DOE-ID-11263 

January 2006 

Feasibility Assessment of the Water Energy 

Resources of the United States for 

New Low Power and Small Hydro Classes of 

Hydroelectric Plants
 

U.S. Department of Energy 

Energy Efficiency and Renewable Energy 

Wind and Hydropower Technologies 
 

 

 

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To learn more, visit http://www.eere.energy.gov/ 

NOTICE 

The information in this report is as accurate as possible within the limitations of the uncertainties of the basic data 

and methods used. The power potential quantities presented in the report were determined analytically. Document 

users need to ensure that the information in this report is adequate for their intended use. Battelle Energy Alliance, 

LLC makes no representation or warranty, expressed or implied, as to the completeness, accuracy, or usability of 

the data or information contained in this report. 

The term “available” as used to refer to water energy resource sites or a category of power potential in this report 

denotes only that sites and their corresponding power potential are not located in a zone where hydropower 

development is unlikely and do not correspond to the location of an existing hydroelectric plant. The term does not 

denote any knowledge of the feasibility of developing or of any resource owner or agency having jurisdiction over a 

resource having an interest in developing or intent to develop any resource for the purpose of hydroelectric 

generation. 

The term “feasible” as used to refer to water energy resource sites or a category of power potential in this report 

denotes only that sites and their corresponding power potential have met a limited set of feasibility criteria and been 

so designated via the methodology described in the report. Actual feasibility of a site for development as a 

hydroelectric plant must be determined by a site specific, comprehensive evaluation performed by the perspective 

developer. 

DISCLAIMER 

This information was prepared as an account of work sponsored by an agency of the U.S. 

Government. Neither the U.S. Government nor any agency thereof, nor any of their employees, 

makes any warranty, express or implied, or assumes any legal liability or responsibility for the 

accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, 

or represents that its use would not infringe privately owned rights. References herein to any specific 

commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, 

does not necessarily constitute or imply its endorsement, recommendation, or favoring by the U.S. 

Government or any agency thereof. The views and opinions of authors expressed herein do not 

necessarily state or reflect those of the U.S. Government or any agency thereof. 
DOE-ID-11263
 

Feasibility Assessment of the Water Energy 

Resources of the United States for 

New Low Power and Small Hydro Classes of 

Hydroelectric Plants 

Douglas G. Hall, INL 

Kelly S. Reeves, NPS 

Julie Brizzee, INL 

Randy D. Lee, INL 

Gregory R. Carroll, BNI 

Garold L. Sommers, INL, retired 

IDAHO NATIONAL LABORATORY 

Published January 2006 

Prepared for the 

U.S. Department of Energy

Office of Energy Efficiency and Renewable Energy

Wind and Hydropower Technologies Program

Idaho Operations Office 

ABSTRACT 

Water energy resource sites identified in the resource assessment study 

reported in Water Energy Resources of the United States with Emphasis on Low 

Head/Low Power Resources, DOE/ID-11111, April 2004 were evaluated to 

identify which could feasibly be developed using a set of feasibility criteria. The 

gross power potential of the sites estimated in the previous study was refined to 

determine the realistic hydropower potential of the sites using a set of 

development criteria assuming they are developed as low power (less than 

1 MWa) or small hydro (between 1 and 30 MWa) projects. The methodologies 

for performing the feasibility assessment and estimating hydropower potential 

are described. The results for the country in terms of the number of feasible sites, 

their total gross power potential, and their total hydropower potential are 

presented. The spatial distribution of the feasible potential projects is presented 

on maps of the conterminous U.S. and Alaska and Hawaii. Results summaries for 

each of the 50 states are presented in an appendix. The results of the study are 

also viewable using a Virtual Hydropower Prospector geographic information 

system application accessible on the Internet at: 

http://hydropower.inl.gov/prospector. 

iii 
iv 
SUMMARY 

The U.S. Department of Energy (DOE) has an ongoing interest in 

assessing the water energy resources of the United States. Previous assessments 

have focused on potential projects having a capacity of 1 MW and above. These 

assessments were also based on previously identified sites with a recognized, 

although varying, level of development potential. 

The Idaho National Laboratory with the assistance of the U.S. Geological 

Survey completed water energy resource assessments of all 20 hydrologic 

regions in the United States in 2004 (reported in Water Energy Resources of the 

United States with Emphasis on Low Head/Low Power Resources, 

DOE/ID-11111, April 2004). In combination these results produced an 

assessment of the gross power potential of every natural stream in the United 

States. Parsing of the regional assessment results using geographic information 

system (GIS) tools produced assessment results for each of the 50 states. 

In the present study, the water energy resource sites that were identified in 

the prior study were evaluated to determine the feasibility of their development 

using a set of feasibility criteria. These criteria considered site accessibility, load 

or transmission proximity, and land use or environmental sensitivities that would 

make development unlikely. Water energy resource sites that met the feasibility 

criteria were designated as feasible potential project sites. More realistic 

estimates of the power potential of these sites were determined by assuming a 

development model not requiring a dam obstructing the watercourse or the 

formation of a reservoir. The development model included a penstock running 

parallel to the stream, culminating in a powerhouse whose tailwater returned the 

working flow to the stream. It was assumed that only a low power (<1 MWa) or 

small hydro (≥1 MWa and ≤30 MWa) plant would be installed at the site. The 

working flow was restricted to half the stream flow rate at the site or sufficient 

flow to produce 30 MWa, whichever was less. Penstock lengths were limited by 

the lengths of penstocks of a majority of existing low power or small 

hydroelectric plants in the region. A methodology was employed to determine the 

optimum penstock length and location on the stream reach corresponding to the 

site based on yielding the maximum hydraulic head with the minimum length. 

The population of water energy resource sites that was assessed was 

composed of slightly over 500,000 sites having a collective, gross power 

potential of slightly less than 300,000 MWa. The feasibility assessment identified 

approximately 130,000 sites meeting the feasibility criteria. These sites have a 

total gross power potential of nearly 100,000 MWa. Application of the 

development model with the associated limits on working flow and penstock 

length resulted in a total hydropower potential of 30,000 MWa. This amount of 

potential power is on the order of the total annual average power of the entire 

existing U.S. hydroelectric plant population. The approximately 5,400 sites that 

could potentially be developed as small hydro plants have a total hydropower 

potential of a little over 18,000 MWa. If developed, these projects would result in 

a greater than 50% increase in hydroelectric generation. 

The regional results were parsed into results for the individual 50 states 

using GIS tools. Gross power potentials and hydropower potentials for feasible 

v 
potential projects are presented for each state. Six western states, Alaska, 

Washington, California, Idaho, Oregon, and Montana, have the highest power 

potentials. From the perspective of the density of hydropower potential 

(kWa/sq mi) that could feasibly be developed, Hawaii and Washington have the 

highest densities of feasibly developable resources. By comparing hydropower 

potential associated with feasible projects to the total annual average power of 

the existing hydroelectric plants in the state, it was found that 33 states could 

increase their hydropower generation by 100% or more and 41 states could 

realize increases of more than 50%. A map showing the locations of the feasible 

potential project sites indicates that with the exceptions of part or most of eight 

states, potential projects are abundant throughout the country. Summaries of the 

gross and feasible potential in each state are provided in Appendix B. 

It is concluded from the study results that there are a large number of 

opportunities for increasing U.S. hydroelectric generation throughout the country 

that are feasible based on an elementary set of feasibility criteria. These 

opportunities collectively represent a potential for approximately doubling U.S. 

hydroelectric generation (not including pumped storage), but more realistically 

offer the means to at least increase hydroelectric generation by more than 50%. 

Compared to current in-state hydroelectric generation, nearly all of the states are 

underutilizing their natural stream water energy resources and could realize 

significant gains in generation from new hydroelectric plant development. 

Western states, including Alaska and Hawaii, have particularly large feasible 

hydropower potentials or densities of feasible hydropower potential. The 

majority of the identified feasible hydropower potential could be harnessed 

without constructing new dams, using existing techniques and technologies 

developed over the long and extensive history of installing small hydroelectric 

plants in the U.S. 

The results of the prior assessment of water energy resources and this 

feasibility study have been incorporated into a GIS application accessible on the 

Internet at: http://hydropower.inl.gov/prospector. The application named the 

Virtual Hydropower Prospector (VHP) displays sites on hydrologic region maps. 

In addition to the sites, the user can select what context features are displayed, 

including hydrography, the power system, transportation, areas and places, and 

land use. Tools to select features and display their attributes are provided along 

with standard map navigation tools. The application has a print capability so that 

any map the user creates can be printed or incorporated into a document or slide 

show. VHP extends and enhances this report by providing detailed information 

about water energy resource sites and feasible potential projects and providing 

sufficient information for users to conduct specialized, preliminary feasibility 

assessments. 

The last section in the report provides recommendations for additional 

studies. These include: refining the feasibility assessment by considering 

additional factors affecting feasibility and true hydropower potential; upgrading 

VHP by displaying high resolution topography and additional context feature 

sets; using the data produced in the prior and present study to produce 

customized reports of resources on military bases and tribal lands; performing 

natural stream resource and feasibility studies for other countries; performing 

similar assessments for other water energy resources such as ocean, tidal, and 

vi 
constructed waterways; and producing a catalog of technologies and cost 

estimating tools for small hydroelectric plants. These studies have the common 

objective of facilitating the planning and development of small hydroelectric 

plants with their attendant benefits using diverse technologies at locations around 

the globe. 

For further information or comments, please contact: 

Douglas G. Hall, Project Manager 

Small Hydropower Resource Assessment and Technology Development Project 

Idaho National Laboratory 

P.O. Box 1625, MS 3830 

Idaho Falls, ID 83415-3830 

Phone: (208) 526-9525 

E-mail: douglas.hall@inl.gov
 

vii 
viii 
ACKNOWLEDGMENTS 

The authors acknowledge and express their appreciation for the 

contributions to this study made by the U.S. Geological Survey: Earth Resources 

Observation Systems Data Center for producing the Elevation Derivatives for 

National Applications (EDNA) datasets for the 20 hydrologic regions of the 

United States, including high resolution synthetic hydrography, and 

programming and data processing, using the EDNA data in conjunction with 

climatic data to produce the basic power potential datasets and elevation 

annotated synthetic hydrography with particular recognition of the contributions 

of Ms. K. L. Verdin and Mr. M. Cast. The authors acknowledge and express their 

appreciation of project team member Ms. S. E. White, who produced the Virtual 

Hydropower Prospector GIS application that extends access to and the utility of 

the study results presented in this report. The authors acknowledge and express 

their appreciation for the technical editing and word processing of this document 

by Ms. J. K. Wright and Ms. D. R. Southwick, respectively. The authors 

acknowledge and express their appreciation for the technical guidance provided 

by members of the project technical advisory committee who are too numerous to 

mention by name. Particular acknowledgment and appreciation of 

Ms. P. A. Brookshier of the U.S. Department of Energy Idaho Operations Office 

is expressed for requesting the resource assessment research culminating in this 

report. 

ix 
x 
CONTENTS 

ABSTRACT.................................................................................................................................................iii
 

SUMMARY.................................................................................................................................................. v
 

ACKNOWLEDGMENTS ........................................................................................................................... ix
 

ACRONYMS.............................................................................................................................................. xv
 

NOMENCLATURE .................................................................................................................................xvii
 

1. INTRODUCTION.............................................................................................................................. 1
 

2. STUDY AREA⎯TWENTY HYDROLOGIC REGIONS OF THE UNITED STATES .................. 4
 

2.1 Geographic Description......................................................................................................... 4
 

2.2 Existing Hydroelectric Plants................................................................................................ 7
 

3. TECHNICAL APPROACH ............................................................................................................... 8
 

3.1 Water Energy Resource Site Population ............................................................................... 8
 

3.2 Site Hydropower Potential .................................................................................................... 9
 

3.2.1	 Project Penstock Length.................................................................................... 10
 

3.2.2	 Project Working Flow Rate............................................................................... 13
 

3.2.3	 Logic for Selecting Site Development Parameters............................................ 13
 

3.2.4	 Summary of Site Development Criteria for Estimating Project Hydropower 

Potential............................................................................................................. 14
 

3.3 Project Feasibility Criteria................................................................................................... 14
 

3.4 Identification of Feasible Potential Projects........................................................................ 17
 

4. RESULTS......................................................................................................................................... 19
 

4.1	 Power Category Distribution of Assessed Water Energy Resource Site Population .......... 19
 

4.2	 Power and Technologies Class Distribution of Feasible Potential Projects ........................ 21
 

4.3	 Spatial Distribution of Water Energy Resources and Potential Projects............................. 24
 

4.4	 Potential Project Location and Attributes Provided by the Virtual Hydropower 

Prospector............................................................................................................................ 33
 

5. CONCLUSIONS .............................................................................................................................. 35
 

6. RECOMMENDATIONS ................................................................................................................. 37 
 

7. REFERENCES................................................................................................................................. 39
 

xi 
Appendix A—Description of Exclusion Zones........................................................................................A-1
 

Appendix B—Assessment Results by State ................................................................................B-1 

FIGURES 

1.	 The 20 hydrologic regions (units) of the United States...................................................................... 5
 

2.	 Power class distribution of U.S. hydroelectric plants and their total average power. ........................ 7
 

3. Power class distributions of U.S. water energy resource sites by number and gross power 

potential. ............................................................................................................................................. 9
 

4.	 Penstock lengths of low power hydroelectric plants in the Pacific Northwest Region. ................... 10
 

5.	 Number of low power hydroelectric plants in the Pacific Northwest Region by penstock 

length interval and cumulative percentage of plants having penstocks of a given length or 

shorter............................................................................................................................................... 11
 

6.	 Penstock lengths of small hydroelectric plants in the Pacific Northwest Region. ........................... 11
 

7.	 Number of small hydroelectric plants in the Pacific Northwest Region by penstock length 

interval and cumulative percentage of plants having penstocks of a given length or shorter. ......... 11
 

8. Penstock length upper limits for low power and small hydro plants in 20 U.S. hydrologic 

regions. ............................................................................................................................................. 12
 

9.	 Logic for determining whether a water energy resource site should be developed as a low 

power or small hydro project using development criteria thereby establishing working flow 

rate, penstock length, working hydraulic head, and hydropower potential. ..................................... 15
 

10.	 a) Distribution of the distance of low power and small hydroelectric plants to a city or 

population center boundary. b) Cumulative distribution of the distance of low power and 

small hydroelectric plants to a city or population center boundary.................................................. 17
 

11.	 Power category distribution of water energy resource sites having gross power potentials 

greater than or equal to 10 kWa and their associated total gross power potential............................ 19
 

12.	 Operating envelopes of three classes of low power technologies. ................................................... 21
 

13. Power category distribution of feasible potential projects and their associated total 

hydropower potential with low power projects further divided by low power technology 

classes............................................................................................................................................... 22
 

14.	 Distribution of (a) number and (b) group hydropower potential of U.S. low power potential 

projects. ............................................................................................................................................ 23
 

15.	 Distribution of (a) number and (b) group hydropower potential of U.S. small hydro 

potential projects. ............................................................................................................................. 24
 

xii 
16. Total gross power potential of water energy resources in the 50 states of the United States 

divided into feasible, other available, excluded, and developed power categories. ......................... 25
 

17. Total gross power potential density of water energy resources in the 50 states of the United 

States divided into feasible, other available, excluded, and developed power categories................ 27
 

18. Total hydropower potential of feasible low power and small hydro projects in the 50 states 

of the United States. ......................................................................................................................... 28
 

19.	 Total hydropower potential density of feasible low power and small hydro projects in the 

50 states of the United States............................................................................................................ 29
 

20. Existing hydroelectric plants and feasible potential hydropower projects in the United 

States. ............................................................................................................................................... 31
 

21. Desktop of the Virtual Hydropower Prospect GIS application showing its areas for display
 

and control........................................................................................................................................ 34
 

TABLES 

1.	 Hydrologic regions of the United States............................................................................................. 4
 

2.	 Penstock upper limits for low power and small hydro plants by hydrologic region. ....................... 13
 

3.	 Distances of 90% of low power and small hydro plants from cities and populated area 

boundaries in 20 hydrologic regions. ............................................................................................... 17
 

4. GIS data layers used for proximity analyses. ................................................................................... 18
 

5. Water energy resource site attributes used in development feasibility assessment.......................... 18
 

6.	 Power potential of U.S. water energy resource sites in power categories divided into power 

classes and low power technology classes. ...................................................................................... 22
 

7. Comparison of hydropower potential of feasible potential projects with total annual 

average power of hydroelectric plants in each of the 50 states of the United States........................ 26
 

xiii 
xiv 
ACRONYMS 

BNI	 Bechtel National, Incorporated 

DEM digital elevation model 

DOE	 U.S. Department of Energy 

EDNA Elevation Derivatives for National Applications 

An analytically derived, three-dimensional dataset in which hydrologic features have 

been determined based on elevation data from the National Elevation Dataset, resulting in 

three-dimensional representations of “synthetic streams” (stream path coordinates plus 

corresponding elevations) and an associated catchment boundary for each synthetic reach 

(based on 1:24K-scale data for the conterminous United States and 1:63,360-scale data 

for Alaska) (Note: EDNA synthetic stream reaches do not uniformly coincide with NHD 

reaches. Conflation of EDNA and NHD features to improve the quality of both datasets is 

a later phase EDNA development.) (http://edna.usgs.gov) 

EROS	 Earth Resources Observation Systems 

FERC Federal Energy Regulatory Commission 

GIS geographic information system 

A set of digital geographic information, such as map layers and elevation data layers, 

which can be analyzed using both standardized data queries as well as spatial query 

techniques. 

HPRA	 Hydroelectric Power Resources Assessment 

HUC hydrologic unit code 

INL Idaho National Laboratory 

NHD	 National Hydrography Dataset 

A comprehensive set of digital spatial data that contains information about surface water 

features such as lakes, ponds, streams, rivers, springs, and wells. (http://nhd.usgs.gov) 

NPS Nuclear Placement Services 

USGS	 U.S. Geological Survey 

VHP Virtual Hydropower Prospector 

xv 
xvi 
NOMENCLATURE 

Annual mean flow rate The statistical mean of the flow rates occurring at a particular location during 

the course of 1 year. The annual mean flow rates were estimated using regional 

flow regression equations based on gauged stream flow rates that occurred over 

a period of many years. The annual mean flow rate in any given year will 

usually differ from the value predicted by the equations. 

Annual mean power The statistical mean of the rate at which energy is produced over the course of 

1 year. When based on the predicted annual mean flow rate and associated 

hydraulic head at a water energy resource site or based on working fractions of 

these quantities associated with a feasible potential project, the predicted 

annual mean power is the mean of the annual mean powers occurring over a 

period of many years. Such power values are denoted by units of “kWa” or 

“MWa”. The actual annual mean power in a specific year will usually differ 

from the predicted value. 

A power rating of a hydroelectric plant based on electricity generation at this 

rate throughout the course of a year would produce the average annual 

electricity generation of the plant; sometimes referred to as average megawatt 

power rating denoted in some usages by “MWa.” 

Attribute Characteristic information about a feature such as name or owner, or data 

describing it such as length or voltage. 

Capacity Typically refers to the design power rating of a hydroelectric plant and are 

denoted by units of “MW. Considering all U.S. hydroelectric plants, the 

average ratio of capacity to annual mean power is a factor of two. 

Catchment The local drainage area surrounding a stream reach that provides runoff to the 

reach as opposed to flow entering the reach at its upstream end resulting from 

runoff from upstream catchments. 

Drainage area The total surface area of the topography of a drainage basin. 

Drainage basin The geographic area supplying runoff to a particular point on a stream equal to 

the area of all the catchments associated with upstream stream reaches 

supplying flow to the point. 

EDNA stream node Starting point of an EDNA synthetic stream, a confluence on it or point of 

reference, or its terminus where it enters a saltwater body or a sink. 

EDNA stream reach That portion of an EDNA synthetic stream between two EDNA stream nodes. 

(Note: Each stream reach has an associated local catchment and an associated 

drainage basin.) 

Exclusion zone An area in which hydroelectric plant development is highly unlikely due to 

federal land use statutes or policies or environmental sensitivities. 

Feasible potential 

project 

A water energy resource site that has met a set of feasibility criteria, 

thus identifying it as feasible for development 

Gross hydraulic head The hydraulic head corresponding to the difference in the elevations at the 

upstream and downstream ends of a stream reach comprising a water energy 

resource site. 

xvii 
Gross power potential Ideal hydroelectric power based on an annual mean flow rate and an associated 

gross hydraulic head having units of MWa (average megawatts) in this report. 

The actual value in any given year will usually differ from the predicted value 

because of annual variations in annual mean flow rate. (Note: In the case of the 

developed power potential of an actual hydroelectric plant, annual mean power 

[average power] of the plant is used as the developed power potential.) 

Hydraulic head The elevation difference between the upstream and downstream ends of a 

column of water (such as in a penstock). 

Hydropower potential The power potential of a feasible potential project based on its working flow 

rate and working hydraulic head having units of MWa (average megawatts) in 

this report. 

Map server An internet-based application that displays geographic information on a map. 

Penstock A pipe conducting water from the point of takeoff on a stream to a turbine. 

Power category The power category names used in this report to differentiate between 

categories of power potential are: “total,” “developed,” “excluded,” “available” 

and “feasible.” Total refers to all the power potential in a study area. 

Developed refers to the power potential corresponding to the sum of the annual 

mean power of all the existing hydroelectric plants in a study area. Excluded 

refers to the power potential existing within zones in a study area where 

hydropower development is highly unlikely based on federal law or policy or 

known environmental sensitivities. Available refers to power potential 

corresponding to water energy resource sites that are not located in zones 

where hydropower development is unlikely and are not collocated with an 

existing hydroelectric plant. (Note: Available does not denote availability 

based on ownership or control.) Feasible refers to power potential 

corresponding to water energy resource sites that have met the limited set of 

feasibility criteria used in this study. (Note: The actual feasibility of a specific 

site must be determined by a comprehensive evaluation performed by a 

perspective developer.) 

Power class 

(water energy 

resource sites) 

The power and technology classes into which water energy resource sites have 

been divided based on their power potential and gross hydraulic head: 

• High Head/High Power 

• Low Head/High Power 

• High Head/Low Power 

• Convention Turbine 

• Unconventional Systems 

• Microhydro 

where high power refers to ≥1 MWA, low power refers to <1 MWA, high head 

refers to ≥30 ft, and low head refers to <30 ft. The conventional turbines, 

unconventional systems, and microhydro power technology classes are 

subclasses of the low power class defined by their operating envelopes as 

shown in the figure below. 

xviii 
Power class The power and technology classes into which feasible potential projects have 

(feasible potential been divided based on their hydropower potential and working hydraulic head: 

projects) 

• Small Hydro 

• Low Head-Convention Turbines 

• Low Head-Unconventional Systems 

• Microhydro 

where small hydro refers to hydropower potential ≥1 MWA and ≤ 30 MWA, 

and low power refers to hydropower potential <1 MWA. The conventional 

turbines, unconventional systems, and microhydro power technology classes 

are subclasses of the low power class defined by their operating envelopes as 

shown in the figure above except with no upper limit on hydraulic head for 

conventional turbines. When referring to the above figure for feasible potential 

projects, power (“1 Megawatt” or “100 kW”) is hydropower potential, “Flow 

Rate” is working flow rate, and “Hydraulic Head” is working hydraulic head. 

Reach	 A stream segment often delineated by two successive confluences. 

Region One of the 20 hydrologic regions into which the United States is divided, each 

composed of a set of drainage basins; in general, all flowing to the same stream 

or streams through which water flows out of the region. Regions are designated 

by hydrologic unit codes (HUC) from 1 through 20. 

VHP desktop The Virtual Hydropower Prospector (VHP) GIS application desktop displayed 

in a single window and composed of the map view and controls for selecting 

the graphical and numerical information displayed by the application. (Note: 

Multiple windows each containing a complete VHP desktop devoted to a 

different hydrologic region may be open at the same time.) 

Water energy A stream reach for which the values of hydraulic head, annual mean flow rate, 

resource site and power potential have been estimated. The site location is taken as the 

longitudinal midpoint of the reach. 

Working flow rate The rate of flow of water through a turbine. 

Working head The hydraulic head equal to the difference in the elevations of the entrance and 

exit of a penstock. 

xix 
xx 
 

 

Feasibility Assessment of the Water Energy 

Resources of the United States for 

New Low Power and Small Hydro Classes of 

Hydroelectric Plants
 

1. INTRODUCTION 

In June 1989, the U.S. Department of Energy 

(DOE) initiated the development of a National 

Energy Strategy to identify the energy resources 

available to support the expanding demand for 

energy in the United States. Past efforts to identify 

and measure the undeveloped hydropower 

capacity in the United States have resulted in 

estimates ranging from about 70,000 MW to 

almost 600,000 MW. The Federal Energy 

Regulatory Commission’s (FERC’s) capacity 

estimate was about 70,000 MW, and the U.S. 

Army Corps of Engineers’ theoretical estimate 

was 580,000 MW. Public hearings conducted as 

part of the strategy development process indicated 

that the undeveloped hydropower resources were 

not well defined. One of the reasons was that no 

agency had previously estimated the undeveloped 

hydropower capacity based on site characteristics, 

stream flow data, and available hydraulic heads. 

As a result, DOE established an interagency 

Hydropower Resources Assessment Team to 

ascertain the country’s undeveloped hydropower 

potential. The team consisted of representatives 

from each power marketing administration 

(Alaska Power Administration, Bonneville Power 

Administration, Western Area Power 

Administration, Southwestern Power 

Administration, and Southeastern Power 

Administration), the Bureau of Reclamation, the 

Army Corps of Engineers, the FERC, the Idaho 

National Laboratory (INL), and the Oak Ridge 

National Laboratory. The interagency team drafted 

a preliminary assessment of potential hydropower 

resources in February 1990. This assessment 

estimated that 52,900 MW of undeveloped 

hydropower capacity existed in the United States. 

Partial analysis of the hydropower resource 

database by groups in the hydropower industry 

indicated that the hydropower data included 

redundancies and errors that reduced confidence in 

the published estimates of developable 

hydropower capacity. DOE has continued 

assessing hydropower resources to correct these 

deficiencies, improve estimates of developable 

hydropower, and determine future policy. An 

assessment of the opportunities for increased 

hydropower capacity in the United States 

identified 5,677 sites having a total capacity 

increase potential of about 70,000 MW (Connor 

et al. 1998). Consideration of environmental, legal, 

and institutional constraints resulted in an estimate 

of about 30,000 MW of viable opportunities to 

increase the United States hydropower capacity. 

The previous resource assessment 

(Connor et al. 1998) was a site-based assessment, 

which evaluated the potential for obtaining 

increased hydropower capacity at previously 

identified sites. During the 2002 to 2004 

timeframe, INL conducted regional assessments 

and then a national assessment of the power 

potential of all streams in the study area 

culminating in a report documenting the power 

potential of all United States natural streams 

(Hall et al. 2004). This comprehensive assessment 

conducted in conjunction with the U.S. Geological 

Survey (USGS) used state-of-the-art digital 

elevation models and geographic information 

system (GIS) tools to estimate the power potential 

of a mathematical analog of every stream segment 

in the country. Summing the estimated power 

potential of all stream segments provided an 

estimate of the total power potential of U.S. natural 

streams. The study only assessed water energy 

resources associated with natural water courses 

(constructed waterways, tides, waves, and ocean 

currents were not included). 

While the gross power potential estimates in 

the 2004 report are useful, the greatest insight 

gained from the reported results is the relative 

magnitudes when power potentials are compared. 

1 
 

 

Comparison of the magnitudes of state and 

regional power potentials and potential power 

densities shows those areas of the country having 

the most abundant and concentrated water energy 

resources. The spatial distribution maps included 

in the report also provide a visual measure of the 

relative concentration of water energy resources in 

the country. Comparison of developed, excluded, 

and available power potentials to the total power 

potential provides relative measures of these 

quantities that can be compared between areas to 

see the trends of past policy and development 

decisions and opportunities for future 

development. Comparison of power potential in 

the various power classes shows the relative 

abundance of water energy resources having 

certain hydraulic head and power characteristics, 

which can be used to guide future technology 

development. 

Having completed the comprehensive 

assessment of the United States natural stream 

resources, the project addressed the ultimate 

resource questions: 

•	 Which of the identified water energy resource 

sites can feasibly be developed? 

•	 How much power can realistically be 

generated at the sites that are feasible? 

•	 Where are the feasible potential project sites 

located? 

The study reported in this document generated 

information that answers these questions. 

Feasibility criteria including exclusion of 

development, site accessibility, and transmission 

and load proximity were used to identify which 

water energy resource sites are locations for 

feasible potential projects. Development criteria 

regarding working flow rate and realistic penstock 

lengths were used to determine estimates of the 

realistic power potential of the feasible potential 

projects. The low power or small hydro project 

model that was used assumed power production 

without total stream impoundment or the creation 

of a reservoir.a

 Since the project worked with georeferenced data from inception, the location of 

feasible potential projects was known once they 

were identified. While the report contains a 

distribution map showing the locations of feasible 

projects, this map is most valuable for detecting 

gross concentrations of projects. A companion 

GIS application called the Virtual Hydropower 

Prospector (VHP), which is available on the 

Internet (http://hydropower.inl.gov/prospector), 

was produced as a tool for locating water energy 

resource sites and feasible potential projects and 

performing customized, preliminary feasibility 

assessments. 

As with the results in the predecessor report, 

the reader is cautioned about an important 

distinction that is made in the presentation of 

power results in this report. The assessment 

method that was used produced estimates of power 

potential as annual mean power. This parameter is 

not the same as hydropower capacity, which has 

been assessed in other assessment efforts. The 

difference lies in potential being based on 

estimates of annual mean flow rate or a working 

fraction thereof combined with gross or working 

hydraulic head to produce an estimate of annual 

mean power potential. In contrast, hydropower 

capacity is the design power capacity of a real or 

hypothetical hydroelectric plant. Plant design 

capacity is derived based on anticipated flow rates, 

which may not be natural stream flows, and may 

be determined by economic considerations, and 

other factors. Because the assessment results are 

power potential values rather than plant capacity 

values, total power potential values listed in this 

report will appear low when compared with the 

results of prior assessments, which are based on 

owners’ selections of design capacity or an 

economic model that selects a design capacity. 

The values listed in this report are directly 

convertible to generation by multiplying them by 

the number of hours in a year without the need to 

apply a capacity factor. 

a. The development plant model included entry of part of the 

stream flow into a penstock running parallel to the stream 

channel leading to a powerhouse downstream of which the 

water was returned to the stream. Entry to the penstock could 

be accomplished by water takeoff at a bend, obstructing a 

secondary channel to create a power channel, or the use of a 

submerged weir. 

2 
This report is organized by presenting a 

description of the study area, details of the 

methods that were employed to perform the 

assessment, results of the assessments considering 

the study area at large, general conclusions based 

on the study results, and recommendations for 

additional related research. Appendix A describes 

the exclusion zones used in the study. Appendix B, 

which is a major fraction of the volume, contains 

summaries of the study results for each of the 

50 states. 

3 
 

 

2. STUDY AREA⎯TWENTY HYDROLOGIC REGIONS 

OF THE UNITED STATES 

The United States is divided into 20 hydrologic 

regions designated by the USGS that are shown in 

Figure 1. The hydrologic regions have been 

numbered using a hydrologic unit code (HUC) of 

1 through 20. For example, the North Atlantic 

Hydrologic Region has been assigned a hydrologic 

unit code of 1 and is sometimes referred to as 

“HUC 1.” Eighteen hydrologic regions, HUC 1 

through HUC 18, have been assigned to the 

conterminous United States. The remaining two 

hydrologic regions, HUC 19 and HUC 20, are 

assigned to Alaska and Hawaii, respectively. An 

additional region assigned to Puerto Rico, HUC 21, 

was not evaluated during this study. The hydrologic 

regions are listed by region or HUC number in 

Table 1. 

Table 1. Hydrologic regions of the United States. 

Region 

(HUC) 

No. Name 

1 North Atlantic 

2 Mid-Atlantic 

3 South Atlantic-Gulf 

4 Great Lakes 

5 Ohio 

6 Tennessee 

7 Upper Mississippi 

8 Lower Mississippi 

9 Souris Red-Rainy 

10 Missouri 

11 Arkansas-White-Red 

12 Texas Gulf 

13 Rio Grande 

14 Upper Colorado 

15 Lower Colorado 

16 Great Basin 

17 Pacific Northwest 

18 California 

19 Alaska 

20 Hawaii 

2.1 Geographic Description 

The conterminous United States from east to 

west consists of a coastal plain along the Atlantic, 

the Appalachian Mountains, a vast interior 

lowland, and the western Cordillera, which is a 

wide system of mountains and valleys extending 

to the Pacific Ocean. The Atlantic Coastal plain is 

narrow in the mid-Atlantic states, but gradually 

widens toward the south to form a broad coastal 

plain in the Carolinas and Georgia. Estuaries and 

bays form deep indentations in the coastal plain, 

especially Delaware Bay and Chesapeake Bay in 

Delaware, Maryland, and Virginia. Inland from 

the coastal plain, the Piedmont forms a gentle 

rolling upland that borders the eastern slope of the 

Appalachians. The Appalachian Mountains form a 

long southwest-northeast trending chain of 

mountains that extend from northern Alabama to 

New England. From New York southward, the 

Appalachians are composed of a long series of 

alternating ridges and valleys, created by folding 

and erosion of ancient rock layers. The mountains 

continue into New England, but the ridge and 

valley pattern is absent. Breaks in mountain 

ridges, known as “water gaps,” allow several 

major rivers to cross part or all of this mountain 

chain, for example, the Connecticut River in New 

England, the Hudson River in New York, the 

Delaware River in Pennsylvania, the Susquehanna 

River in New York, Pennsylvania, and Maryland, 

and the Potomac River in Virginia, West Virginia, 

and Maryland. 

West of the Appalachians lies a vast interior 

lowland that covers nearly half of the 

conterminous United States. It includes the 

drainage of the Mississippi River and its two 

major tributaries, the Ohio and Missouri rivers. 

The Mississippi River is the principal feature of 

this lowland, forming a major north-south 

waterway into the heartland of the United States. 

The lowland includes a wide coastal plain 

bordering the Gulf of Mexico, with rolling hills, 

river valleys, and extensive prairies lying north of 

the coastal plain. Dense deciduous woodlands 

4 
M b • 2Q I 

.... "" "" ;m Elev ation Key (feet) 

- • I 

7,400 14 ,500 M les 

ffi '00 "" 

13,EOJ 

Figure 1. The 20 hydrologic regions (units) of the United States. 

5 
originally covered the eastern portion of the 

lowland, transitioning to pine forests in the south. 

Further west, the woodland gives way to prairie, a 

vast grassland mostly devoid of trees. Much of the 

woodland and prairie has been converted to 

agricultural use. The climate ranges from warm in 

the south to cold in the north, with precipitation 

decreasing toward the west. 

A complex series of high mountain ranges, 

valleys, canyons, and plateaus create a spectacular 

landscape in the western United States. The Great 

Plains, which form the western portion of the 

interior lowlands, gradually rise thousands of feet 

in elevation to meet the abrupt eastern front of the 

Rocky Mountains. The Rocky Mountains are a 

chain of high mountain ranges extending from 

Mexico through the western United States into 

Canada. The crest of the Rocky Mountains forms 

the continental divide. Streams east of the 

continental divide flow to the Atlantic Ocean, the 

Gulf of Mexico, and the Hudson Bay. Most 

streams west of the continental divide flow to the 

Pacific Ocean or to the Gulf of California. 

However, streams in many areas west of the 

continental divide discharge into saline lakes or 

mud flats. These streams remain within the Great 

Basin, a series of semi-arid to arid mountains, 

valleys, and plains with no outlet to the sea. More 

high mountains are found in the West Coast states: 

the Cascades in Washington and Oregon and the 

Sierra Nevada in California. An additional set of 

mountain ranges, known as the Coast Ranges, 

borders the Pacific coastline of these three states. 

The landscape varies greatly in the West. 

Cool, damp rainforests cover the slopes of the 

Coast Ranges in the Pacific Northwest. The 

Cascades and the Sierra Nevada have extensive 

coniferous forests due to abundant Pacific 

moisture. However, these ranges create a rain 

shadow that forms dry steppes and deserts 

immediately to their east. The two major rivers of 

the West, the Columbia River and the Colorado 

River, have been extensively developed for 

hydropower. The Grand Coulee Dam in 

Washington and the Hoover Dam on the 

Nevada-Arizona border are the best known of the 

West’s hydropower mega-projects. Interior valleys 

have fertile soils suitable for farming, including 

the Great Central Valley of California, the 

Willamette Valley of Oregon, and the Snake River 

Plain in Idaho. In many places, irrigation water 

from mountains or rivers is imported to water 

crops in arid areas. Water is also imported for 

hundreds of miles to supply the domestic needs of 

major coastal cities in California. 

Alaska, the largest, northernmost, and least 

densely populated state, extends from temperate 

rainforests on the southeastern panhandle, to arctic 

tundra on the arid North Slope. High coastal and 

near-coastal mountain ranges receive abundant 

Pacific moisture as snow and ice to create the 

largest glaciated area outside of Antarctica and 

Greenland. Further inland, the Alaska Range 

reaches elevations exceeding 20,000 feet on 

Mt. McKinley, the highest point in North America. 

Approximately one-third of the state lies north of 

the Arctic Circle. 

A large interior lowland, extending across the 

central portion of the state, is drained primarily by 

the Yukon River and its tributaries. Rivers and 

streams in this area are typically braided and are 

subject to intense season flooding due to rapid 

melting of snow and ice during the spring/summer 

thaw. The east-west trending Brooks Range lies 

north of this lowland. North of the Arctic Circle, 

the North Slope, a flat, arid plain slopes northward 

from the Brooks Range to the Arctic Ocean. 

Permafrost and tundra dominate the North Slope, 

home to the Arctic National Wildlife Refuge, as 

well as some of the United States’ most productive 

oil fields. 

Hawaii, a chain of eight volcanic islands, lies 

near the center of the Pacific Ocean, 

approximately 2,200 miles from the U.S. 

mainland. The island chain was formed by motion 

of the Pacific Plate over a stationary volcanic hot 

spot that extrudes molten rock to create a series of 

volcanic islands. The islands nearest to the hot 

spot, Hawaii and Maui, have active volcanoes and 

are the largest islands in the chain. Islands further 

from the hot spot no longer contain active 

volcanoes and are generally smaller due to 

subsidence and erosion. Islands with northern and 

eastern exposures to the Pacific receive abundant 

moisture up to several hundred inches per year. 

The opposite southern and western slopes lie in a 

rain shadow, where arid conditions predominate. 

6 
Some of the smaller islands are relatively dry 

because they lie entirely within the rain shadow of 

larger islands. 

The Hawaiian Islands lack the large 

watersheds found on the U.S. mainland. Instead, 

streams on the islands generally run outward in a 

radial pattern from volcanic summits and 

mountain ridges toward the sea. The largest 

streams with the highest flow levels are found on 

the wetter northern and eastern slopes of the major 

islands. 

2.2 Existing Hydroelectric 

Plants 

The Hydroelectric Power Resources 

Assessment (HPRA) Database (FERC 1998) lists 

2,378 hydroelectric plants in the United States (not 

including pumped storage plants). The distribution 

of these plants by power class is shown in 

Figure 2. The power classes are defined on the 

basis of annual average power [Pa = Annual 

Generation/Annual Hours (8,760 hr)] rather than 

by design capacity. They include: 

• Low power: Pa < 1 MWa 

• Small hydro: 1 MWa ≤ Pa ≤ 30 MWa 

• Large hydro: Pa > 30 MWa. 

The plant population produces energy at a 

total annual average rate of 35,432 MWa based on 

the average annual generation data in the HPRA 

Database. The 192 large hydro plants, which are 

only 8% of the plant population, produce 80% of 

the annual average power. On the other hand, 

2,184 low power and small hydro plants constitute 

92% of the plant population and produces the 

remaining 20% of the annual average power. 

Clearly, the public perception of hydroelectric 

plants is based on a small percentage of the plant 

population almost certainly without recognition 

that the vast majority of hydroelectric plants are 

small or very small plants. 

Figure 2. Power class distribution of U.S. hydroelectric plants and their total average power. 

7 
3. TECHNICAL APPROACH 

Water energy resource sites in each of 

20 hydrologic regions identified in the assessment 

of U.S. water energy resources (Hall et al. 2004) 

were assessed with regard to the feasibility of their 

development and the power potential of feasible 

sites considering development constraints. The 

feasibility assessment thus had two components: 

•	 Selection of sites based on project feasibility 

criteria 

•	 Estimation of power potential using realistic 

development criteria. 

The technical approach as originally 

envisioned was first to identify sites that could 

feasibly be developed and then estimate the power 

potential of these sites using a development model 

with associated, realistic development constraints. 

During the evolution of the technical approach, it 

was determined that it would be necessary to first 

estimate the realistic power potential of all the 

sites and then determine the feasibility of their 

development. This approach was required because 

the assessment methodology that was finally 

employed required knowing the ultimate power 

class (low power or small hydro) of a potential 

project based on realistic development criteria as a 

prerequisite for applying one of the 

load/transmission proximity feasibility criteria. 

The detailed description of the technical 

approach addresses: 

•	 The population of U.S. water energy resource 

sites that were assessed 

•	 Estimation of the power potential of these sites 

based on a development model with associated 

development constraints 

•	 Identification of feasible potential projects 

based on a set of feasibility criteria. 

Some of the feasibility and development criteria 

were selected based on engineering judgment. The 

rationale for each of these selections is provided in 

the discussion. Others were derived from 

characteristics of the existing hydroelectric plant 

population in each region. 

The feasibility assessment was performed on a 

region by region basis. The results for the 

20 hydrologic regions were combined to obtain 

nationwide results. Results for each of the 

50 states were obtained by intersecting regional 

data with state boundaries. This was possible 

because of the water energy resource site data 

produced in the prior resource assessment and 

further attributed in the present study was 

georeferenced. 

3.1 Water Energy Resource Site 

Population 

The water energy resource sites that were 

assessed for development feasibility corresponded 

to all the validated stream reaches in the country 

having a gross power potential greater than 

10 kWa. Validated stream reaches were segments 

of synthetic streams having an associated 

catchment area that contained a part of a stream in 

the National Hydrography Dataset (NHD). The 

validated reaches averaged 2 miles in length. The 

longitudinal midpoint of the reach was used as the 

geographic location of the water energy resource 

site. 

The site population on which the feasibility 

assessment was performed numbered 

approximately 500,000 sites having gross power 

potentials greater than 10 kWa. The total number 

of sites countrywide was over one million. The 

distribution of water energy resource sites by the 

number of sites in each of three power classes (see 

Subsection 2.2 for power class definitions) and the 

corresponding, total, gross power potential of the 

sites is shown in Figure 3. 

The site population assessed represented a total 

gross power potential of nearly 300,000 MWa. 

Figure 3 shows that over 99% of the feasibility 

assessed, water energy resource site population are 

low power and small hydro sites corresponding to 

74% of the total gross power potential. There are a 

relatively small number of large hydro sites (874) 

that correspond to the remaining 26% of the total 

gross power potential if found to be feasible. The 

large hydro sites could be developed as low power 

or small hydro plants through partial use of the 

resource. 

8 
Large Hydro

874,

0.2%

Small Hydro

43,533

9%

Low Power 

455,750

91%

Low Power

 60,243

20%

Large Hydro

 77,187

 26% Small Hydro

160,006

54%

Large Hydro Small Hydro 874, 43,533 0.2% 9% 

Large Hydro

 77,187

 26% Small Hydro 

160,006 

54% 

Low Power 

455,750 Low Power

91% 60,243 

500,157 sites 

20% 

Total Gross Power Potential 

297,436 MWa 

Figure 3. Power class distributions of U.S. water energy resource sites by number and gross power 

potential. 

3.2 Site Hydropower Potential 

The gross power potential of each water 

energy resource site was defined by the annual 

mean flow rate of the associated reach and gross 

hydraulic head equal to the elevation difference 

between the upstream and downstream ends of the 

reach. Use of the entire reach flow and 

installations of penstocks of 10,000 ft long on 

average, which was the average reach length, are 

not realistic for most low power and small hydro 

plants. It was, therefore, necessary to define a 

basic model for site development incorporating 

limitations on both the usable flow and the 

penstock length to estimate the true hydropower 

potential of the site. 

The basic development model assumed was a 

hydroelectric plant producing power at an annual 

average rate of 30 MWa or less. The plant 

configuration did not include a dam obstructing 

the main stream channel and did not include water 

impoundment in its operation. The most simplistic 

version of the working model includes a water 

takeoff point on the stream bank at which water 

enters a penstock running parallel to the stream 

channel terminating at a powerhouse containing a 

single turbine-generator set. Downstream of the 

powerhouse, the water is returned to the stream 

channel. Induction of the water into the penstock 

may be by means of the takeoff point being at a 

natural bend in the stream channel or use of a 

submerged diversion structure. It is also possible 

that a secondary branch of the stream is obstructed 

to produce a power channel from which water 

enters the penstock. Depending on the path of the 

stream channel, it is also possible that the penstock 

could run transverse to the stream channel 

terminating at a powerhouse located at a lower 

elevation beside the stream. However, this 

configuration was not considered in the feasibility 

assessments. 

The realistic power potential of each water 

energy resource site was estimated by assigning 

limitations on working flow rate and penstock 

length within the context of the basic development 

model. A realistic optimum penstock length and 

location on the stream reach was determined for 

each site and followed by the determination of a 

working flow rate. The combination of working 

hydraulic head corresponding to the optimum 

penstock and the working flow rate provided the 

estimate of true hydropower potential power. The 

term “hydropower potential” is used to denote the 

power potential of a site with the development 

constraints applied as opposed to “gross 

potential,” which denotes a site’s power potential 

based solely on the associated stream reach flow 

rate and difference in the elevations at the 

upstream and downstream ends of the reach (gross 

hydraulic head). In either case, the power value is 

9 
 

 

annual mean power, which is directly convertible 

to annual generation, as opposed to the design 

capacity of the plant. 

3.2.1 Project Penstock Length 

The methodology for determining penstock 

lengths for water energy resource sites in a region 

involved several steps: 

Step 1: Penstock lengths of existing low power 

and small hydro plants (FERC 1998) located in the 

region were reviewed to gain an understanding of 

realistic lengths.b

 This review was used to 

establish upper limits for penstock lengths for low 

power and small hydro plants, respectively. 

Step 2: The location on the stream reach 

where the maximum elevation difference was 

obtained using the upper limits of the low power, 

and small hydro penstock lengths or the reach 

length were established. 

Step 3: Beginning with penstock lengths on 

the order of 30 m long, the optimal locations of 

penstocks of successive lengths up to the 

maximums were determined; each providing a 

corresponding hydraulic head. 

Step 4: The optimum low power penstock and 

small hydro penstock lengths and their locations 

on the stream reach were identified as being those 

of the shortest length that captured 90% of the 

hydraulic head captured by using the respective 

upper limit penstocks optimally located on the 

reach. At this point in the hydropower potential 

estimation, it was not known whether the site was 

a low power or small hydro site based on its 

hydropower potential, because the working flow 

rate for the site had not been established. 

only at the beginning and ending nodes of the 

reach. In these datasets, elevation data were 

available at every vertex along the reach. Because 

most of the synthetic hydrography was derived 

using 30-m digital elevation models, this meant 

that elevations were available every 30 or 42 m 

along the reach. 

For the upper limit penstock lengths 

determined based on a regional plant population 

(Step 2 above), the optimal locations of penstocks 

of these lengths were determined by applying 

these lengths starting at successive nodes. The 

location yielding the maximum hydraulic head 

was the optimal location. When searching for the 

optimal penstock location and length (Steps 3 and 

4 above), the location and corresponding hydraulic 

head of penstocks composed of every combination 

of contiguous nodes on the stream reach were 

evaluated up to the penstock length limits. The 

optimal low power and small hydro penstocks at a 

site were those combinations of location and 

minimum length that provided 90% of the 

hydraulic head obtained by optimal placement of 

penstocks having the low power and small hydro 

upper limit lengths. 

The Pacific Northwest Region (HUC 17) is 

used to illustrate how upper limit low power and 

small hydro penstock lengths were determined. 

Penstock lengths for low power plants in the 

region are shown in Figure 4. The figure shows 

there are a large number of plants having penstock 

lengths less than 5,000 ft with the remainder 

having penstock lengths, ranging from 5,000 to 

21,000 ft. The plants with the longer penstocks are 

most likely conduit installations associated with 

25,000 

5,000 

10,000 

15,000 

20,000 

0 

Penstock Length (ft) 

The determination of optimal penstock 

locations and lengths required specialized, 

regional datasets from the Elevation Derivative for 

National Applications (EDNA), which was 

provided by the Earth Resources Observation 

System (EROS) Data Center. In these datasets, the 

elevation annotation of the synthetic stream 0 200 400 600 800 1000 

reaches was expanded beyond having elevations Annual Average Power (kWa) 

Figure 4. Penstock lengths of low power b. Plants having “Conduit Types” in the HPRA Database of 

Canal, Concrete Flume, Pipeline and/or Conduit, and Other hydroelectric plants in the Pacific Northwest 

were not included. Region. 

10 
water delivery systems and are not typical for the 30,000 

natural stream installations, which are the subject 25,000 

of this study. It is also noteworthy that there is no 20,000 Penstock Length (ft) 

correlation of penstock length with plant annual 

15,000 

10,000 

average power. 

The number of plants having penstocks in 

5,000 1,000-ft intervals ranging from 1,000 to 22,000 ft 

is shown in Figure 5. The figure also includes the 

cumulative percentage of plants having penstocks 

of a given length or less. There is a rapid rise in 

the percentage of the sample plant population as 

penstock length increases up to a penstock length 

of 4,000 ft. Eighty percent of the low power plants 

have penstocks of this length or less. For this 

0 

1,000 6,000 11,000 16,000 21,000 26,000 

Annual Average Power (kWa) 

Figure 6. Penstock lengths of small hydroelectric 

plants in the Pacific Northwest Region. 

25 100.0 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 

Number of Plants 

Cumulative Percentage 

90.0 reason, the upper limit of penstocks for potential 20 80.0 

Cumulative Percentage 

Number of Plants

low power projects in Region 17 was chosen to be 70.0 

15 60.0 4,000 ft. 50.0 

40.0 

30.0 

10 

50 100.0 

45 90.0 

Number of Plants 

Cumulative Percentage 

1 2 3 4 5 6 7 8 9 10111213141516 171819202122 

Penstock Length (1,000 ft) 

5 20.0 

Cumulative Percentage 

40 80.0 10.0 

Number of Plants 35 70.0 0 0.0 30 60.0 

25 

20 

15 

50.0 

40.0 

30.0 

Penstock Length (1,000 ft) 

Figure 7. Number of small hydroelectric plants in 10 20.0 

5 10.0 

0 0.0 

Figure 5. Number of low power hydroelectric 

plants in the Pacific Northwest Region by 

penstock length interval and cumulative 

percentage of plants having penstocks of a given 

length or shorter. 

Penstock lengths for a sample of small 

hydropower plants in the region varied similarly to 

those for low power plants as shown in Figure 6. 

Most of the plants in this power class had 

penstocks less than 10,000 ft long with the 

remainder having penstock lengths ranging from 

10,000 to 28,000 ft. 

The number of plants having penstocks in 

1,000-ft intervals ranging from 1,000 to 22,000 ft 

is shown in Figure 7 along with the cumulative 

percentage of plants having penstocks of a given 

length or less. Significant increases in the 

cumulative percentage of plants having penstocks 

of a given length or less occur up to a penstock 

length of 8,000 ft. Nearly 95% of the small hydro 

plants have penstocks of this length or less. For 

this reason, the upper limit of penstocks for 

potential small hydro projects in Region 17 was 

chosen to be 8,000 ft. 

the Pacific Northwest Region by penstock length 

interval and cumulative percentage of plants 

having penstocks of a given length or shorter. 

Similar evaluations of the penstock lengths of 

low power and small hydro plants were carried out 

for each of the regions for which data were 

available. Upper limit penstock lengths for regions 

for which data were not available were determined 

based on values in neighboring regions 

considering topography, climate, and hydrology 

similarities and differences. Figure 8 shows the 

upper limit penstock lengths by region that are 

also given in Table 2 along with the rationale for 

assumed values. 

The choice of whether the low power or small 

hydro penstock applied to the site was determined 

by the logic described in Subsection 3.3. This 

choice was dependent on the applicable working 

flow rate. 

An interesting feature of the data shown in 

Figure 8 and presented in Table 2 is that while the 

penstocks of most of the low power plants are 

shorter than those of small hydro plants for regions 

on the East and West coasts, the relationship is 

11 
12 

LP – 4,000 ft 

SH – 8,000 ft 

LP – 10,000 ft 

SH – 6,000 ft 

LP – 10,000 ft 

SH – 15,000 ft 

LP – 13,000 ft 

SH – 4,000 ft 

LP – 4,000 ft 

SH – 2,000 ft 

LP – 2,000 ft 

SH – 2,000 ft 

LP – 3,000 ft 

SH – 3,000 ft 

LP – 1,000 ft 

SH – 2,000 ft 

S

LP – 8,000 ft 

SH – 11,000 ft 

LP – 10,000 ft 

SH – 15,000 ft 

LP – 3,000 ft 

SH – 2,000 ft 

LP – 3,000 ft 

SH – 2,000 ft 

LP – 300 ft 

SH – 1,000 ft 

LP – 4,000 ft 

SH – 3,000 ft 

LP – 5,000 ft 

SH – 2,000 ft 

LP – 1,000 ft 

SH – 2,000 ft 

LP – 300 ft 

SH – 1,000 ft 

N

a

Figure 8. Penstock length upper limits for low power and small hydro plants in 20 U.S. hydrologic regions. 
Table 2. Penstock upper limits for low power and small hydro plants by hydrologic region. 

Note: Values highlighted in yellow indicate assumed values based on values in another region or regions 

selected using the rationale stated. 

reversed for mid-West and Southwest regions. The 

former situation follows intuitive understanding 

that the higher power small hydro plants would 

require higher hydraulic heads and, therefore, 

longer penstocks. The reverse situation may be the 

result of insufficient data. It could also be the 

result of low power plants being sited on streams 

with relatively small flow rates, thus requiring 

long penstocks to obtain sufficient hydraulic head. 

Conversely, the small hydro plants in these regions 

tend to be located on the larger streams; therefore, 

being capable of producing more power without 

the need for long penstocks. 

3.2.2 Project Working Flow Rate 

Limitations were placed on working flow rates 

to estimate the hydropower potential of sites. The 

working flow rate was limited to the lesser of: 

•	 Half the annual mean flow rate of the stream 

reach associated with the site 

•	 The flow rate required to produce an annual 

average power of 30 MWA using the 

hydraulic head corresponding to the optimal 

small hydro penstock length and location. 

In most cases, if the working flow rate was less 

than half the reach flow rate, it was because half 

the reach flow rate in combination with the 

hydraulic head corresponding to the optimal small 

hydro penstock for the site resulted in a 

hydropower potential greater than 30 MWA. 

Because this development of the site would no 

longer produce a small hydro plant, the flow rate 

was restricted so that the project hydropower 

potential would be 30 MWA. However, there were 

instances in Regions 10 through 16 where the 

working flow rate was reduced to less than half the 

reach flow rate even for low power projects as will 

be discussed in the next subsection. 

3.2.3 Logic for Selecting Site 

Development Parameters 

A logic scheme was used to determine 

whether a site would be developed as a low power 

or small hydro project. Optimal low power and 

small hydro penstock lengths and locations were 

determined as described in Subsection 3.2.1. 

Working flow limitations were adopted as 

described in the previous subsection. This 

information was combined to determine the power 

class of the project and associated development 

13 
parameters. The logic for this process is shown in 

Figure 9. The basic approach was first to try and 

develop the site as a small hydro project using half 

the reach flow rate and the optimal small hydro 

penstock for the site. This either resulted in 

reduction of the working flow rate to limit the 

project to being a small hydropower project, 

confirmation that the project could be developed 

as a small hydro project, or determination that 

there was not sufficient hydropower potential at 

the site, indicating a low power project 

development. If a low power project development 

was indicated, the only remaining step was to 

resolve an ambiguity that occurred in Regions 10 

through 16. In these regions, it was possible for 

the optimum low power penstock for a site to be 

longer and, therefore, have more corresponding 

hydraulic head than the optimum small hydro 

penstock. It was thus possible to have the working 

flow rate equal to half the reach flow rate in 

combination with the small hydro penstock 

indicate a low power project and yet the working 

flow rate in combination with the low power 

penstock indicate a small hydro project. This 

ambiguity was resolved by arbitrarily reducing the 

working flow rate in combination with the 

optimum low power penstock and corresponding 

hydraulic head such that hydropower potential of 

the project was slightly less than 1 MWA, 

ensuring that it was a low power project. This 

approach was taken as opposed to reducing the 

low power penstock length to take the most 

conservative approach with regard to use of the 

stream resource. 

with longest, typical penstock length 

based on existing small hydro plants in the 

region. 

•	 Flow rate—lesser of: 

– Half the stream reach flow rate 

– Flow rate required to produce an annual 

average power of 30 MWa using hydraulic 

head corresponding to optimal small 

hydro penstock. 

These assumptions are conservative for some 

sites for one or a combination of reasons. It was 

assumed that the penstock paralleled the stream 

for all projects. Depending on the topography and 

the stream path, it may be possible to capture more 

of the reach hydraulic head if the penstock is run 

transverse rather than parallel to the stream if it 

has a serpentine path. There may be instances in 

which more of stream flow can be used for power 

production than dictated by the development 

criteria. Flow rates have also been limited to that 

required to produce 30 MWa because of the focus 

of this study. Larger working flows and 

subsequently larger hydropower potentials exist at 

some sites and may be available for development. 

Finally, the hydropower model that has been used 

in this study is a potential energy conversion 

model. If a kinetic energy model consisting of one 

or a group of kinetic turbines had been applied to 

stream reaches having little power potential by 

virtue of little hydraulic head, but having adequate 

stream velocities, significant additional 

hydropower potential may well have been 

identified. 

3.2.4 Summary of Site Development 

Criteria for Estimating Project 

Hydropower Potential 

The site development criteria that were used to 

estimate project hydropower potential were: 

•	 Project location—optimal based on hydraulic 

head capture 

•	 Penstock length 

– Low power project—optimal based on 

capturing 90% of hydraulic head captured 

with longest, typical penstock length 

based on existing low power plants in the 

region 

– Small hydro project—optimal based on 

capturing 90% of hydraulic head captured 

3.3 Project Feasibility Criteria 

The project feasibility criteria that were used 

to identify feasible potential project sites 

addressed the likelihood of development based on 

land use and environmental sensitivities, prior 

development, site access, and load and 

transmission proximity. Specifically, the 

feasibility criteria applied to each water energy 

resource site were: 

•	 Hydropower potential ≥10 kWa 

•	 Does not lie within a zone in which 

development is excluded by federal law or 

policy 

14 
Working Flow Rate 

15 

Hydropower Potential > 30 MWa?

YES

NO

SMALL HYDRO PROJECT

• Small hydro penstock• Working flow rate = flow rate required to

produce 30 MWa

Hydropower Po

SMALL HY

• Small hydro pen• Working flow ra

Assumed Equal to

Half Stream Reach 

Flow Rate

Optimal Small Hydro

Penstock Assumed

with Corresponding 

Hydraulic Head

Compute

Site Hydropower Potential

(MWa)

Working Flow Rate 

Assumed Equal to

Half Stream Reach 

Flow Rate

Optimal Low Power

Penstock Assumed

with Corresponding 

Hydraulic Head

Compute

Site Hydropower Potential

(MWa)

Hydropower Potential < 1 MWa?

YES

NO

LOW 

• Low power • Working flo

produce 1 M

Hydropower Potential > 30 MWa?

YES

Hydropower Potential > 30 MWa? NO

YES 

NO 

SMALL HYDRO PROJECT 

• Small hydro penstock • Working flow rate = flow rate required to 

produce 30 MWa 

Hydropower PoHydropower Po

SMALL HY

• Small hydro pen• Working flow ra

Assumed Equal to 

Half Stream Reach 

Flow Rate 

Optimal Small Hydro 

Penstock Assumed 

with Corresponding 

Hydraulic Head 

Compute 

Site Hydropower Potential 

(MWa) 

Working Flow Rate 

Assumed Equal to 

Half Stream Reach 

Flow Rate 

Optimal Low Power 

Penstock Assumed 

with Corresponding 

Hydraulic Head 

Compute 

Site Hydropower Potential 

(MWa) 

Hydropower Potential < 1 MWa?

YES

Hydropower Potential < 1 MWa? NO

YES 

NO 

LOW 

• Low power • Working flo

produce 1 M

LOW PP OWER PROJECT 

• Low pow pow er penstock • Working flow rate = rate = half of r of r each flow rate 

Figure 9. Logic for determining whether a water energy resource site should be developed as a low power or small hydro pdevelopment criteria thereby establishing working flow rate, penstock length, working hydraulic head, and hydropower pot
 

•	 Does not lie within a zone that makes 

development highly unlikely because of land 

use designations 

•	 Does not coincide with an existing 

hydroelectric plant 

•	 Is within 1 mile of a road 

•	 Is within 1 mile of part of the power 

infrastructure (power plant, power line, or 

substation) OR is within a typical distance 

from a populated area for plants of the same 

power class in the region. 

The question of whether site development was 

highly unlikely due to federal land use designation 

or environmental sensitivities was answered by 

intersecting the stream reaches corresponding to 

water energy resource sites with the polygons 

corresponding to the exclusion zones using GIS 

tools. (Descriptions of the exclusion zones used in 

this study are provided in Appendix A.) If any 

point on the reach fell within the exclusion zone, 

site development was considered to be unfeasible. 

On the other hand, a site could be very close to the 

exclusion zone boundary and not be disqualified 

based on the exclusion criterion (all parts of 

stream reach outside the boundary). 

Sites that have already been developed into a 

hydroelectric plant were identified using a 2-mile 

search radius from the plant location to identify 

the water energy resource site that most nearly 

matched the head and annual average power of the 

plant. A search radius of this size was required, 

because it was found that some plant locations 

based on their geographic coordinates differed by 

this much and sometimes more from their obvious 

location at the head of a reservoir. Only 

hydroelectric plant locations were used, so it is 

possible that an existing dam without a power 

house is located at the feasible project site. 

Hydroelectric plant locations were provided by by 

a combination of locations in the HPRA Database 

(FERC 1998), locations in ENERmap’s power 

system data layer (ENERmap 2005), and manual 

corrections by matching plant locations to water 

features using GIS tools. 

The accessibility criterion of the site being 

within 1 mile of a road was chosen because it was 

reasoned that particularly a low power 

hydroelectric project could not afford construction 

of a road longer than 1 mile and be economically 

viable. This criterion was not found to be very 

restrictive, because proximity analysis revealed 

that 84% of the available resource sites were 

within 1 mile of a road. The ESRI Streetmap 

(ESRI 2004) GIS layer of roads was used in the 

proximity analysis. 

The feasibility criterion for proximity to a part 

of the power infrastructure was also chosen to be 

1 mile considering low power project funding 

constraints to construct a powerline to connect to 

existing power infrastructure. The feasibility 

analysis did not account for the voltage of the 

nearby powerlines or consider the affordability of 

the transformer required to connect the potential 

project to the grid. The power infrastructure was 

geographically represented by geospatical data 

provided by ENERmap, LLC (ENERmap 2005). 

The feasibility criterion for proximity to cities 

and population centers was based on the distance 

of most of the existing hydroelectric plants in each 

power class (low power or small hydro) to a city 

or population center. Two GIS layers were 

required for this part of the proximity analysis. It 

was found that very small towns were best 

represented by a discrete city location. Larger 

populated areas were best represented by polygons 

corresponding to the boundary of the populated 

area. The feasibility criterion in this case was 

based on actual locations of hydroelectric plants 

rather than an assumed economic limitation as 

with the construction of an access road or hook up 

to a transmission line. It was reasoned that 

municipalities have local electrical lines extending 

beyond their boundaries that have made low 

power and small hydropower projects viable at 

some distance from the densely populated area. 

These lower voltage electrical lines were generally 

not represented in the electrical transmission GIS 

layer used in the analysis. 

The distribution of low power and small 

hydroelectric plants to populated areas in the 

Pacific Northwest Region shown in Figure 10 is 

typical of most of the regions. The distributions 

for low power and small hydroelectric plants 

considered separately were sufficiently similar to 

the combined distribution shown in Figure 10 

making it unnecessary to define separate criteria 

16 
 

 

0 

10 

20 

30 

40 

50 

60 

70 

for each power class. For this region, the 

distributions show that 90% of the low power and 

small hydro plants were within 10 miles of a city 

center or population center boundary. 

The distances that 90% of the low power and 

small hydro plants are from a city or populated 

area boundary are shown in Table 3 for each of the 

20 hydrologic regions. Application of the criterion 

for proximity to a city or populated area required 

knowing whether a water energy resource site 

would be developed as a low power or small hydro 

plant so that the correct proximity criterion could 

potential assessment and the proximity analyses 

were entered into an Access database containing 

the attribute data for all water energy resource 

sites. The attributes used in the feasibility 

assessment are listed in Table 5.c

 Queries on the 

database implementing the feasibility criteria 

resulted in identification of water energy resource 

sites that are the sites of feasible potential projects. 

Table 3. Distances of 90% of low power and small 

hydro plants from cities and populated area 

boundaries in 20 hydrologic regions. 

be used. It is for this reason that the hydropower 

potential and thus power class of each water 

energy resource site, if it was developed, was 

evaluated as described in Subsection 3.2 prior to 

the feasibility evaluation using the criteria 

described in this subsection. 

3.4 Identification of Feasible 

Potential Projects 

Evaluation of the water energy resource sites 

using the feasibility criteria described in the 

previous subsection required the water energy 

resource sites to be attributed with proximity data 

for each of the parameters addressed in the 

feasibility criteria. Proximity analyses were 

performed using GIS tools and the GIS data layers 

listed in Table 4. The results of the hydropower 

80 110 

Region 

Low Power 

Plant 

Distance in 

Miles 

Small Hydro 

Plant 

Distance in 

Miles 

1 4 4 

2 5 5 

3 5 5 

4 4 7 

5 2 6 

6 5 5 

7 4 4 

8 4 4 

9 1 1 

10 7 7 

11 7 4 

12 3 8 

13 4 4 

14 7 7 

15 5 10 

16 6 4 

17 10 10 

18 8 8 

19 10 10 

20 2 2

Cumulative Percentage of Plants

Total Number of Plants = 280 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 

Distance from Population Center (miles) 

Lo w P o wer 

Small H ydro 

Lo w P o wer & Sma ll H ydro 90% of plants less than10 mi. 

100 

90 

80 

70 

60 

50 

40 

30 

20 

10 

0 

Number of Plants 

0 1 2 3 	 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 

Distance from Population Center (miles) 

(a) (b) 

Figure 10. a) Distribution of the distance of low power and small hydroelectric plants to a city or 

population center boundary. b) Cumulative distribution of the distance of low power and small 

hydroelectric plants to a city or population center boundary. 

c. The attributes listed in Table 5 are only those that were required to perform the feasibility assessment to identify feasible 

potential projects. 

17 
 

 

 

 

 

Table 4. GIS data layers used for proximity analyses. 

Feature Source 

Data 

Vintage Source Website 

Federal Exclusion 

Zones 

National Atlas of the United 

States 

Federal & Indian Lands 

Parkways & Scenic Rivers 

2002 http://nationalatlas.gov/natlas/Natlass 

tart.asp 

Environmental 

Exclusion Zones Conservation Biology Institute 2005 http://www.consbio.org/ 

Roads 

Environmental Systems 

Research Institute (ESRI) 

(Streetmap) 

2004 http://www.esri.com/data/index.h 

tml 

Power Infrastructure Global Energy Decisions 2004 http://www.globalenergy.com/

 Transmission lines 

 Substations 

 Power plants 

Cities 

Environmental Systems 

Research Institute (ESRI) 

(cities_dtl) 

2000 http://www.esri.com/data/index.html 

Populated Places 

Environmental Systems 

Research Institute (ESRI) 

(placeply) 

2000 http://www.esri.com/data/index.html 

Table 5. Water energy resource site attributes used in development feasibility assessment. 

Name Description Units 

PEN_POWER_KW Hydropower potential kWa 

PEN_TECH Technology classification (LP or SH) 

FED_EXCLUDED Stream reach intersects federal exclusion area (Y = yes, N = no) 

GAP_EXCLUDED 1 

Stream reach intersects a GAP area with GAP value of 1 or 2 (Y = yes, N = 

no) 

DEVELOPED 

Stream reach is likely the site of an existing hydroelectric plant (Y = yes, N 

= no) 

ROAD_DIST_M Distance to nearest road. m 

PLANT_DIST_M Distance to nearest existing power plant. m 

SUBST_DIST_M 2 Distance to nearest substation. m 

PWRLN_DIST_M 1 Distance to nearest power line. m 

POP_DIST_M Distance to boundary of nearest populated area or city center. m 

Note 1: Data not available for Hawaii. 

Note 2: Data not available for Alaska and Hawaii. 

18 
Feasible Potential

4. RESULTS 

The discussion of results begins with an 

overview of the water energy resource site 

population that was assessed to identify feasible 

potential projects. This overview is followed by a 

discussion of the feasibility assessment results for 

the country presented in terms of numbers of 

feasible potential projects and their corresponding 

hydropower potential divided into power classes 

and into project size as designated by ranges of 

power potential. The results are then discussed 

from the perspective of their spatial distribution 

across the country by comparing results for each 

state and viewing the potential projects on a map. 

The last subsection discusses how the reader can 

access additional information about potential 

projects using a GIS application on the Internet 

called the VHP. 

Developed Sites 

1,961 Excluded Sites Feasible Sites 0% 88,383 127,758 18% 

4.1 Power Category 

Distribution of Assessed 

Water Energy Resource Site 

Population 

The water energy resource site population on 

which the feasibility assessment was performed 

included 500,157 sites representing a total gross 

power potential of 297,436 MWa. The distribution 

of these sites and their associated gross power 

potential on the basis of four categories: 

• Developed 

• Excluded 

• Feasible 

• Other available. 

is shown in Figure 11. This figure shows that 

127,758 sites having a total gross power potential 

26% 

Other Available Sites 

282,055 

56% 

Total Resource Sites 

Developed Potential 

24,084 MWa 

500,157 8% 

Excluded Potential 

97,845 MWa 

33% 

98,700 MWa 

33% 

Other Available 

Potential 

76,807 MWa
 

26%
 

Total Resource Potential 

297,436 MWa 

Figure 11. Power category distribution of water energy resource sites having gross power potentials 

greater than or equal to 10 kWa and their associated total gross power potential. 

19 
 

of 98,700 MWa were identified by the feasibility 

assessment as being sites for feasible potential 

projects. These sites constitute 26% of the site 

population and 33% of the total gross power, 

respectively. 

The total power and its distribution shown in 

Figure 11 differ somewhat from results reported 

from the predecessor study (Hall et al. 2004). The 

total resource potential of 297,436 MWa is 

approximately 8,000 MWa higher than previously 

reported. This is the result of data refinements in 

the basic reach used in present study. The amount 

of excluded power increased in the present study 

by approximately 9,000 MWa because of the 

inclusion of environmentally sensitive areas, 

which added to the total area of zones in which 

hydropower development is unlikely. The amount 

of developed potential reported in the present 

study is approximately 10,000 MWa less than in 

the previous study. The methods of obtaining this 

value were different in the two studies. In the 

previous study, total average power for the U.S. 

hydroelectric plant population was used. This 

value was derived using the estimated average 

annual generation of each plant in the HPRA 

Database (FERC 1998), dividing this generation 

by the number of hours in a year to obtain plant 

average power, and summing all the plant values. 

In the present study, developed potential was 

determined by spatially relating water energy 

resource sites with existing hydroelectric plants, 

thereby identifying the gross power potential of 

sites corresponding to plant locations as developed 

potential. 

Both methods of identifying developed 

potential have significant uncertainties. The 

estimated average annual generation in the HPRA 

Database is taken from the plant license 

application, if these data are provided. The value is 

the licensee’s estimate of annual average 

generation at the time of application. Actual 

annual average generation could differ 

significantly over the period from when the 

application was filed to the present. If the average 

annual generation is not provided in the 

application, the value entered in the database is 

calculated from the nameplate capacity, assuming 

a capacity factor of 1.0 — clearly an 

overestimation. 

The uncertainty in developed potential derived 

in the present study stems from at least two known 

sources. Identifying water energy resource sites as 

developed based on collocation with a 

hydroelectric plant depends on having accurate 

plant geographic coordinates. It was found in 

many cases that these coordinates were not 

sufficiently accurate for this purpose. Large plant 

locations were manually verified to the extent 

possible using GIS tools to ensure the plant 

location was on a stream or located at the head of 

a reservoir. Still a search radius had to be used, 

and the nearest stream reach whose gross power 

potential and hydraulic head most closely matched 

the plant average power (derived from estimated 

average annual generation as stated above) and 

hydraulic head was considered the corresponding 

developed site and its potential the developed 

potential. It was also possible to miss developed 

potential for plants having reservoirs that extended 

for many miles upstream. These plants take 

advantage of elevation change occurring over 

miles of stream path, concentrating this elevation 

change at the dam to produce localized hydraulic 

head. Ideally, the existence of the reservoir is 

captured in the digital elevation model (DEM) that 

was used to derive the synthetic hydrography, 

which provided the hydraulic head and 

consequently the gross power potential for a water 

energy site in our study. If the presence of the 

reservoir is included in the DEM, a synthetic 

stream reach will have the local elevation change 

at the dam. However, if the DEM does not reflect 

the presence of the reservoir or its full extent, but 

rather reflects the topography underlying the 

reservoir, some of the upstream stream reaches 

that should have been flagged developed will be 

missed and thus reduce the total developed 

potential. Considering the uncertainties in both 

methods, it is best to consider values from the two 

methods as upper and lower bounds of the 

developed potential. In a worst case, the total 

available potential (feasible and other available) of 

175,507 MWa would be reduced by 10,000 MWa. 

20 
 

d

 

4.2 Power and Technologies 

Class Distribution of 

Feasible Potential Projects 

The nearly 130,000 feasible potential projects 

identified in the study were classified as either low 

power (hydropower potential less than 1 MWa) or 

small hydro (hydropower potential greater than or 

equal to 1 MWa, but less than or equal to 

30 MWa). The low power projects were further 

subdivided using the operating envelopes of 

classes of low power technologies shown in 

Figure 12. The hydropower potential and working 

hydraulic head of the potential project were used 

to assign technologies class. The unconventional 

systems class of technologies, which is delineated 

by the working hydraulic head being less than 8 ft, 

is intended to show that if the potential is going to 

be realized, it will require the use of an ultra low 

head turbine or hydrokinetic technology. It is not 

known from the assessment performed whether 

there is sufficient velocity at the site to make a 

hydrokinetic installation viable. 

The power potential of U.S. water energy 

resource sites is presented in power categories and 

is divided by power classes and classes of low 

power hydropower technologies in Table 6. The 

power values listed for the power categories 

“Total” through “Feasible” are total gross power 

potential values for a group of water energy 

resource sites. The values listed for each power 

category “Developed” through “Feasible” for a 

particular power classd

 (e.g., “Small Hydro”) 

correspond to a subset of the water energy 

resource sites whose total gross power potential is 

listed under the “Total” power category. The sites 

corresponding to the values listed in the “Feasible” 

category are a subset of those corresponding to the 

values listed under the “Available” category. 

The power values listed under “Potential 

Projects” are hydropower potential values. They 

Figure 12. Operating envelopes of three classes of low power technologies. 

d. The low power technology classes were assigned to water energy resource sites and their cumulative power potential by using 

the operating envelopes shown in Figure 12, but were based on reach hydraulic head and full flow rate rather than working 

hydraulic head and flow rate, which were used to classify low power potential projects. 

21 
Feasible Projects

127,758

Microhydro

93,821

73%

Unconventional 

Systems

6,032

5%

Conventional 

Turbines

22,485

18%

Small Hydro

5,420

4%

Feasible Project Hydropower Potential

29,438 MWa

Conventional 

Turbines

6,297 MWa

21%

Microhydro

3,052 MWa

10%

Unconventional 

Systems

1,640 MWa

6%

Small Hydro

18,450 MWa

63%

Table 6. Power potential of U.S. water energy resource sites in power categories divided into power 

classes and low power technology classes. 

do not correspond to a subset of the water energy 

resource sites reflected in the “Total” power 

category for a given power or technology class. 

This is because application of the development 

criteria produced hydropower potential values that 

were significantly less than the gross power 

values. Thus, water energy resource sites that were 

power classed based on their gross power potential 

were not necessarily in the same power class based 

on their hydropower potential. For example, all the 

Small Hydro Conventional 

5,420 Turbines 

4% 22,485 

18% 

sites that were classed as “Large Hydro” based on 

their gross potential became “Small Hydro” or 

“Low Power” potential projects. 

The distribution of feasible potential project 

sites and their associated hydropower potential is 

shown in Figure 13. This figure shows the results 

of applying the development criteria to obtain 

better estimates of hydropower potential. The 

nearly 130,000 feasible project sites, which had a 

total gross power potential of nearly 

Unconventional 

Systems 

6,032 

5% 

93,821 Unconventional Microhydro 

73% Systems 3,052 MWa 

1,640 MWa 10% 

Feasible Projects 

127,758 

Conventional 

Turbines 

6,297 MWa 

21% 

Microhydro 

6% 

Small Hydro 

18,450 MWa 

63% 

Feasible Project Hydropower Potential 

29,438 MWa 

Figure 13. Power category distribution of feasible potential projects and their associated total hydropower 

potential with low power projects further divided by low power technology classes. 

22 
100,000 MWa, were found to realistically offer 

30,000 MWa of hydropower potential. This is not 

surprising considering that the development 

criteria of using half the site’s flow or less resulted 

in at least halving of the possible amount of 

hydropower potential compared to the gross power 

potential. The working flow rate restriction may be 

overly conservative resulting in more total 

hydropower potential than that estimated by the 

study. The methodology used in the study also did 

not explicitly evaluate hydrokinetic potential at 

sites where there may be little or no elevation 

difference, but sufficient velocity and stream depth 

to support energy extraction using hydrokinetic 

technologies. 

It is essential that the total hydropower 

potential of approximately 30,000 MWa not be 

interpreted to be same as 30,000 MW of likely 

capacity increase potential identified in a sitebased resource assessment conducted during the 

1990s by INL (Connor et al. 1998). While the 

numerical values are the same, the units and 

associated generation potential are not. The 

hydropower potential estimated by the present 

study is annual mean power. This power value 

translates directly to generation power when 

multiplied by the number of hours in a year 

(8760 hr). In contrast, the total capacity increase 

potential identified in the prior study requires the 

application of a capacity factor to estimate the 

corresponding potential generation. Considering 

that the average capacity factor for the U.S. plant 

population is 50%, the capacity increase potential 

corresponds to a 15,000-MWa increase when 

viewed as annual average power. Conversely, the 

30,000 MWa identified in the present study could 

imply a 60,000-MW increase in capacity. It is not 

anticipated that this large an increase in capacity 

would be required in light of the development 

assumption of only using part of the stream flow, 

which would allow the identified potential projects 

to operate at higher capacity factors. 

The information shown in Figure 13 is put in 

perspective by comparison with information about 

the present U.S. plant population shown in 

Figure 2. The 30,000 MWa of hydropower 

potential estimated by this study is comparable to 

the total average power of the existing plant 

population, which is between 25,000 and 

35,000 MWa as discussed above. However, 

considering that the present plant population 

numbers on the order of 2,400 plants (not counting 

pumped storage plants), it is clear that 

130,000 projects will not get built in the 

foreseeable future, which would double U.S. 

annual hydropower generation. The fact that the 

study identified this many feasible projects does 

indicate a significant number of opportunities for 

new hydropower development. Development that 

is more realistic is represented by the 5,400 new 

small hydro projects identified by the study as 

shown in Figure 13. These potential projects 

represent nearly 20,000 MWa of hydropower 

potential, which would increase in U.S. annual 

hydropower generation by more than 50%, if they 

were developed. 

The distribution of potential low power 

projects on the basis of the number of projects and 

their corresponding hydropower potential in 

100-kWa bins ranging from 100 to 1,000 kWa is 

shown in Figure 14. Most of the 122,338 potential 

projects in this power class are microhydro 

projects (hydropower potential less than 100 kWa) 

3,500 100,000 

90,000 

93,821 Low Power Potential Projects 

122,338 

13,681 

5,819 3,181 2,025 1,403 978 651 479 300 

3,052 

Total Hydropower Potential 

10,988 MWa 

1,935 

1,420 

1,102 

905 

631 

767 

487 406 

284 

3,000 

80,000 

70,000 

60,000 

50,000 

40,000 

30,000 

Group Hydropower Potential (MWa) 

Number of Potential Projects 

2,500 

2,000 

1,500 

1,000 

20,000 

10,000 

500 

0 

100 200 300 400 500 600 700 800 900 1,000 100 200 300 400 500 600 700 800 900 1,000 

Hydropower Potential (kWa) Hydropower Potential (kWa) 

(a) (b) 

Figure 14. Distribution of (a) number and (b) group hydropower potential of U.S. low power potential 

projects. 

23 

0 
representing approximately 30% of the total 

hydropower potential for this class of potential 

projects. The remaining 28,517 potential projects 

representing approximately 8,000 MWa of 

hydropower potential have power potentials 

between 100 and 1000 kWa. 

Similar distributions for small hydro potential 

projects are shown in Figure 15 in which the bins 

are 2 MWa, ranging from 2 to 30 MWa. Again, 

the potential projects at the lower end of the power 

class constitute most of the population. There are 

4,375 potential small hydro projects or 80% of the 

population having hydropower potentials in the 

range from 1 to 4 MWa. These projects represent 

slightly over 40% of the total small hydro 

hydropower potential. The remaining hydropower 

potential of 13,000 MWa corresponds to 

1,045 potential projects ranging from 6 to 

30 MWa. At the upper end of the power class, 

78 potential projects having hydropower potentials 

between 28 and 30 MWa represent a total 

hydropower potential of 2,330 MWa. Most of 

these projects correspond to using just enough 

flow rate to produce 30 MWa from larger streams 

where use of half the flow rate would result in 

development of a large hydro class project. The 

approximately 5,000 potential small hydro projects 

identified in the study represent the group of 

projects that would most efficiently increase U.S. 

hydropower generation. 

Small Hydro Potential Projects 

5,420 3,006 

1,369 

422 

212 

90 59 57 25 26 28 17 15 4 12 78 

0 

500 

1,000 

1,500 

2,000 

2,500 

3,000 

3,500 

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 

Hydropower Potential (MWa) 

Number of Potential Projects 

(a) 

4.3 Spatial Distribution of Water 

Energy Resources and 

Potential Projects 

The total gross power potential of water 

energy resource sites in each of the 50 states of the 

United States is shown in Figure 16. The total state 

gross power potential is divided into the potential 

that could feasibly be developed, other available 

potential that has not been developed and is not 

excluded from development, potential that is 

excluded from development either because it is in 

a zone where federal land use or environmental 

sensitivity make development unlikely, and 

potential that has already been developed 

corresponding to existing hydroelectric plants. 

This figure shows that six western states, Alaska, 

Washington, California, Idaho, Oregon, and 

Montana, have significantly more gross power 

potential that the other 44 states. For the vast 

majority of the states (42) the feasible gross 

potential is more than half of the available gross 

potential. The average percentage of available 

gross potential that is feasible is 71%. 

Alaska is outstanding both because of it vast 

power potential (on the order of three times any 

other state) and because its feasible gross potential 

is only 14% of that available. Nearly half of the 

state’s power potential lies within zones where 

development is unlikely. These characteristics of 

the state’s water energy resources are 

understandable in light of its large area, extent of 

mountainous terrain, prevalence of protected 

areas, and remote location of many resources. 

4,500 

4,164 Total Hydropower Potential 

4,000 3,785 

18,450 MWa 

3,500 

3,000 

Wa) tial (M 2,500 Poten

2,330 

er 

2,050 

2,000 

pow 1,500 Group Hydro

1,468 

806 

638 734 

372 440 532 

360 348 

101 

322 

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 

Hydropower Potential (MWa) 

(b) 

1,000 

500 

0 

Figure 15. Distribution of (a) number and (b) group hydropower potential of U.S. small hydro potential 

projects. 

24 
Delaware Rhode Island North Dakota New Jersey Connecticut Florida Massachuse tts Maryland South Dakota Kansas New Hampshire Michigan Iowa Nebraska Vermont Nevada South Carolina Indiana Ohio Oklahoma Minnesota Wisconsin New Mexico Georgia Hawaii Virginia Texas Illinois North Carolina Maine Mississippi Louisiana Alabama Arizona Missouri West Virginia KentuckyUtah Pennsylvania New York Tenne ss ee Arkansas Wyoming Colorado Montana Oregon Idaho California Washington 

25 

35,000 30,000 25,000 20,000 15,000 10,000 

5,000 

0 

Feasible Other Available Excluded Developed 

Annual Mean Power ( MWa) 

Figure 16. Total gross power potential of water energy resources in the 50 states of the United States divided into feasible, excluded, and developed power categories. 
The gross power potential for each state 

shown in Figure 16 can also be viewed from the 

perspective of power density by dividing each 

state’s gross power potential by its planimetric 

area. The result shown in Figure 17 provides an 

indication of the density of water energy resources 

in the state. From this perspective, Washington 

and Hawaii have significantly higher power 

densities than the other 48 states. This is the result 

of high rainfall coupled with significant elevation 

differences in the topography. 

The total hydropower potential of feasible 

potential projects in each of the 50 states of the 

United States is shown in Figure 18. The total 

hydropower potential of each state is divided into 

that corresponding to low power and small hydro 

potential projects. The same six western states that 

were found to have the most gross power potential 

were found to have the most hydropower potential, 

but not in the same order. While Alaska had by far 

the most gross power potential, California was 

found to have the most hydropower potential when 

feasibility is considered. For most states, most of 

the hydropower potential was associated with 

potential small hydro projects (on average 63% of 

the total hydropower potential compared to the 

remaining 37% associated with potential low 

power projects). 

The hydropower potential of feasible potential 

projects in each state is put in perspective by 

comparing to the total average power of the 

existing hydroelectric plants in the state. Table 7 

provides this comparison and shows what 

percentage increase in generation would be 

achieved if all the potential projects identified in 

the state were developed. For this comparison, the 

higher estimates of annual average power derived 

from the estimated annual generation listed in the 

HPRA Database (FERC 1998) were used to be 

conservative. The data in Table 7 show that 

33 states would increase their hydropower 

generation by 100% or more and 41 states would 

increase their generation by more than 50% if all 

the potential projects identified in the state were 

developed. 

As with gross power potential, it is useful to 

know what states have the highest concentrations 

of hydropower potential. This view is provided by 

Figure 19. The same two states, Washington and 

Hawaii, that have outstanding concentrations of 

gross power potential, also have outstanding 

concentrations of hydropower potential, but in 

reverse order. Hawaii has the distinction of having 

the highest concentration of hydropower potential, 

followed closely by Washington. Seven states: 

Idaho, Vermont, California, Oregon, Connecticut, 

Pennsylvania, and West Virginia make up the next 

tier of states having power densities greater than 

20 kWa/sq mi with Idaho being the only one of 

this group that exceeded 25 kWa/sq mi. 

The locations of the 127,758 potential project 

sites are shown on the map in Figure 20. Project 

sites are differentiated by whether they are small 

hydro or low power sites. The low power sites are 

further differentiated by low power technology 

class. The 2,391 existing hydroelectric plants are 

Table 7. Comparison of hydropower potential of feasible potential projects with total annual average 

power of hydroelectric plants in each of the 50 states of the United States. 

State Name 

Developed 

Hydropower 

(MWa) 

Feasible 

Potential 

Hydropower 

(MWa) 

Potential 

Hydropower 

Increase State Name 

Developed 

Hydropower 

(MWa) 

Feasible 

Potential 

Hydropower 

(MWa) 

Potential 

Hydropower 

Increase State Name 

Developed 

Hydropower 

(MWa) 

Feasible 

Potential 

Hydropower 

(MWa) 

Potential 

Hydropower 

Increase 

Delaware 0 6 ∞ Utah 135 401 297% New Hampshire 187 174 93% 

Mississippi 0 298 ∞ Virginia 147 418 284% California 4699 3,425 73% 

Kansas 1 295 29451% Florida 32 79 245% Michigan 209 133 64% 

Illinois 27 568 2103% Nebraska 152 354 233% Oregon 3271 2,072 63% 

Alaska 171 2,694 1575% Connecticut 55 105 191% Tennessee 1082 655 61% 

Hawaii 20 280 1400% Texas 189 328 174% North Carolina 610 348 57% 

New Jersey 6 63 1057% Vermont 128 217 170% Georgia 429 230 54% 

Missouri 129 798 618% Idaho 1288 2,122 165% South Carolina 428 211 49% 

New Mexico 30 156 519% Rhode Island 4 7 163% Maryland 203 91 45% 

Ohio 63 319 506% Arkansas 405 590 146% Alabama 1113 462 41% 

Indiana 67 305 455% Oklahoma 239 345 144% Nevada 263 95 36% 

Wyoming 117 507 433% Montana 1192 1,669 140% Washington 11470 3,106 27% 

Colorado 246 891 362% Kentucky 383 518 135% New York 2861 757 26% 

Iowa 95 329 347% Minnesota 128 140 109% South Dakota 622 119 19% 

West Virginia 140 484 346% Massachusetts 126 136 108% Arizona 928 150 16% 

Louisiana 89 306 343% Maine 432 432 100% North Dakota 270 40 15% 

Pennsylvania 284 953 336% Wisconsin 264 259 98% 

26 
 

North Dakota Florida Texas South Dakota Delaware Kansas Nevada New Mexico Nebraska Minnesota Michigan Oklahoma Iowa Wisconsin Arizona Rhode IslandOhio New Jersey Georgia Indiana Illinois South CarolinaUtah Missouri North Carolina Virginia Mi ssissippi Wyoming Alabama Louisiana Colorado Maryland Massachuse tts Montana Maine Co nnecticut Kentucky New York Pennsylvania Arkansas New Hampshire Vermont Tenness

West V

27 

500 450 400 350 300 250 200 150 100 

50 

0 

Feasible Other Available Excluded Developed 

Annual Mean Power Density (kWa/sq. mi) 

Figure 17. Total gross power potential density of water energy resources in the 50 states of the United States divided into feexcluded, and developed power categories. 
Delaware Rhode Island North Dakota New Jersey Florida Maryland Nevada Co nnecticut South Dakota Michigan Massachusetts Minnesota Arizona New Mexico New Hampshire South Carolina Vermont Georgia Wisconsin Hawa ii Kansas Mi ssissippi Indiana LouisianaOhio Texas Iowa Oklahoma North Carolina NebraskaUtah Virginia Maine Alabama West Virginia Wyoming Kentucky Illinois Arkansas Tennessee New York Missouri Colorad

Pennsyl

28 

0 

500 

1,000 1,500 2,000 2,500 3,000 3,500

A nnua l M e a n P o w e r ( M W a ) 

Small Hydro Low Power 

Figure 18. Total hydropower potential of feasible low power and small hydro projects in the 50 states of the United States. 
 

North Dakota Nevada Texas New Mexico Arizona Florida South Dakota Minnesota Michigan Delaware Kansas Georgia Nebraska Wisconsin AlaskaUtah Oklahoma WyomingIowa Rhode Island Mi ssissippi Louisiana South Carolina North CarolinaOhio Indiana New Jersey Colorado Alabama Maryland Illinois Virginia Arkansas Montana Missouri Kentucky Maine Tennessee New York Massachusetts New Hampshire West Virginia Pennsylva

Co nn

29 

50 45 40 35 30 25 20 15 10 

5 0 

Small HydroLow Power

Annual Mean Power Density (kWa/sq. mi) 

Figure 19. Total hydropower potential density of feasible low power and small hydro projects in the 50 states of the United 
30 
• 

Figure 20. Existing hydroelectric plants and feasible potential hydropower projects in the United States. 

31 

also shown on the map. Figure 20 provides an 

indication of the location of the project sites and 

visual image of their concentration. Every state 

contains some potential project sites. It is clear 

from the map and Figure 19 that eight states, 

North Dakota, Nevada, Texas, New Mexico, 

Arizona, Florida, South Dakota, and Minnesota, 

have notably low concentrations of project sites in 

at least part of the state. Other than these states, 

most states have significant numbers and 

concentrations of potential project sites including 

Texas, whose potential projects happened to be 

concentrated in the eastern part of the state. 

Considering only small hydro and low power, 

conventional turbine project sites, the map shows 

that sites abound East of the Mississippi River 

particularly in the Appalachian Mountains, on 

tributaries of the Mississippi River, in the Rocky 

Mountains, in the Sierra Mountains, and in the 

Coastal Ranges in California, Oregon, and 

Washington. 

Summaries addressing the water energy 

resources and feasible potential projects in each 

state are provided in Appendix B. These 

summaries include tabular data and graphical 

presentations of the gross power potential of state 

water energy resources by power category and the 

hydropower potential of potential projects by 

power class. Distributions of the number and 

group hydropower of low power and small hydro 

potential projects are presented in ranges of 

hydropower potential. These distributions show 

relative numbers of projects of various sizes and 

their contribution to the total, power class, 

hydropower potential. Each summary concludes 

with a state map showing the locations of low 

power and small hydro potential projects. 

4.4 Potential Project Location 

and Attributes Provided by 

the Virtual Hydropower 

Prospector 

In order to go beyond the summary data 

presented in this report and present information 

about individual water energy resource sites and 

potential projects, the data used and produced in 

this study were incorporated into a GIS application 

and made publicly available on the Internet. This 

application is called the VHP, and it is accessible 

at http://hydropower.inl.gov/prospector/. The VHP 

desktop displaying a map of the Pacific Northwest 

Region is shown in Figure 21. Its purpose is not 

only to display water energy resource sites and 

potential projects on regional maps and provide 

extensive attribute information about them, but 

also to show sufficient context features so that the 

application user can perform preliminary, 

customized feasibility assessments. For this 

purpose, the user can elect to display the following 

context features: 

•	 Hydrography 

•	 Power system (hydroelectric plants, other 

power plants, transmission lines, and 

substations) 

•	 Transportation (roads and railroads) 

•	 Areas and places (city centers; populated 

areas; county, state, and hydrologic region 

boundaries) 

•	 Land Use (exclusion zones based on federal 

and statutes and policies and environmental 

sensitivities; and land that is the purview of 

federal agencies including: Bureau of Indian 

Affairs, Bureau of Land Management, Bureau 

of Reclamation, Department of Defense, U.S. 

Forest Service, U.S. Fish & Wildlife Service, 

U.S. Park Service). 

In addition to displaying these features on the 

map, attribute information about them is also 

provided by the application. 

33 
34 

Legend 

Thumbnail 

Map 

Information 

Window 

Figure 21. Desktop of the Virtual Hydropower Prospect GIS application showing its areas for display and control. 
5. CONCLUSIONS 

This study has refined the results of the 

previous assessment of the water energy resources 

of the United States (Hall et al. 2004) by 

accounting for environmentally sensitive areas as 

zones in which hydropower development is 

unlikely. It has extended the previous study by 

identifying water energy resource sites that are 

feasible to develop and estimated their 

hydropower potential based on a realistic 

development model and associated development 

constraints. Of the approximately 300,000 MWa 

of total, gross power potential of U.S. natural 

stream water energy resources, only about 10% 

has been developed. About 30% are located in 

zones where development is unlikely. The 

remaining 60% of over 170,000 MWa have not 

been developed and are not restricted from 

development based on information sources used in 

the assessment. Of this potential, it was found that 

nearly 100,000 MWa of gross power potential 

could feasibly be developed. This feasible 

potential corresponds to nearly 130,000 potential 

low power and small hydro projects. Estimation of 

the hydropower potential of these sites indicates 

30,000 MWa of new power supply could feasibly 

be developed in the United States. 

There are a large number of feasible potential 

projects to choose from, and they are located such 

that most states could benefit from a significant 

amount of additional renewable energy if they 

were developed. Development of the 5,400 

feasible small hydro projects alone would provide 

more than a 50% increase in U.S. hydroelectric 

generation. Six western states, California, 

Washington, Alaska, Idaho, Oregon, and Montana, 

have potential project sites representing 

particularly high amounts of hydropower potential. 

With the exception of Washington, which already 

has the highest amount of hydroelectric generation 

among the states by a wide margin, these states 

have sufficient hydropower potential to increase 

their generation by between 60 and 1600%. Alaska 

has sufficient hydropower potential to increase its 

hydroelectric generation by nearly a factor of 16. 

Hawaii is also noteworthy, because it has the 

highest density of potential projects, which if 

developed, would also increase its hydroelectric 

generation by more than a factor of ten. Beneficial 

increases are not limited to just the western states. 

This study has shown that 41 states distributed 

around the country have sufficient potential to 

increase their generation by at least 50%. These 

facts illustrate that beneficial renewable water 

energy resources are under utilized throughout 

most of the country. 

The development model used to assess 

hydropower potential is a configuration not 

requiring a total obstruction of the water course or 

the creation of a reservoir. Eighty-four percent of 

the identified hydropower potential could be 

developed using existing technology. Of the 

current U.S. hydroelectric plant population, 92% 

are small hydro or low power plants based on their 

annual average power. These facts illustrate that 

while research and development may lead to new 

configurations, use of new materials, and 

increased efficiencies, significant gains in 

generation can be achieved without large research 

and development investments or the need to 

demonstrate that low power and small hydro 

plants are technologically feasible. 

Water energy resource sites were designated 

as being feasible for development in this study 

based on a set of feasibility criteria. Local land 

use, policies, and environmental sensitivities not 

accounted for in the study may render some of the 

identified potential projects unfeasible. Economic 

factors may also affect the development viability 

of some sites. The study also did not include a 

comprehensive assessment of the economic 

viability of the identified potential projects. An 

elementary consideration was given to acceptable 

costs of site accessibility and power transmission. 

However, the costs of licensing, construction, 

mitigation, operation and maintenance, availability 

of financing, and the potential income from 

purchased power were not evaluated. Current 

trends may make projects that are not 

economically viable now become viable in the 

future. These trends include: the rising cost of 

fossils fuels, the establishment of state renewable 

portfolio standards, carbon credits, transmission 

grid load and energy security considerations 

favoring distributed generation, and federal 

incentives to promote sustainable energy 

production and U.S. energy independence. 

35 
 

The hydropower potential of feasible potential 

projects was based on a development model and 

restrictions on working flow rate and hydraulic 

head. Equipment efficiency and penstock pressure 

losses were not included, which would reduce 

estimated hydropower potentials. While annual 

mean flow rates were used to estimate power 

potential, water availability based on flow duration 

was not. Some sites could be rendered unfeasible 

when equipment related power losses and water 

availability are included in the feasibility 

assessment. Counterbalancing these power 

potential reducing factors are the facts that more 

than half the stream flow may be available for 

power generation at some sites, thus increasing 

both power potential and availability. Dams may 

exist at some sites, increasing the power potential 

because of the existence of more hydraulic head 

than was estimated and increasing the likelihood 

of development due to previously mitigated 

environmental concerns and significantly reduced 

development costs. 

This study and the companion development of 

a publicly available GIS application on the 

Internet has shown that the value of research can 

be enhanced and extended by providing access to 

detailed information and tools for individuals to 

further research the subject matter from their 

perspective. The ultimate value of the study is the 

conclusion that sufficient, untapped power 

potential from water energy resources exists in 

most places in the United States to warrant further 

evaluation as sources of sustainable energy 

production and has shown the most likely 

locations meriting further evaluation. The Virtual 

Hydropower Prospector GIS application on the 

Internet provides a tool for customized preliminary 

site evaluations. However, site specific evaluations 

of development feasibility and power potential 

considering engineering and economic aspects of 

the potential project are essential. 

36 
6. RECOMMENDATIONS 

The feasibility assessment that has been 

performed could be further refined to address 

additional factors including: 

•	 Equipment efficiencies and energy losses 

•	 Resource duration and availability 

•	 Local land use and environmental sensitivities 

•	 Economic feasibility considering development 

costs and incentives, power marketing, and 

available financing. 

Incorporation of these additional factors for all the 

potential projects identified by the screening 

performed in the present study would require 

significant funding. As with any federally funded 

research and development, there is the question of 

at what point research that could not be funded by 

industry has been completed and sufficient 

information has been provided to enable industry 

to explore and develop specific opportunities. The 

need for federally funded refinement of the 

feasibility assessment is not clear. Such 

refinements are possible, but are probably 

dependent on an expression of industry need. 

The usefulness of VHP GIS application could 

be enhanced by several upgrades. At present, the 

application displays color-coded, shaded relief 

only when a large area is displayed. The relief is 

turned off when the user zooms into a local area 

because the relief is based on 1 km DEMs, 

resulting in distracting pixilation beyond a certain 

level of zoom. The relief display could be 

upgraded using GIS data layers based on at most 

90 m DEMS, allowing the user to view the 

topography of local areas and be better able to 

evaluate topographic implications affecting 

development. Additional feature sets and 

references that could be added include: 

•	 Locations and attributes of all existing U.S. 

dams from the National Inventory of Dams 

•	 Reference added to site and potential project 

attributes to access the Bureau of Land 

Management’s hydropower site surveys 

•	 Locations and attributes of protected areas as 

defined by the Northwest Power and 

Conservation Council. 

Canvassing hydropower stakeholders would no 

doubt lead to the identification of other feature sets 

that should be made available for display and 

reference. 

Entities controlling large land holdings, such 

as the U.S. military and Indian tribes, would 

benefit from customized versions of the 

assessment studies that have been performed. Such 

assessments would present subsets of the 

countrywide information to identify water energy 

resources and potential projects on the land under 

their purview. This would assist them in planning 

and securing funding, and if implemented, would 

provide energy security while providing electricity 

for their residents and operations. 

The tools and techniques that have been 

developed for assessing the United States natural 

stream resources could be applied anywhere in the 

world. Other developed countries and particularly 

developing countries would benefit from an 

assessment of their resources, the identification of 

promising development sites, and a GIS tool to 

assist in site evaluation and planning development 

of water energy resources. 

The resource assessment and subsequent 

feasibility assessment that have been performed 

were limited to natural stream, potential energy, 

water energy resources. The United States has 

other abundant sources of water energy that could 

be harnessed including: 

•	 Locations on natural streams with little or no 

elevation difference, but sufficient velocity 

and depth to accommodate hydrokinetic 

turbines 

•	 Constructed waterways 

•	 Tidal estuaries 

•	 Ocean currents 

•	 Ocean waves. 

Efficient development of these resources would be 

aided by determining the spatial distribution of 

their gross power potential, identifying feasible 

development sites, and estimating the realistic 

power potential at these sites. All stakeholders and 

particularly developers would greatly benefit from 

a GIS application addressing these resources like 

37 
the VHP. Such a tool would not only provide 

information about resources, but would help to 

ensure that investment is not made in areas where 

development is unlikely to succeed. 

Small hydropower developers would benefit 

from two information resources: a catalog of small 

hydropower technologies and a cost estimating 

guide that would assist them in making 

preliminary estimates of development costs. A 

pilot technology catalog (Hall & Dalton 2004) was 

published, but was not fully developed. A catalog 

of this type would serve the obvious function of 

informing developers of equipment available for 

their project. Because it was envisioned that the 

catalog would also contain technologies that have 

not reached the commercial stage of development, 

it would have the benefits of exposing promising 

technologies to additional development and 

revealing gaps where new technologies are 

needed. In addition to knowing what technologies 

are available, developers need to be able to get 

preliminary estimates of development costs 

including: licensing, construction, mitigation, and 

operations and maintenance. A previous study 

(Hall et al. 2004) provided cost estimating tools 

for these costs, but was limited to projects having 

nameplate capacities of 1 MW or greater. A 

reference that focused on low power and small 

hydro projects would provide greater applicability 

to these power classes of hydropower projects. 

38 
 

7. REFERENCES 

Connor, A. M., J. E. Frankfort, and B. N. Rinehart, 

1998, U.S. Hydropower Resource Assessment 

Final Report, DOE/ID-10430.2, 

December 1998.e 

ENERmap, 2005, U.S. power system GIS data 

layer purchased from ENERmap, LLC 

January 2005. 

ESRI, 2004, Environmental Systems Research 

Institute (ESRI) StreetMap data layer, 2004. 

Federal Energy Regulatory Commission, 1998, 

Hydroelectric Power Resources Assessment 

(HPRA) Database. 

Hall, D. G., R. T. Hunt, K. S. Reeves, and 

G. R. Carroll, 2003, Estimation of Economic 

Parameters of U.S. Hydropower Resources, 

INEEL/EXT-03-00662, June 2003.e 

Hall, D. G., S. J. Cherry, K. S. Reeves, R. D. Lee, 

G. R. Carroll, G. L. Sommers, and 

K. L. Verdin 2004, Water Energy Resources 

of the United States with Emphasis on Low 

Head/Low Power Resources, DOE/ID-11111, 

April 2004. 

Hall, D. G. and J. L. Dalton, 2004, Catalog of Low 

Power Hydropower Technologies, 

DOE/NE-11181, October 2004. 

Verdin, K., and S. Jenson, 1996, “Development of 

Continental Scale DEMs and Extraction of 

Hydrographic Features,” Proceedings of the 

Third International Conference/Workshop on 

Integrating GIS and Environmental Modeling, 

Santa Fe, New Mexico, January 21–26, 1996. 

(CD-ROM available from National Center for 

Geographic Information and Analysis, Santa 

Barbara, California, 93106, USA). 

Vogel, R. M., I. Wilson, and C. Daly, 1999, 

“Regional Regression Models of Annual 

Streamflow for the United States,” Journal of 

Irrigation and Drainage Engineering, 

May/June 1999, pp. 148–157. 

e. This report is accessible in pdf format on the Internet at: 

http://hydropower.inl.gov/resourceassessment/ 

39 
40 
Appendix A 

Description of Exclusion Zones 

A-1 
A-2 
Appendix A 

Description of Exclusion Zones 

In this study, exclusion zones were areas in 

which development of new hydroelectric plants is 

highly unlikely either because of land use 

designated by federal statutes and policies or 

because of known environmental sensitivities. 

These zones were used to apply the feasibility 

criteria stipulating that a water energy resource 

site must not be located in an exclusion zone if it 

is to be designated as a feasible potential project. 

Geographic information system (GIS) tools were 

used to determine whether any part of a stream 

reach corresponding to a water energy resource 

site intersected the polygon area representing the 

exclusion zone. If any part of the reach intersected 

the zone, the site was designated as unfeasible for 

development. However, if no part of the reach 

intersected the zone, no matter how close to the 

zone boundary it is, the exclusion zone feasibility 

criteria were considered to be met affirmatively. 

The two sections of this appendix each describe 

one of the two types of exclusion zones used in the 

study and the data that was used for analysis. 

States, regional jurisdictions, and local 

jurisdictions have also designated protected areas 

that are most likely excluded from hydropower 

development. However, information regarding 

these protected areas is scattered among numerous 

state, regional, and local government agencies. 

Much of this information is not yet in digital 

format, and much of the digital data are not 

available online. 

Determining the boundaries of lands protected 

by nonfederal agencies would have entailed 

contacting a large number of agencies in the 

country and collecting and digitizing multiple 

paper datasets in a variety of formats. Such an 

effort was beyond the scope of the study. It is 

fortunate that the Conservation Biology Institute 

provides georeferenced data for environmentally 

sensitive areas as is discussed in Section A-2. 

A-1. Federal Exclusion Zones 

Two GIS data layers from the National Atlas 

of the United States were used to locate federal 

exclusion zones. The first layer, “Federal and 

Indian Lands,” contains the boundaries of all 

federal lands in the United States, subdivided into 

categories such as national parks, national 

monuments, Indian reservations, military bases, 

and DOE sites. The second layer, “Parkways and 

Scenic Rivers,” contains federally protected linear 

features such as National Wild and Scenic Rivers 

and National Parkways. Both GIS data layers are 

available online from the National Atlas of the 

United States website at 

http://www.nationalatlas.gov/atlasftp.html. 

The categories of federal lands listed in the 

GIS dataset “Federal and Indian Lands” were 

reviewed to determine categories corresponding to 

areas in which hydropower development is highly 

likely to be excluded. Based on this review, the 

following categories of federal lands were selected 

as exclusion zones: 

• National battlefields 

• National historic parks 

• National parks 

• National parkways 

• National monuments 

• National preserves 

• National wildlife refuges 

• Wildlife management areas 

• National wilderness areas. 

All the federal lands in these categories were 

used to create an “excluded federal lands” GIS 

data layer. Similarly, all national wild and scenic 

rivers were extracted from the National Wild and 

Scenic Rivers and National Parkways data 

A-3 
 

layer to create a GIS data layer composed 

exclusively of Wild and Scenic Rivers. Because 

the “wild and scenic rivers data layer” contained 

only the rivers themselves, but no adjoining land, 

all land within one kilometer of a wild and scenic 

river reach was designated as an excluded area. 

These areas were combined with excluded federal 

lands to create a final “federal exclusion zone” 

GIS data layer that contains the boundaries of all 

lands and shorelines excluded from hydropower 

development. 

A-2. Environmentally Sensitive 

Exclusion Zones 

The Conservation Biology Institute 

(http://www.consbio.org/) provides a GIS data 

layer containing environmentally sensitive areas 

designated by four gap analysis program (GAP) 

categories with GAP-1 being the most restrictive 

and GAP-4 being the least restrictive. The 

definitions of the GAP categories are given in 

Table A-1. 

For the purposes of this study, areas 

designated with GAP codes 1 and 2 were 

considered to be exclusion zones in which new 

hydropower development is highly unlikely. The 

types of land use areas designated as GAP-1 and 

GAP-2 are enumerated in Tables A-2 and A-3, 

respectively. Many of the same types of land use 

areas appear in both lists, but were apparently 

discriminated based on the specific use restrictions 

for each individual area. Many of the exclusion 

zones based on GAP-1 and GAP-2 areas from the 

Conservation Biology Institute are coincident with 

areas that were considered federally designated 

exclusion zones. No individual area use 

restrictions were considered for federal exclusion 

zones. 

A-4
 
Table A-1. GAP codes used by the Conservation Biology Institute to designate land use restrictions based 

on environmental sensitivities. 

GAP Code Description 

GAP Code 1 

An area having permanent protection from conversion of natural land cover and a 

mandated management plan in operation to maintain a natural state within which 

disturbance events (of natural type, frequency, intensity, and legacy) are allowed to 

proceed without interference or are mimicked through management. Gap Code 1 

examples include national parks, wilderness areas, and nature preserves. 

GAP Code 2 

An area having permanent protection from conversion of natural land cover and a 

mandated management plan in operation to maintain a primarily natural state, but 

which may receive uses or management practices that degrade the quality of existing 

natural communities, including suppression of natural disturbance. Gap Code 2 

examples include state and provincial parks, wildlife refuges, and national recreation 

areas. 

GAP Code 3 

An area having permanent protection from conversion of natural land cover for the 

majority of the area, but subject to extractive uses of either a broad, low-intensity type 

(e.g., logging) or localized intense type(e.g., mining). It also confers protection to 

federally listed endangered and threatened species throughout the area. Gap Code 3 

examples include national forests, wildlife management areas, and Bureau of Land 

Management lands. 

GAP Code 4 

There are no known public or private institutional mandates or legally recognized 

easements or deed restrictions held by the managing entity to prevent conversion of 

natural habitat types to anthropogenic habitat types. The area generally allows 

conversion to unnatural land cover throughout. 

A-5
 
 

Table A-2. Types of land use areas designated as GAP Code 1 by the Conservation Biology Institute. 

Adaptive Management Area National Recreation Area Research Natural Area 

Administratively Withdrawn National Reserve Scenic Recreation Area 

Area of Critical Environmental 

Concern National Scenic-Research Area Scenic Research Area 

Botanical Reserve (SIA) National Volcanic Monument Special Designation 

Congressionally Withdrawn National Wildlife Refuge Special Interest Area 

Conservation Land Natural Area State Park 

Ecological Reserve Nature Conservancy Preserve State Proposed Research Natural Area 

Geologic Area Nature Preserve State Scenic Waterway 

Late Successional Reserve Open Water State Wildlife Reserve 

Management Plan Area OSPRSSW/Deschutes Tribal Primitive Area 

National Forest Other BLM Land Tribal Wilderness 

National Grassland Other COE Land Water 

National Historic Park Other National Park Land Wild and Scenic Area 

National Historical Park Private Conservation Land Wild and Scenic River 

National Memorial Parkway Private Institution Managed for 

Biodiversity Wilderness 

National Monument Private Land Wilderness Area 

National Outstanding Natural 

Area Private Lands Wilderness Study Area 

National Park Proposed Research Natural Area Wildlife Habitat Management Area 

Table A-3. Types of land use areas designated as GAP Code 2 by the Conservation Biology Institute. 

Area of Critical Environmental Concern Natl River & Wild & Scenic Riverway Research Natural Area 

BLM Holding Natural Area Special Designation 

BLM/National Wildlife Refuge PW Natural scenic area Special Interest Area 

BLM/Protective Withdrawal (PW) Open Water State Lands 

Botanical Area Other BLM Land State Lease 

Botanical Emphasis Area Other COE Land State Memorial 

Conservation Easement Other Federal Land State Natural Area 

Corporate easement Other Federal Lands State Park 

Ducks Unlimited Managed Other ODFW Land State Recreation Area 

Fish & Game Access Area Other USFWS State RNA 

Fish & Game Management Area Other USFWS Land State Scenic Waterway 

Game Management Area Park Land State Wildlife Recreation Area 

Game Range Preservation Easement TNC Easement 

Instant Study Area Primitive Area Tribal Wilderness Buffer Zone 

Lease Primitive State Park USFS/Protective Withdrawal (PW) 

Local Land Trust Preserve/Easement Privately owned, DU managed CE Water 

Military Reservation Privately owned, Fvlt managed CE Wayside 

National Conservation Area Privately owned, MLR managed Wild and Scenic Area 

National Forest Privately owned, MLR managed CE Wild and Scenic River 

National Grassland Privately owned, MLR managed, PW Wild River/Wilderness Area 

National Monument Privately owned, TNC managed Wilderness Area 

National Park Privately owned, TNC managed CE Wilderness Study Area 

National Recreation Area Privately owned, TNC managed other Wildlife Area 

National Scenic Area Privately owned, TNC managed regis Wildlife Habitat Management Area 

National Wild & Scenic River Proposed Natural Area Wildlife Management Area 

National Wildlife Refuge Proposed Research Natural Area 

Native American Lands Proposed RNA 

A-6