity and 

selenium that showed that some of the variation in selenium could be related to salinity.

Ortiz et al. (1998) also found that median dissolved selenium concentrations were generally 

largest during low flow conditions in the Arkansas River. Therefore, there is likely an inverse 

relationship between flow and dissolved selenium concentrations in the Arkansas River, a 

relationship also seen with salinity.

Figure 19. Selenium concentration in the Lower Arkansas River (upstream to downstream) and major 

tributaries (from Tetra Tech 2007). Mainstem locations are in blue and tributaries in yellow.
40

A substantial amount of the watershed of the lower Arkansas River drains over marine shale 

formations (see Figure 10). Donnelly and Gates (2005) stated that irrigation over soils derived 

from marine sedimentary rocks can accelerate dissolution and mobility of selenium into ground 

water and subsequently the Arkansas River. Additionally, crop irrigation increases the 

consumptive use in the watershed, concentrating dissolved constituents such as selenium. Ortiz 

et al. (1998) stated that local geology and irrigation return flows are the two most likely causes 

of the increasing selenium in the Arkansas River between Pueblo and Las Animas.

The lower Arkansas River is considered one of the most saline streams of its size in the U.S. due 

to excessive irrigation, seepage from earthen canals, inadequate drainage facilities, and a rising 

ground water table that leaches soluble salts (e.g. iron, sulfate, and selenium) from underlying 

geologic marine shale formations. Such conditions allow these salts to be concentrated in the 

soil and irrigation return flow. This high total dissolved solids concentration lowers the water 

quality of the Arkansas River downstream of La Junta (CDPHE 2002).

The most common measure of salinity [also referred to as total dissolved solids (TDS)] is 

specific conductance. It is a measure of the ability of water to conduct electrical current and its 

value is related to the type and concentration of ions in solution. Typically, TDS concentration is 

approximately 65 percent of the specific conductance (μS/cm), although site-specific 

relationships are usually more accurate. There is no water quality standard for salinity in the 

Arkansas River basin. EPA has set a secondary maximum concentration level (MCL) for 

drinking water of 500 mg/l TDS (approximately equal to 740 μS/cm specific conductance). 

Secondary MCLs are non-enforceable guidelines for contaminant levels at the tap. 

The specific conductance of the lower Arkansas River generally increases downstream from 

Pueblo to Las Animas (Lewis 1998, MHW 2008, Figure 20). Specific conductance is also 

inversely related to flow, e.g. low flows in December have high specific conductance (Figure 

21). The overall trend for specific conductance to increase downstream is due to the fact that 

irrigation-return flows compose an increasingly large percentage of stream flow. 

Figure 20. Specific conductance in the lower Arkansas River and major tributaries (from Tetra Tech 

2007). Mainstem locations in blue; tributaries in yellow.

Total recoverable iron is an impairment in the COARLA01a segment of the lower Arkansas 

River (CDPHE 2006), as well as in previous 303 (d) listings for the COARLA01b segment. 
41

Ortiz et al. (1998) noted elevated concentrations of total recoverable iron in the lower Arkansas 

River. They found that upstream of Las Animas, concentrations were substantially higher during 

snowmelt runoff and post-snowmelt runoff seasons. In addition, Ortiz et al. found that the major 

tributaries, such as the Apishapa River, had storm flow total iron concentrations 200-300 times 

the concentrations that occur in the Arkansas River mainstem –the likely source of iron in the 

lower Arkansas River are highly erosional tributaries.

Zielinski et al. (1995) studied dissolved uranium concentrations in the Arkansas River. They 

found that the rate of increase of dissolved uranium concentration with distance downriver 

increased markedly as the river flowed from predominately undeveloped lands underlain by 

igneous and metamorphic rocks to agriculturally developed lands underlain by marine shale and

Figure 21. Seasonal relationship of stream flow to specific conductance for the Arkansas River near 

Avondale (Lewis1998).

limestone. Additionally, they observed an abrupt increase in dissolved uranium along that 

portion of the river where river discharge is substantially reduced due to irrigation diversions, 

and where remaining flow is largely composed of irrigation return water. Dissolved uranium 

concentrations in the river and most of its tributaries exceeded the U.S. drinking water standard 

of 20 μg/L. Uranium concentrations of river water from agricultural use areas showed a strong 

positive correlation with major dissolved constituents (e.g., sodium, calcium, magnesium and 

sulfate).

Ortiz et al. (1998) found that bacteria densities at sites on the Arkansas River generally increased 

in the downstream direction and that densities were generally low compared to the water quality 

standards. Also, from 1998-2004 no samples (n=41) from the Colorado Canal to John Martin 

Reservoir segment of the Arkansas River exceeded the fecal coliform water quality standard 

(MHW 2008). However, there is no longer a water quality standard for fecal coliform in the 

lower Arkansas River because the State of Colorado has transitioned to E. coli-based water 

quality standards (CDPHE 2007). There are limited E. coli data for stations in this segment, but 

the low densities of fecal coliform in the mainstem indicate that E. coli densities are also likely 

low in the Arkansas River.
42

Floodplains, Wetlands and Riparian Areas

Lower Arkansas River valley floods may be characterized as low density, long-duration rainfall 

over a large area, or short duration thunderstorms of high intensity rainfall over a small area. 

These localized events are common in southeast Colorado and account for the presence of 

arroyos and intermittent streams.

Floods on the Arkansas River are of two general types: spring floods result from snow melt and 

are often augmented by storm runoff, and summer floods result entirely from storm runoff. 

Spring floods are characterized by moderate flow of long duration with large volumes of runoff. 

Summer floods are characterized by high flow with relatively smaller volumes of runoff. Major 

floods along the Arkansas River occurred in July 1886, June 1921, May 1955, May 1969, and 

April 1999. Much of the Lower Arkansas River floodplain has been developed for agricultural

purposes. Urban and residential development to the west of the NHS is also important with 

regard to flooding. The combination of this development along with the two major dams along 

the river has significantly altered the nature of flooding in the valley. In addition to the Arkansas 

floodplain, two local tributaries (upstream of NHS), King and Anderson arroyos, have previously 

contributed to significant floods.

According to the park’s draft General Management Plan (NPS 1994), the Colorado Water 

Conservation Board reported the flood stage heights of 12 and 14 feet above the river channel for 

the 100- and 500-year floods, respectively. The water surface elevation of the 100-year flood is 

4,002 ft NGVD (National Geodetic Vertical Datum) which is approximately the elevation of the 

lowest point of the fort grounds. The 500-year flood elevation is 4,004 feet NGVD; a flood of 

this elevation would completely inundate the fort. 

The National Weather Service has developed the Advanced Hydrologic Prediction Service 

(http://water.weather.gov/ahps2/index.php?wfo=pub). The NHS is encouraged to consult this website, 

especially during the flood season, for predictions of flooding stage heights/flows. Figures 22

and 23 are representative website plots for the U.S. Geological Survey gage at La Junta. Figure 

22 shows the stage heights from the previous three days as well as the forecasted stage heights 

for the next 5-day period. Figure 23 shows the chance of river stage exceeding various levels 

during the forecasted time period (in this case May 27 – September 23, 2010). 

For such long-range forecasts, it should be expected that conditions will change over such 

extended periods. These forecasts are updated periodically and should be consulted on a regular 

basis.

Wetlands represent transitional environments between terrestrial and aquatic systems where the 

water table is at or near the surface or the land is covered by shallow water (Cowardin et al. 

1979). Flora within these wetland systems exhibit extreme spatial variability, triggered by very 

slight changes in elevation. Temporal variability is also great because the surface water depth is 

highly influenced by changes in precipitation, evaporation and/or infiltration. 

Cowardin et al. (1979) developed a wetland classification system that is now the standard in the 

federal government. In this system, a wetland must have one or more of the following attributes: 

(1) at least periodically, the land supports predominately hydrophytes; (2) the substrate is 
43

Figure 22. Plot from the National Weather Service’s Advanced Hydrologic Prediction Service of actual 

and forecasted stage height and flow for the June 5-15, 2010 period for the La Junta gage (from 

(http://water.weather.gov/ahps2/hydrograph.php?wfo=pub&gage=lxhc2&view=1,1,1,1,1,1,1,1). 

predominately un-drained hydric soil; and (3) the substrate is non-soil and is saturated with water 

or covered by shallow water at some time during the growing season of each year.

The National Wetlands Inventory map (Hadley Quadrangle) that includes the NHS identifies the 

following wetlands based on the Cowardin et al. (1977) classification system: 1) the Arkansas

River is classified as a lower perennial, open water, riverine wetland; 2) south of the river there 

are palustrine, forested/scub/shrub (PFO/PSS) and forested/flat palustrine (PFO/PFL) wetlands; 

and, 3) north of the river there are PFO/PSS, PFO and palustrine, emergent (PEM) wetlands (see 

Figure 24).

Gionfriddo et al. (2002) conducted wetland plant surveys at the seven known wetlands in the 

NHS and found a total of 31 wetland species (the NHS now recognizes six wetlands; see Figure 

24). Tisdale-Hein (2006) concentrated on only one wetland area (Arch Wetland). The wetland 

summaries below are taken from these two studies.

The Arch Wetland (PEM/PFO; Figure 24) is a 55-acre palustrine wetland located on the second 

floodplain bench of the Arkansas River that park natural resource staff has identified as one of 

the park’s key natural resources. It is semi-permanently flooded, and is covered by a dense 

(approximately 90%), homogenous stand of cattails (Typha latifolia). In addition, cattail 

comprises at least 70 percent of the wet soil area around the wetland (Tisdale-Hein 2006). Open 

water areas in the wetland are few and water depth is around 18 inches. Cattails provide less

quality habitat than the two bulrush species at the wetland [Schoenoplectus lacustris acutus

(hardstem bulrush) and Scirpus paludosus (alkali bulrush)]. Water inflow to the wetland is from
44

Figure 23. Plot from the National Weather Service’s Advanced Hydrologic Prediction Service of river 

stage versus exceedance probability for the May 27-September 23, 2010 time period for La Junta gage 

(from http://water.weather.gov/ahps2/period.php?wfo=pub&gage=lxhc2&view=1,1,1,1,1,1,1,1&toggles=10,7,8,2,9,15,6). The 

conditional simulation (CS) line indicates the chances of the river exceeding given levels based on current 

levels. The historical simulation (HS) line indicates the chances of the river exceeding given levels based 

on the total range of past levels. For example, if the CS line is substantially above the HS line, the 

conditions are wetter than normal conditions and the chances are greater for wet conditions over the 

entire range; whereas, if the CS line is substantially below the HS line, the conditions are drier than 

normal conditions and the chances are greater for drier conditions over the entire range. When the CS 

and HS lines are very close across the entire range, the changes of the river exceeding a certain level is 

similar to the total range of past levels.

bank overflow from the Arkansas River and leakage from Fort Lyon Canal – it is this leakage 

and the concomitant water table rise that caused this wetland to increase in size during the 1980’s 

and 1990’s. This dependence means that any decrease in flow in the Fort Lyon canal could 

cause a decrease in the size of the Arch Wetland (Woods et al. 2002). In addition, upgradient 

groundwater withdrawals could reduce groundwater inflows and reduce the size of the wetland. 

The wetland has high flood attenuation and storage capability due to the dense vegetative cover 

and restricted outlet and its occurrence within the floodplain of the Arkansas River. TisdaleHein (2006) recorded 70 plant species from this wetland; 15 (22 percent) of these species are 

exotic. In contrast, Gionfriddo et al. (2002) recorded only 19 wetland plant species for this 

wetland. Tisdale-Hein noted habitat for beneficial species such as hardstem bulrush 

(Schoenoplectus lacustris acutus), alkali bulrush, prairie coneflower (Ratibida tagetes) and other 

natives, were found in Arch Wetland along with persistent exotic species such as tamarisk and 

Russian olive. Canada thistle (Cirsium arvense) is a major problem around the perimeter of the 

Arch Wetland and forms a monoculture in several areas, restricting riparian plant species 

diversity. Tisdale-Hein (2006) classified the overall health of the wetland as fair with limitations 
45

Figure 24. Locations of extant wetlands in Bent’s Old Fort NHS. Arch Wetland corresponds to the 

PFO/PEM wetland on the NWI map; Casebolt wetland to PFO/PSS; SE Old Stock Tank wetland would be 

classified as PFO/PSS; the SW Old Stock Tank wetland corresponds to PFO/PFL; the Day Wetland and 

the Day Pond, although not delineated on the NWI map, are both PEM/OW wetlands with the Day Pond 

being more open water than the Day Wetland. The seventh wetland identified by Gionfriddo et al. (2002)

occupied the former river channel. The Bank Stabilization project mitigated an erosion (head cut) problem 

in the irrigation return ditch just before it empties into the Arkansas River.
46

involving the monocultures of cattail and thistle, shallow depth of the open water areas, and the 

possible anaerobic conditions within the wetlands.

Case bolt Wetland (PFO/PSS; Figure 24) is a small (> 0.5 acres), open water, palustrine wetland 

located 100 feet south of the Day Pond. During their survey, Gionfriddo et al. (2002) found that 

this wetland had open, shallow water; soils indicated that the wetland is permanently inundated. 

Plant species such as wild licorice, vine mesquite, pondweed, and cattails are found here. The 

source of water is likely from irrigation water overflow from an adjacent culvert or seepage from 

the Day Pond. Gionfriddo et al. noted that this wetland had experienced low water or was 

almost dry for a few years prior to their survey – probably affected by the dynamic interactions 

of the Arkansas River, alluvial aquifer and the Fort Lyons Canal. This wetland was classified by 

Gionfriddo et al. as a small pondweed (Potamogeton foliosus) type of wetland and they found a 

total of 11 wetland plant species.

The Day Wetland (PEM/OW; Figure 24) is an excavated wetland south of the fort. There is no 

hydrologic connection to the Arkansas River. Vegetation is dominated by cattails and hard stem 

bulrush with 13 wetland plant species (Gionfriddo et al. 2002).

Day Pond (PEM/OW; Figure 24) is an open water wetland just south of the fort. It was probably 

a man-made irrigation retention pond because it is deep with steep sides. Hardstem bulrush and 

cattails dominated the vegetation; Gionfriddo et al. (2002) found 15 wetland plant species. It 

was considered for removal in the late 1990’s, but was kept because of wildlife study 

opportunities and as a water source for fire suppression.

The Southwest Old Stock Tank wetland (PFO/PFL; Figure 24) is a depression that likely 

receives overflow from the Arkansas River during large flooding events. A total of 10 plant 

species was found for this wetland.

The Southeast Old Stock Tank wetland (PFO/PSS; Figure 24), is an old river channel depression 

in which a man-made stock tank was excavated circa 1940s-1950s supporting the occurrence of 

cattails; however no open water was observed (Gionfriddo et al. 2002). A total of seven wetland 

plant species was observed by Gionfriddo et al.

Natural riparian zones are some of the most diverse, dynamic, and complex biophysical habitats 

in the terrestrial environment (Naiman et al. 1993). The riparian zone encompasses that stream 

channel between low and high watermarks and that portion of the terrestrial landscape from the 

high watermark toward the uplands where vegetation may be influenced by elevated water tables 

or flooding and by the ability of the soils to hold water (Naiman and Decamps 1997). Thus, 

riparian zones may be classified as wetlands or, at the least, have a significant portion existing as 

wetland. Riparian zones are key systems for regulating aquatic-terrestrial linkages (Ward 1998) 

and they may provide early indications of environmental change (Decamps 1993).

Physically, riparian zones control mass movements of materials and channel morphology 

(Naiman and Decamps 1997). Ecologically, riparian zones: 1) provide sources of nourishment –

terrestrial inputs to rivers; 2) control nonpoint sources of pollution, in particular, sediment and 

nutrients in agricultural watersheds; and 3) create a complex of shifting habitats (both in time 
47

and space), through variations in flood duration and frequency and concomitant changes in water 

table depth and plant succession (Naiman and Decamps 1997).

The riparian zone along the Arkansas River at the NHS, prior to 2004, consisted of cottonwoods, 

with willow and tamarisk. The cottonwoods were established during the historic period when 

the river experienced periodic flooding. Stands of willow occur along the river banks and help 

delineate earlier or additional stream channels. Dense stands of tamarisk were established in the 

early part of the 20th century and in some areas overtook the native willow stands, greatly 

affecting willow regeneration. Regeneration of the cottonwoods is not naturally occurring 

because of the change in the hydrology of the river; the cottonwood stand is mature and dying 

out.

In 2004, the NHS eliminated all standing tamarisk (T. ramosissima) from the Arkansas River 

riparian area within its boundary – a total of 350 acres of tamarisk was removed. This removal 

has facilitated willow regeneration. Controlling tamarisk required cutting trees to within 6 inches 

of the ground and applying herbicide to the stumps. The NHS is assisted by the Chihuahuan 

Desert-Southern Shortgrass Prairie Exotic Plant Management Team in the continued control of 

tamarisk re-sprouting. 

Tamarisk is a facultative phreatophyte with an extensive root system that allows it to effectively 

exploit many of the degraded conditions along southwestern river systems today (e.g. interrupted 

flow regimes, reduced flooding, increased fire). Once a tamarisk stand is mature, it will remain 

the dominant feature of an ecosystem unless removed by human means. Tamarisk has a higher 

tolerance of fire, drought, and salinity than native species. It can increase fire frequency and 

intensity, drought, and salinity of a site. Hence, a strong initial infestation will promote a 

positive feedback mechanism that will lead to more tamarisk invasion (www.tamariskcoalition.org).

In 2007, a partnership formed to develop a strategic plan for Colorado’s Arkansas River riparian 

areas impacted by non-native invasive trees, principally tamarisk and Russian olive. This 

partnership, known as the Arkansas River Watershed Invasive Plants Plan (ARKWIPP) includes 

the NHS. 

The Colorado Division of Wildlife has launched a riparian mapping web page 

(http://ndis1.nrel.colostate.edu/riparian/riparian.htm). This website highlights the Division’s Colorado 

Riparian Vegetation Mapping Project, whose goal is to develop a statewide data layer of riparian 

vegetation for use in natural resource planning applications. The generation of the riparian data 

layer in the vicinity of the NHS has been completed. 

AQUATIC BIOLOGICAL RESOURCES 

Water-based Birds

There are 72 species of birds listed for the NHS in the NPSpecies database. There is relatively 

little information regarding entirely water-based bird species, and the NHS could benefit from an 

avian survey during the migratory season. Giondfriddo et al. (2002) documented the presence of 

the great blue heron (Ardea herodias), green heron (Butorides virescens), and mallard (Anas 

platyrhynchos). In a follow-up bird survey, Gionfriddo and Stevens (2003) found the following 

additional water-based bird species: black-crowned night heron (Nycticorax nycticorax); white-
48

faced ibis (Plegadis chihi); blue-winged teal (Anas discors); cinnamon teal (Anas cyanoptera); 

northern shoveler (Anas clypeata); Forster’s tern (Sterna forsteri); black tern (Chlidonias niger); 

and American Avocet (Recurvirostra americana)

Water-based Mammals

Most mammals at the NHS are primarily land-based species with two exceptions, the American 

beaver (Castor canadensis) and the common muskrat (Ondatra zibethicus). These species have 

been observed on an occasional basis (Gionfriddo et al. 2002) but little is known about current 

population size. 

Fish

Two fish surveys (Table 3) have been performed within the NHS in 2001 (Gionfriddo et al.

2002) and 2005 (Tisdale-Hein 2006). Based on these studies, 13 species of fish have been 

collected thus far in NHS waters. Gionfriddo et al. sampled via dip nets, seines and direct 

observation; however, sampling of fishes occurred only at the Day Pond and Arch Wetland. 

Because of the limited, sampling only four species of fish were collected. The only fish species 

of concern present at BEOL is the flathead chub. It is not known how abundant the flathead chub 

population is in the vicinity of the park. Tisdale-Hein collected a total of 12 species of fish; nine 

species from the Arkansas River and three species from the Arch wetland. Fish were collected 

via 15 minnow traps (10 in the river and 5 in Arch Wetland) that represented 1050 trap-hours. In 

the Arkansas River, fish were also sampled using dip netting and seines. 

It is also interesting to look at species collected by habitat. For example, Gionfriddo et al. (2002) 

found only common carp at the Day Pond. In contrast, a sampling of the Day Pond in 2005 by a 

group of science teachers found four species: red shiner; mosquitofish; green sunfish; and 

bullhead catfish (Ameriurus sp.) (Fran Pannebaker, pers. comm., Bent’s Old Fort NHS 2006). 

Similarly, Gionfriddo et al. and Tisdale-Hein (2006) each found three species at the Arch 

Wetland, but only two were in common. The two additional species, green sunfish and brook 

stickleback, represent a habitat generalist and a habitat specialist, respectively. Such differences 

in species collected from floodplain habitats are to be expected and depend on the extent of 

upstream flooding, the extent of and amount of time for local inundation, the mobility of various 

species, and sampling methodology.

The flathead chub and suckermouth minnow (Phenacobius mirabilis) are the only species of 

conservation concern (Colorado state species of concern and Colorado endangered, respectively) 

that occur within the NHS; both are resident species of the Arkansas River. It was suspected that 

the Arkansas darter (Etheostoma cragini; federal candidate species and state threatened) may be 

present in park waters. In fact, a main objective of the surveys by Gionfriddo et al. (2002) and 

Tisdale-Hein (2006) was to determine the presence of the darter. However, there is no suitable 

habitat for this darter species in NHS waters (Tisdale-Hein 2006, D. Vana-Miller, pers. obs.)

Amphibians and Reptiles

Thirteen species of reptile have been documented at the park: two turtles, spiny softshell turtle 

(Apalone spinifera) and snapping turtle (Chelydra serpentine); three lizards, Texas horned lizard 

(Phrynosoma cornutum), Great Plains skink (Eumeces obsoletus), and six-lined racerunner 
49

Table 3. Fish species collected at Bent’s Old Fort National Historic Site by three studies. The 24 species 

in the left column are from the NPSpecies database and represent those expected to be present in the 

NHS’ waters. However, NPSpecies lists 26 species – two species (red shiner and flathead chub) are 

listed twice because of taxonomic changes in genus names. The study by Nesler et al. (1999) represents 

a larger reach that includes the NHS. ‘X’ means collected.

Scientific

Name

Common

Name

Gionfriddo

et al. (2002)

TisdaleHein

(2006)

Nesler et 

al. (1999)

Dorosoma 

cepedianum

gizzard shad X

Catosmus 

catostomus

longnose sucker X

Catostomus 

commersoni

white sucker X

Campostoma 

anomalum

central 

stoneroller

X

Cyprinella 

lutrensis

red shiner X X

Cyprinus carpio common carp X X

Platygobio 

gracilis

flathead chub X X

Notropis 

stramineus

sand shiner X X

Phenacobius 

mirabilis

suckermouth 

minnow

X X

Pimephales 

promelas

fathead minnow X X

Rhinichthys 

cataractae

longnose dace

Fundulus 

zebrinus

plains killifish X X X

Gambusia 

afffinis

mosquitofish X X

Culaea 

inconstans

brook 

stickleback

X

Lepomis 

cyanellus

green sunfish X X

Lepomis humilis orangespotted 

sunfish

X

Lepomis 

macrochirus

bluegill X

Micropterus 

salmoides

largemouth bass X

Pomoxis 

annularis

white crappie X

Pomoxis 

nigromaculatus

black crappie X

Perca flavescens yellow perch X

Sander vitreus X 

Sander 

canadense

walleye X

sauger hybrid

X

Ameriurus melas black bullhead

X1 Ameiurus 

nebulosus

brown bullhead
50

Ictalurus 

punctatus

channel catfish X

1 Study noted specimens collected as Ameiurus sp. with no identification to species.

(Cnemidophorus sexlineatus); and eight snakes, bullsnake (Pituophis catenifer), plains garter 

snake (Thamnophis radix), prairie rattlesnake (Crotalus viridis), plains black-headed snake

(Tantilla nigriceps), Great Plains ratsnake (Elaphe guttata emoryi), coachwhip (Masticophis 

flagellum), western hognose snake (Heterodon nasicus), and northern water snake (Nerodia 

sipedon) (Gionfriddo et al. 2002). However, of these reptiles only the spiny softshell and 

snapping turtles are considered aquatic. Only three amphibian species have been documented: 

the Woodhouse’s toad (Bufo woodhousii), plains leopard frog (Rana blairi; Colorado State 

species of concern), and the American bullfrog (Rana catesbeiana) (Gionfriddo et al. 2002; 

Gionfriddo and Stevens 2003). Park staff have observed the presence of tiger salamanders 

(Ambystoma tigrinum), but the presence of predatory fish at the NHS wetland sites probably 

precludes successful reproduction of this species (Gionfriddo and Stevens 2003). Additionally, 

Gionfriddo et al. (2002) speculated that spadefoot toads (Scaphiopus sp. and Spea sp.) may be 

present but the timing of their survey did not coincide with the period of intense breeding activity 

for these species.

Drinking Water

Treated drinking water is supplied to the NHS via underground piping by Bent’s Fort Water 

Company (BFWC), located in La Junta, CO. BFWC has operated as many as six ground water 

wells in North La Junta. It currently operates one ground water well in North La Junta; this well 

is classified as a small public water supply, serving approximately 900 residents. The company 

purchases 50 percent of its water from the City of La Junta; when this last well fails, the 

company will purchase all of its water from the city. Over the past 10 years, BFWC has 

accrued numerous violations under the Safe Drinking Water Act for untimely monitoring of its 

wells. 

As the water from BFWC enters the NHS water room, a hypo-chlorination treatment system 

injects sodium hypochlorite solution into the source water as it flows to the storage tank. A pump 

facility takes suction from the storage tank and with the assistance of two pressure tanks, 

pressurizes a low flow reverse osmosis treatment system and the distribution system which 

supplies the buildings of the NHS. In addition, a custom bottled water treatment facility (lowflow) is operated to fill five gallon bottles for use in cooled drinking water dispensers by park 

staff.

Contaminants detected in BEOL drinking water, tested at the well source, are: barium, fluoride, 

nitrates/nitrites, copper, lead, radionuclides, sodium and total dissolved solids (TDS). 

Contaminants that exceeded the EPA maximum contaminant levels (MCL) are radium (226 and 

228 combined), and total dissolved solids in all wells. The MCL’s for TDS are secondary levels 

and are therefore non-enforceable standards set for aesthetic reasons. Elevated levels of radium 

are possibly caused by erosion and decay of natural deposits in the area. Surface and ground 

water around the NHS are known to have high levels of sodium and selenium due to irrigation 

and natural deposits in shale formations (see Hydrogeology section). 
51

Bent’s Old Fort National Historic Site is required to perform additional testing of its drinking 

and potable water, as it is considered a non-residential, non-transient water supplier. Water is 

tested the first Monday of each month, for compliance with state and federal standards. Water 

samples from the maintenance building and the fort itself are sent to the county health 

department in Pueblo, CO. Samples are tested for both types of coliform bacteria and E. coli; no 

violations have been reported. 
52
53

Water Resource Issues and Recommendations

Staff from the NHS identified the following water resource issues:

• Water rights

• High water table – impacts to the fort

• High water table monitoring wells and future monitoring

• Irrigation wells

• Fire-supply wells

• Non-potable water wells

• Drinking water

• Arkansas River water quality and quantity

• Flooding

• Hazardous substances and spill prevention

• Wetland and riparian protection – water quality and quantity

• Storm drainage issue

• Sewage treatment and septic fields

• Man-made pond and stock tanks

We have consolidated the above list in the following discussion of the water resource issues and 

our recommendations.

Water Rights and Ground Water Wells

The Bent brother’s irrigation project withdrawing water from the Arkansas River in the early 

1830’s is one of the earliest examples of appropriating water from Colorado’s streams 

(Radosevich et al. 1976). Diverting and putting water to use is considered a basic right in the 

State and that right is incorporated in the Colorado Constitution. Article XVI § 5 states: “The 

water of every natural stream, not heretofore appropriated, within the State of Colorado, is 

hereby declared to be the property of the public, and the same is dedicated to the use of the 

people of the state, subject to appropriation as hereinafter provided.” The Constitution further 

states “The right to divert the unappropriated waters of any natural stream to beneficial uses shall 

never be denied.”

Colorado follows the doctrine of prior appropriation which applies to all surface water and 

groundwater tributary to surface water. The application of this doctrine is commonly 

summarized as “first in time, first in right” whereby senior (earlier priority date) water right 

holders on a stream system have priority to use the water over junior users when there is not 

enough water to supply all users. That is, senior users may use their full entitlement before the 

next junior user may divert any water.

A water right is limited to that amount of water put to beneficial use by an appropriator. The 

Colorado Statutes state: “Beneficial use is the use of that amount of water that is reasonable and 

appropriate under reasonably efficient practices to accomplish without waste the purpose for 

which the diversion is lawfully made and without limiting the generality of the foregoing, shall 

include the impoundment of water for recreational purposes, including fishery or wildlife.” 

[Colo. Rev. Stats., §37-92-103(7)].
54

Water rights in Colorado are regulated by the Division of Water Resources; also known as the 

State Engineer’s Office. Besides administering water rights, this office issues water well 

permits, monitors stream flow and water use, performs dam safety inspections, maintains 

databases of Colorado water information, and represents Colorado in interstate water compact 

proceedings (State of Colorado, 2008).

All water matters including determination of water rights are within the jurisdiction of the State 

water courts. Each water court has jurisdiction over one of the seven major river basins in the 

State. The Arkansas River Basin is within the jurisdiction of Water Division 2.

To acquire a water right, a water user may apply for a conditional water right, which allows the 

user to work towards perfecting the right with reasonable diligence while maintaining the 

priority date of the permit application. Once the diversion works are complete and water is put 

to beneficial use, the Water Court may decree the water right as absolute.

Water use from wells can be classified as exempt or non-exempt. Exempt wells are exempt from 

water rights administration (no permitting or perfecting process required) and are not included in 

the priority system. Non-exempt wells require permits and are administered in the priority 

system.

In 1948, the States of Kansas and Colorado signed a water rights compact concerning stream

flow in the Arkansas River. The purpose of the compact is to settle disputes over flow 

entitlement and to equitably divide and apportion the waters of the Arkansas River between users 

within the two states. In the past, Kansas has not received all the water to which it was entitled 

under the compact and Kansas sued Colorado for damages. As a result, Colorado now regulates 

water use in the Arkansas River Basin very closely and no new depletions to river flow can occur 

unless the water withdrawn is replaced. New depletions and junior depletions that will cause 

Colorado to not meet its obligation to Kansas are called “out-of-priority depletions” by the State. 

The method for replacing out-of-priority depletions is documented in a Plan of Augmentation 

approved by the Water Court and often involves purchasing water from senior water right 

holders who are willing to sell or lease water (State of Colorado 2008). If the NHS requires 

additional water to meet its needs, the park will be required to have a Plan of Augmentation 

accepted by the Water Court.

The NPS, Water Resources Division, Water Rights Branch is the repository for the NPS water 

right dockets. These dockets contain relevant materials related to NPS water rights such as 

applications, permits, licenses, land transfer information, maps, water use submissions, and 

correspondence. The amount of material in each docket is variable, may contain out-of-date 

information, and some are incomplete. The following are brief summaries of the status of the 

NHS water rights found in the water right dockets:

• BEOL 001 – Point of Diversion: NW1⁄4 SW1⁄4, Sec. 14, T23S, R54W, 6th P.M. This well 

is noted as “Well No. 1” or “Federal No. 1” in the water rights dockets. An application 

for a water right permit was filed for this well in 1966 for 100 gallons per minute for fire 

protection and irrigation purposes. No other documentation exists as to whether a permit 

was granted or not. A hand-written note in the files states “Well not in use, 1987.” A 
55

June 22, 1994 memorandum from the Chief, Water Rights Branch to the BEOL 

Superintendent states (referring to Wells 1 and 2) “These wells are abandoned, no water 

right exist.”

• BEOL 002 – Point of Diversion: SE1⁄4 SW1⁄4, Sec. 14, T23S, R54W, 6th P.M. This well is 

noted as “Well No. 2” or “Federal No. 2” in the water rights dockets. A water right was 

acquired for 135 gallons per minute for fire protection and irrigation purposes from J.H. 

and Martha L. Baldridge. As stated in the Water Referee’s ruling (Case No. 80CW142, 

dated May 13, 1987), the United States withdrew any claim to water from BEOL Well 

No. 2. A June 22, 1994 memorandum from the Chief, Water Rights Branch to the NHS 

Superintendent states (referring to Wells 1 and 2) “These wells are abandoned, no water 

right exist.”

• BEOL 003 – Point of Diversion: SW1⁄4 SW1⁄4, Sec. 14, T23S, R54W, 6th P.M. This well 

is noted as “Well No. 3” or “Federal No. 3” in the water right dockets. This is an 

absolute right and consists of Permit No. 201492 for 10 gpm for drinking and sanitation 

purposes and Permit 201493 for 140 gpm for fire-fighting purpose. The priority date for 

both permits is April 1, 1965. These permits are classified as “exempt” under Colorado 

Statute 37-92-602. As a result of this classification, this well is exempt from having to 

replace out-of-priority depletions to the Arkansas River system as described in the 

Amended Rules and Regulations Governing the Division and Use of Tributary 

Groundwater in the Arkansas River Basin, Colorado, approved September 27, 1995.

• BEOL 004 – Point of Diversion: SW1⁄4 SW1⁄4, Sec. 14, T23S, R54W, 6th P.M (see Figure 

24). This well is noted as “Irrigation Well” or “Federal No. 4” in the water right dockets

and the “Day Well” by the NHS staff. This is an absolute underground right for 720 gpm 

(not to exceed 153 acre-feet per year) for irrigation purposes with a priority date of 

January 30, 1954. A 1995 document shows that the NHS transmitted monthly electric 

meter readings (from November, 1994 through October, 1995) and the total volume of 

water pumped to the State for this well. The 1974 Water Referee’s ruling (W-3016) 

states the well number is RF-653, a replacement for 013596-F. No permits are found in 

the water rights dockets. 

In the mid-1990s, the NHS proposed a project to revegetate certain lands (the old Day 

property) with native vegetation. Since they wanted to use water from this well, a plan of 

Augmentation was required to replace the out-of-priority depletion to the Arkansas River 

system as described in the Amended Rules and regulations Governing the Division and 

Use of Tributary Groundwater in the Arkansas River Basin, Colorado, approved 

September 27, 1995.

The NHS eventually contracted with the Colorado Water Protective and Development 

Association who in turn supplied water to the river to augment the park’s out-of-priority 

depletion from their approved Augmentation Plan. In 1997, the NHS used 160 acre-feet 

per year (afy) to irrigate 40 acres, but reduced that amount to 20 afy in approximately 

2000. The park ceased using this water after 2009 (Fran Pannebaker, Bent’s Old Fort 

NHS, pers. comm., September 2008).
56

• BEOL 005 – Point of Diversion: SE1⁄4 SE1⁄4, Sec. 23, T23S, R54W, 6th P.M. This well is 

noted as “Livestock Well” in the water right dockets. A well abandonment affidavit 

states the well was plugged and abandoned on December 13, 1989.

• BEOL 006 - Point of Diversion: SE1⁄4 NE1⁄4, Sec. 23, T23S, R54W, 6th P.M (see Figure 

24). This well is noted as “Harmon Property” in the water right dockets. Well 

Registration No. 156062-A was issued on December 13, 1989 for this well. A Notice of 

Inactive Well form, which was likely submitted to the Division Engineer, is found in the 

docket stating the well was disconnected from its power supply. The notice is signed by 

the BEOL Superintendent on June 13, 1995. It is an exempt well as classified by the 

State of Colorado. As a result of this classification, this well is exempt from having to 

replace out-of-priority depletions to the Arkansas River system as described in the

Amended Rules and regulations governing the Division and Use of Tributary 

Groundwater in the Arkansas River Basin, Colorado, approved September 27, 1995.

The NHS is interested in restoring approximately 100 acres of land south of the Arkansas 

River to native vegetation. Recently, it was suggested that the park request the CWPDA 

to transfer the 20 afy associated with BEOL 004 to BEOL 006 for the purposes of

irrigating this land during the restoration process (Hughes 2010). 

The NHS has the rights to 47 shares in the Fort Lyons Canal Company acquired from Barbara 

Day and Robert and Evelyn Wilburn for irrigation purposes. These shares equate to 0.47 cubic 

feet per second of water from the Company. Park staff state that the park has never used this

water (Fran Pannebaker, Bent’s Old Fort NHS, pers. comm. September 2008). Hughes (2010) 

mentioned that a possible near-term use of these shares could be for irrigation of the native 

vegetation restoration on NHS lands south of the Arkansas River. In this case the NHS could 

offer the CWPDA all or part of its 47 shares; the CWPDA would then evaluate the shares and 

determine the amount of ground water that the shares represent. This ground water could then be 

pumped from one of the existing wells for irrigation purposes.

Recommendations

The water rights information described above should be updated to fill in missing information as 

to the history and present status of NHS water rights for both the park files and Water Rights 

Branch dockets. In order to accomplish this task, files from the Colorado Division of Water 

Resources, Fort Lyon Canal Company, and the Colorado Water Court should be reviewed and 

copies made of missing information for each well and ditch right. Submitting a Technical 

Assistance request to the NPS, Water Resources Division is an option if NHS does not have the 

staff or expertise in this matter. Also, an analysis should be made by the park as to its current 

and future water needs to determine if existing NHS water rights are adequate. If certain wells 

and/or water rights are no longer needed, an effort to properly abandon the well(s) and right(s) 

should be undertaken. Since more irrigation use is planned for other areas of the NHS, an effort 

should be made to see if the NHS shares in the Fort Lyons Canal Company could be exchanged 

for the right to divert tributary ground water from the Arkansas River basin.
57

Water Quality and Quantity of the Arkansas River

Two of the three water-based vital signs of the SOPN are surface water quality and quantity. 

Texas State University (2007), working for the SOPN, reviewed available surface water 

information in network parks and provided the following recommendations for the NHS:

• Water quality data collected since the early 1990s should be compiled, incorporated into 

the historical database, and analyzed for water quality condition and trends, particularly 

for U.S. Geological Survey gaging station on the Arkansas River at Hadley, CO (USGS 

#07123300) commonly referred to as station BEOL 7 (see NPS 1998);

• Routine (weekly) water quality monitoring of vital sign core constituents (water 

temperature, dissolved oxygen, pH, specific conductance and indicator bacteria) should 

be conducted at BEOL 7. This should be supplemented by seasonal, continuous (diel) 

monitoring of DO and pH to provide additional understanding of river chemical 

conditions. Consideration should also be given to monthly monitoring of nutrient 

concentrations and major ions (e.g., sulfate and total dissolved solids);

• Annual or seasonal monitoring of aquatic biological condition (primarily 

macroinvertebrates) because aquatic biota integrate water quality conditions over time.

Recommendations

NPS (1998) provided a basic retrospective analysis of water quality conditions at those 

monitoring stations with records in STORET, the national water quality database. In our 

estimation that analysis was and is of limited value to the NHS, simply because the closest 

upstream station with an adequate period of record is in La Junta, 8 miles west of the NHS. The 

closest downstream station is on the Arkansas River at Hadley, CO (USGS #07123300 and 

BEOL 7), two miles downstream. However, that station has been inactive since the 1980’s and 

has a very limited period of record that did not measure discharge. This station would not be 

viable for any retrospective water quality analysis, let alone any current monitoring. The La 

Junta station (USGS #07123000) has an adequate period of record (in some cases > 50 years and 

current) for most of the five core water quality vital signs. Additionally, other important 

constituents (e.g. calcium, sulfate, selenium) also have adequate periods of record. Most 

importantly, discharge is measured at this station. Because there are no permanent water inputs 

to the Arkansas River between La Junta and the NHS, the analysis of water quality data from the 

La Junta station would provide useful information. We recommend that the NHS submit a 

technical assistance request to the NPS Water Resources Division for a status and trends analysis 

of water quality and discharge information for the La Junta station. 

Similarly, the establishment of any routine water quality monitoring at the Hadley station would 

also be problematic. We recommend two options for the establishment of routine water quality 

monitoring of the Arkansas River at the NHS. First, the SOPN could establish a core vital signs 

monitoring site just downstream of the west boundary of the NHS; a quarterly sampling

frequency would be the minimum. These water quality data could be correlated with the 

discharge data of the La Junta station. Additionally, the network could data mine the La Junta 

site for other important constituents. Second, the network or NHS could totally rely on data 

mining of discharge and water quality data from the La Junta station.
58

Routine monitoring of biological condition is an important tool in understanding overall water 

resource condition. Because the sampling, identification, and analysis of the aquatic 

macroinvertebrate community require specialized expertise, we do not recommend this as 

something to be accomplished by the NHS. The SOPN would be the NPS entity better suited for 

the lead in such an assessment; however, understanding aquatic biological condition is not a 

SOPN vital sign, and may be of low priority.

Colorado’s Ecological Monitoring and Assessment Program (EMAP) within the Colorado 

Department of Public Health and the Environment developed bioassessment tools for use in 

monitoring and assessing streams statewide. Specifically, that program developed a benthic 

macroinvertebrate multimetric index for streams and rivers in the plains region of Colorado 

(CDPHE No Date; www.cdphe.state.co.us/wq/WaterShed/ColoradoEMAPReport.pdf). Multimetric indices

(MMI) allow multiple biological measurements or metrics to be combined into a single unitless 

index value. Metrics are attributes of the biological assemblage, which can be quantified as a 

response to human and natural alteration or stress of the environment. MMIs are calibrated using 

reference conditions. By incorporating metrics representing species richness, species 

composition, functional feeding group, and pollution tolerance of benthic communities, MMIs 

can accurately indicate macroinvertebrate community health. The metrics involved in this index 

and the associated ecological categories are:

 Metric Category

Percent Chironomidae Composition

EPT Taxa Richness

Hilsenhoff Biotic Index Tolerance

Percent Burrowers Habit

Percent Predators Trophic

In addition, a fish-based MMI was developed for Colorado plains rivers and streams (CDPHE no 

date) that included the following metrics:

 Metric

Number of nonnative individuals

Percent of species that are native herbivores

Percent of hider individuals

Percent of native species that are long-lived and tolerant to sediment

Percent of native individuals that prefer warm-water habitats

 Number of individuals that are benthic and tolerant to sediment

Paul et al. (2005) recommended that the State of Colorado implement the use of these MMIs to 

assess biological condition in streams and rivers of the plains. To our knowledge the State has 

not done so. One reason may be that these plains MMIs were constructed with very few 

reference (n=6) and stressed (n=3) sites. As a result, little of the true natural variation in metric 

values was characterized. Thus, their applicability is limited until verified with an independent 

set of data or recalibrated with larger sample sizes.
59

We recommend that the NHS contact the Colorado Department of Public Health and the 

Environment and propose that the State sample the Arkansas River macroinvertebrate 

community within the boundaries of the NHS as an additional stressed site. This would be a 

limited assessment to assist the State with refining the plains MMI. For the long-term, perhaps 

the NHS and State could develop a Memorandum of Agreement for the State to monitor the 

macroinvertebrate community in the Arkansas River at the NHS using the plains MMI on a 

recurring basis as part of a statewide assessment of stream biological condition. The same could 

be said for the fish-based MMI.

High Water Table and Impacts to the Bent’s Old Fort

The study by Woods et al. (2002), although limited in scope and duration, provided the likely 

scientific basis for flooding of the Fort’s basement. They believed that the primary control on 

ground water levels in the area around the NHS is the ground water flow from adjacent uplands, 

and the amount of this flow is dependent on the amount of excess irrigation and leakage from the 

Fort Lyon Canal. Under low to average flow conditions in the Arkansas River, the ground water 

gradient towards the river is maintained – the river reach through the NHS is maintained as a 

gaining reach. Under high flow conditions in the Arkansas River, a local reversal of the

hydraulic gradient can occur such that ground water flows away from the river (and towards the 

Fort) and the river reach through the NHS is now a losing reach. They observed that the 

basement flooding in 1999 was associated with a peak flow in the Arkansas River that was twice

as large as the second largest peak flow recorded since closure of the Pueblo Dam in 1974. The 

river stage in 1999 was more than 2.1 m higher than the peak flow in 2001 (year of study). Such 

high flows in Arkansas River could lead to a reversal in the hydraulic gradient. Woods et al.

concluded that the flow of water from the river combined with increased leakage from the canal 

were the likely cause of the high water table levels and subsequent basement flooding in the fort. 

Additionally, high river stage may only reduce the overall groundwater gradient and hamper

drainage of water seeping from the Fort Lyon Canal (Woods et al. 2002). In particular, water 

flooding the basement may indeed be coming from the canal rather than the Arkansas River, but 

the net result is the same. Woods et al. believed that a more detailed term study of different water 

sources and aquifer properties would be needed to evaluate the effect of the river, the canal and 

excess irrigation on water table elevations and basement flooding at the Fort.

Recommendations

Given that ground water quantity is a vital sign of the SOPN, we agree with the 

recommendations by Texas State University (2007), namely:

• Historic and future (see below) ground water elevation data should be consolidated 

within an electronic database and coordinated with the operation of an appropriate 

national or state-related database, and

• Given the connection between periodically high water tables and flooding of the Fort, the 

NHS should renovate at least a select few of the PVC-lined, hand augured and well-point 

driven piezometers installed by Woods et al. (2002) (Figure 25) and renew efforts to 

monitor ground water elevations.
60

Figure 25. Locations of ground water monitoring wells (1-4,6; 8-15; 18-19) and wetland staff gages (5 

and 16) and Arkansas River staff gages (7 and 17) from the study by Woods et al. (2002).

With regard to the first recommendation, we suggest that the NHS submit a technical assistance 

request to the NPS Water Resources Division for assistance with the database and any 

integration with national/state databases.

With regard to the second recommendation, we suggest the renovation of wells 1, 2 and 3 

because of their close association with the Fort and lack of correlation with river stage (see 

Woods et al. 2002) and wells 8 and 11 due to their floodplain location and relatively strong 

correlation with Arkansas River stage (Figure 25) (see Woods et al.). Water table elevations in 

these wells should be monitored monthly and linked with monthly-monitored levels at the 

Arkansas River staff gages (sites 7 and 17 in Figure 25) and other appropriate benchmarks (see 

Woods et al. 2002). This will link river stage levels with hydraulic head. 

For the present, we do not agree with Woods et al. (2002) that a more detailed term study of 

different water sources and aquifer properties is needed to parse out of the relative effects of 
61

river, canal and excess irrigation on water table levels and basement flooding at the fort. Such 

knowledge, while of heuristic value, would do little in terms of improving of knowledge and 

mitigating the flooding problem. That basement flooding of the Fort is caused by a combination 

of high river stage and canal seepage/excess irrigation is of high scientific probability based on 

the study by Woods et al. (2002). Therefore, barring the improbable -- moving the location of 

the Fort, the NHS should center its energy on mitigation and remediation of the Fort basement, 

although the available methods are limited. In addition, the NHS should work with such local 

entities as the Southeast Colorado Resource Conservation and Development Council to 

understand (hence the need for a renewed effort to monitor ground water levels) and mitigate the

amount of excess irrigation and canal leakage flowing towards the NHS. In the future, a study 

similar to the one proposed by Woods et al. may become necessary; if so, the NHS should 

request technical assistance from NPS Water Resources Division in the development of the 

project.

Wetland and Riparian Protection

The Arch wetland has increased in size from a saltgrass meadow in the 1980s to a 57-acre 

wetland in the 1990s apparently in response to the local rise in water table elevation. Woods et 

al. (2002) determined that the primary water source for this wetland is ground water from 

adjacent uplands. This means that decreasing flow in the Fort Lyon Canal could cause a decrease 

in the size of the Arch wetland. Similarly, an increase in ground water withdrawals up gradient 

from the wetland could reduce ground water inflows and reduce the size of the wetland.

The NHS is seeking advice with regard to protection and use of its artificial wetlands, namely, 

the Day Pond, Day Wetland, and the SW and SE Stock Tanks. Under Procedural Manual #77-1

(NPS 2008; see page 10), man-made tanks and ponds are considered artificial wetlands. 

Previously, Noon et al. (2005) advised against the suggestion by the County Health Department 

that the stock tank wetlands be filled to eliminate mosquito breeding and the spread of West Nile 

virus, unless there were compelling reasons. However, the reasons were not compelling since 

these artificial wetlands may replace wetland functions that historically occurred along the 

Arkansas River floodplain, but may have been filled in for agricultural development; filling them 

would produce a net loss of wetlands and there would be significant costs for environmental 

compliance and any earthmoving/re-vegetation operations. Any filling of the stock tank 

wetlands or the Day Pond and Day Wetland, would also have an adverse impact on those 

wetlands and would require full NEPA compliance (i.e., an environmental assessment or 

environmental impact statement) and, in most cases, preparation of a wetland statement of 

findings (SOF). The SOF, attached to the environmental compliance document, documents 

compliance with NPS wetland policies and procedures (see page 10).

The maintenance of healthy riparian systems is essential in obtaining and sustaining biologically 

diverse ecosystems. Healthy riparian systems are geologically stable, with stream flow and 

sediment discharges in dynamic equilibrium with their upland watersheds. The systems’ wetland 

and riparian vegetation has appropriate structural, age, and species diversity. When these 

attributes are maintained, riparian systems provide forage and cover for wildlife and improve 

water quality by filtering sediment and recycling nutrients. If, however, any of the essential 

attributes are missing or degraded, or if the system becomes geologically unstable, widespread 
62

erosion many occur that will degrade water quality and cause damage or loss of wetland and 

riparian habitats. 

Texas State University (2007) recommended that bank stabilization could be better understood 

and quantified by stream and riparian assessments of habitat condition. A riparian assessment 

tool, The Process for Assessing Proper Functioning Condition (Pritchard et al. 1998), has been 

used in the western U.S. to evaluate riparian systems by the U.S. Bureau of Land Management. 

This technique uses an interdisciplinary team to assess riparian area “functionality” according to 

17 hydrologic, vegetation, and stream geomorphologic factors such as erosion, deposition, and 

channel geometry. It provides an initial screening that can separate areas that are functioning 

well from those in need of more intensive evaluation or management actions. 

Evaluation of the functioning condition is not simply an assessment of the ecological status or 

serial stage of the vegetation community. Rather, evaluation is based upon the concept that the 

basic elements of physical habitat must first be in place and functioning properly before

management of such things as potential natural vegetation communities can occur. 

The basic goal of this process is to classify streams as “proper functioning”, “functional at-risk”, 

or “nonfunctional.” To do this, the interdisciplinary team evaluates existing literature and 

conducts field examinations to obtain information that includes the following:

• Identification and description of relic areas;

• Review of historical photos, survey notes, and other documents that indicate historic 

condition;

• Review of floral and faunal lists;

• Determination of species habitat needs related to species that are or were present;

• Estimation of the frequency and duration of flooding on floodplain and terraces;

• Identification of current vegetation and determination of historical occurrence in the area;

• Determination of entire watershed’s general condition and identification of its major 

landforms; and,

• Identification of limiting factors, both human-induced and natural, and determination of 

needed remedial actions.

Recommendations

Because the NHS expressed concern about the quality of its wetlands, Texas State University 

(2007) suggested periodic monitoring of aquatic plants and animals similar to the approach by 

Gionfriddo et al. (2002). We concur with that suggestion and recommend a recurrence interval 

of every five years. Additionally, we recommend monitoring for a suite of water quality 

parameters similar to those measured by Woods et al. (2002) in the NHS wetlands and would 

specifically include pH, temperature, dissolved oxygen, specific conductance, nitrogen 

(dissolved ammonia, total ammonia + organic, dissolved nitrate and nitrite, and dissolved nitrite),

and phosphorus (dissolved and ortho-phosphorus dissolved). Sampling locations should be 

fixed; in the case of the Arch and Casebolt wetlands, sampling should occur at the previous well 

monitoring sites for those wetlands (see Figure 25). Sampling frequency, initially, should be 

quarterly, and depending upon the analysis of data for a three to five year timeframe, sampling 

could occur annually (summer). Additionally, we recommend the establishment of a monitoring 
63

station on the Arch Wetland that is down gradient from the septic system at the Fort – this site 

should be monitored at least quarterly for nitrogen and phosphorus constituents (see discussion 

under Sewage Treatment and Septic Systems below). 

We agree with Texas State University (2007) in recommending the renovation of the monitoring 

wells established in the Arch and Casebolt wetlands by Woods et al. (2002) (wells number 16 

and 5, respectively in Figure 25). Ground water elevations should be recorded on a monthly 

basis and linked with levels at the Arkansas River staff gages (sites 7 and 17 in Figure 25), other 

ground water monitoring wells, and other appropriate benchmarks (see Woods et al. 2002) so 

that that all sites can be associated with hydraulic head and stream stage (see discussion under 

High Water Table and Impacts to Bent’s Old Fort).

We recommend that the artificial wetlands (Day Pond, Day Wetland, and stock tank wetlands) be 

managed for their wetland functions, which include floodwater storage/attenuation, ground water 

recharge, amphibian breeding habitat, and other wildlife habitat.

It is recommended that the NHS submit a technical assistance request to the NPS Water 

Resources Division for an assessment of the riparian conditions along the Arkansas River using 

The Process for Assessing Proper Functioning Condition (Pritchard et al. 1998). It is also 

recommended that the recurrence interval for additional assessments be every five years.

Additionally, the NHS should establish GPS-based photograph points on the banks of the 

Arkansas River. Photographic monitoring (digitally based) is a simple and inexpensive method 

to assess changes in stream geomorphology (especially changes since tamarisk removal), the 

riparian zone, and other physical habitat features that may be associated with site and watershed 

conditions. A series of photographs would also allow detection of slow, progressive changes in 

physical habitat features that otherwise might go undetected until the accumulation of impacts is 

noticeable. 

Initially, three photo points should be established: 1) west boundary of NHS looking down river; 

2) east boundary of NHS looking up river; and 3) at a point approximately 1.1 miles from either 

boundary (midpoint of river miles in NHS) and looking both up and down river. Photographs 

should be taken during the following times each year: 1) baseflow conditions (Figure 13, 

December-February; 2) ascending limb of hydrograph (Figure 13, May-June); and 3) descending 

limb of hydrograph (Figure 13, July-September).

Flooding and Stormwater Drainage 

Storm drainage around the NHS employee entrance road to the maintenance yard and 

administration building is a problem during most heavy rain events (Figure 26). A drainage 

ditch runs along the west side of the road. The ditch has culverts under two access roads to the 

maintenance yard and one to the administration building. The ditch catches runoff from the 

surrounding area west of the entry road. 

Storm water collects in the ditch at the top (north) end next to the maintenance building and 

extends south below the cattle guard crossing for the administration building (total length of 

approximately 300 ft). The ditch essentially acts as a 300-foot-long, linear retention basin with
64

Figure 26. View of the park employee entrance gate as it passes along the maintenance and 

administration buildings. The flooding ditch is parallel to the road and between the road and buildings.

no defined outfall. When the ditch is full, excess water likely overflows the high point further 

south along the edge of the road and continues south toward the river. However, there is no clear 

channel to indicate where the overflow goes. 

Recommendations

One possible solution to the drainage problem is to design an outfall at the south end of the ditch. 

A ditch and/or culvert extension should be placed to allow positive drainage from the south end 

of the existing ditch to an area that is lower in elevation. It appears from field observations that 

one option is to run a culvert to the southeast under the entry road that would day light at a lower

elevation in the open field. Since the area seems relatively flat, the culvert may have to be quite 

long in order to meet grade at a lower elevation in the field. The low areas in the field have 

water lines and sewer pump station pipes that may or may not allow deposition of sheet flow 

from the ditch. Another option is to continue the ditch and culverts to the south along the entry 

road. However, this would end up contributing to the existing drainage system that is further 

south, which serves the parking lot for the visitor center, and the additional flow may overload 

that system. The following tasks need to be completed in order to identify, select, and 

implement the best solution:

o Complete a detailed topographic survey (no more than one-foot contour elevations) of the 

entire drainage ditch including culvert inverts, and the survey should also include the area 

at least 100 feet on either side of the existing ditch, the area around the southern end of 

the ditch including the road south to the visitor center parking lot, and the open field area 

(for several hundred feet east of the entry road). Also the water lines, pump station, and 

sewer pipes that run through the field on the east side of the entry road should be 

surveyed.

o Analyze the topography to determine the best solution. Consider the length of culvert 

necessary depending on the amount of drop in elevation needed to move the water, 

clogging and maintenance problems, potential erosion problems, and impacts to other 

infrastructure. Also consider other options including detention basin(s).
65

o Replace all of the culverts in, and dredge, the existing ditch. Since the culvert is acting 

like a detention basin, the sediment laden water collects in the ditch, slows down, and 

deposits sediment such that the culverts are half-buried and the ditch is filling with silt. 

Sewage Treatment and Septic Systems

There are two septic systems at the NHS: 1) a 1,000-gallon septic tank located west of the visitor 

parking lot, circa 2000; and 2) a 5,000-gallon septic tank located just west of the fort corral, circa 

1970s. The NHS has these septic tanks pumped every three to five years. The smaller, younger

septic tank is located on the upper terrace level, outside of the 500-year floodplain, and not 

adjacent to any water resources. As long as this septic tank is properly maintained we do not 

expect any leaching of nutrients into down slope water resources, such as the Arch Wetland. 

However, the larger, older tank is located within the 500-year floodplain and adjacent to wetland 

and riparian resources. Given the age of this septic tank and its proximity to water resources, 

nutrients (primarily nitrogen and phosphorus) may become a water quality problem for the Arch 

Wetland.

Recommendations

We recommend the monitoring of nitrogen and phosphorus as part of a monitoring program for 

the Arch Wetland (see discussion under the Wetland and Riparian Protection issue, above).

Hazardous Waste Management and Spill Contingency Planning

For most of the NPS units like the NHS, internal NPS operations require that hazardous 

substances, such as petroleum products used in maintenance operations, be stored and handled 

on a routine basis. Although it is the goal of the NPS to minimize releases of these substances 

into the environment, accidental releases still occur. The action of those employees who first 

encounter contamination in the NHS could well determine the severity of the impact(s) on 

human health and the environment. Therefore, it is important for NPS staff to understand the 

basic requirements for response to hazardous substance spills.

An even greater concern for hazardous spills in the NHS exists from external operations. The 

corridors for State Route 194 and the railroad run parallel to the NHS, to the north and south, 

respectively (see Figure 1). Trucks and trains carry fuel oil, diesel fuel, gasoline, and a variety of 

agricultural and industrial chemicals along these corridors. 

Given these potential pollution pathways, an accidental release of hazardous materials is a 

continuous threat to the NHS’s natural resources. The NPS is severely limited in qualified 

personnel, spill response equipment, and baseline natural resource information to effectively 

respond to and evaluate impacts from hazardous spills to the NHS. Emergency response to a 

major spill requires expertise and field equipment that extends beyond the capabilities of the 

NPS. In accordance with the National Contingency Plan established under the Clean Water Act, 

federal agencies are required to have a Spill Contingency Plan (SCP) for emergency response to 

any spill of oil or hazardous substances for which they are responsible. Furthermore, a Spill 

Prevention Control and Countermeasure Plan (SPCCP) is required for the NPS to maintain 

compliance with 40 CFR 112 (EPA Regulations on Oil Pollution Prevention). 

At the NHS, petroleum product use is focused around the maintenance yard. There are two 

above ground petroleum storage tanks in service at the NHS, one for diesel and one for unleaded 
66

gasoline. The maintenance facility also stores numerous small containers of paints, hydraulic 

fluids, motor oil, and gasoline. The NHS has not completed an Oil Spill Prevention and 

Response Plan.

An environmental compliance audit has completed for the NHS as part of a sevicewide program 

that requires all NPS facilities to receive an environmental audit. Only one of 11 

findings/recommendations is important with regard to water resources – the need for a current 

hazardous chemical inventory.

The Resource Conservation and Recovery Act (RCRA), as amended by the Hazardous and Solid 

Waste Act Amendments of 1984 and Title III of the Superfund Amendment Reauthorization Act 

(SARA Title III) require hazardous waste reduction programs. Executive Order 12873 

establishes the goal for federal agencies to reduce their input into the waste stream by 40 percent. 

Recommendations

The NHS should strongly consider developing an Oil Spill Prevention and Response Plan. Such 

a plan would present site-specific information on those locations in the NHS that have the 

potential to experience such environmental change. In addition, general structural and 

operational recommendations would be outlined to prevent spills associated with all on-site 

activities involving the storage and/or use of petroleum products or other hazardous materials. A 

notification sequence, including emergency contacts, would be provided if a spill occurs. The 

Plan would be intended for use by all personnel responsible for storage, handling, and removal of 

hazardous substances at the NHS.

The NHS should implement or improve waste reduction programs through recycling efforts that 

are applicable to both park staff and visitors.
67

Water Resources of Bent’s Old Fort National Historic Site 

and Climate Change

Over the past 50 years, Colorado has experienced rising temperatures, increased precipitation, 

and altered surface water flow due to climate change. The State’s eastern plains are experiencing 

higher temperatures; however, temperature in the Arkansas River Valley has increased by only 

0.5o F (U.S. EPA 1997, U.S. Global Change Research Program 2000). Over the next century 

Colorado is likely to see higher temperatures and more precipitation in some regions while water 

resources are likely to become less secure (U.S. EPA 1997). Changes in the water cycle will be 

the vehicle for many impacts of climate change (www.colorado.edu/CO_Climate_Report/index.html).

The Intergovernmental Panel on Climate Change (2007) determined that seasonal temperature 

changes and overall increased precipitation (Regonda et al. 2005), less of which is falling as 

snow, have led to less snow pack and earlier spring thaw on average in the Rocky Mountains. 

Between 1978 and 2004, the spring runoff has shifted earlier by two weeks 

(www.colorado.edu/CO_Climate_Report/index.html). In the future, winter precipitation could increase 

by 20 to 70 percent, with high altitudes receiving the largest amount (U.S. EPA 1997). This 

could alter the seasonal flow patterns of major rivers that originate in the Rocky Mountains, 

intensifying summer droughts in downstream areas as late-summer flows become reduced (IPCC 

2007). The change in weather patterns caused by warmer temperatures is expected to increase 

the risk of drought.

Given observed trends in regional warming and declining snowpack conditions, studies have 

been conducted to relate potential future climate scenarios to runoff and water resource

management impacts. Elgaali et al. (2007) and Ojima et al. (1999) reported potential climate 

change impacts on water resources and demands in the Great Plains. Changes in agricultural 

water demands were evaluated based on climate change scenarios using crop consumptive use 

methods. Both studies project future increases in crop water consumptive use ranging from 20 to 

60 percent by the end of the 21st century. 

Based on recent scenario studies, it appears that warming without precipitation change would 

trigger a seasonal shift toward increased runoff during the winter and decreased runoff during the 

summer. On the other hand, it also is plausible (based on climate projections) that precipitation 

increase could occur with regional warming and offset a significant portion of summer runoff 

decreases associated with warming alone. Garbrecht et al. (2004) suggested that the fall through 

spring months would be most impacted by either a wetter or drier Great Plains climate with 

stream flow experiencing the greatest impact.

Reduced mountain snowpack, earlier snowmelt, and reductions in spring and summer stream 

flow volumes originating from snowmelt likely would affect surface water supplies and could 

trigger heavier reliance on ground water resources (Ryan et al. 2008). Also, if a larger 

percentage of annual precipitation is in the form of intense rain events with high runoff, 

infiltration and aquifer recharge could be reduced. However, warmer wetter winters could 

increase the amount of water available for ground water recharge.
68

Whether water quality conditions improve or decline under climate change depends on several 

variables including water temperature, flow, runoff rate and timing, and the physical 

characteristics of the watershed. Climate change has the potential to affect all of these variables. 

Climate change impacts on surface water systems very likely will affect their capacity to remove 

pollutants and improve water quality; however, the timing, magnitude, and consequences of 

these impacts are not well understood (Lettenmaier et al. 2008). 

Covich et al. (1997) predicted Great Plains region impacts on aquatic ecosystems based on two 

climate change scenarios. Predicted aquatic ecosystem impacts were based primarily on changes 

in water temperatures, nutrients, and food sources. For example, increased summer air 

temperatures could increase dry season aquatic temperatures and affect fisheries habitat. The 

confidence in their predictions for aquatic impacts is higher for the southern Great Plains area, 

including the NHS. 

We recommend that the NHS submit a technical assistance request to the NPS Climate Change 

Response Program for the application of the Climate Change Scenario Planning process to 

explore potential futures at the NHS based on the most recent science. 
69

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