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Earthen/Vegetated Auxiliary Spillway Erosion Prediction for Dams
    (Version 2005.1.11)                                  

NOTE: If Version 2005.1.5 is installed, it must be uninstalled. Version 2005.1.5 should not be used, due to errors in routing of long duration drawdowns.

SITES download button The Natural Resources Conservation Service, the Agricultural Research Service, and Kansas State University used government funds to develop the Water Resources Site Analysis Program (SITES) computer program. It may be downloaded for use and copying at no additional expense or license requirements.

     History                                  SITES User Guide             Erosion Technology

     Program Purpose                Design Guidance                Contact NRCS

     Features                                Example Data                    Downloads

     Integrated Development Environment (IDE)
               Training Materials          


Version Notes

2005.1.11 This version contains two bug fixes.  The rainfall data input of NRCS 24-hr Type 1A distribution was corrected. In addition, the watershed schematic now zooms in and out correctly.  One new added feature is the ability to import hydrographs in new file formats from WinTR-20.

2005.1.8: In previous versions, some elements in the watershed schematic screen were out of view and remained hidden.  In SITES version 2005.1.8 the user can view and select all watershed schematic elements for complex watersheds.  Computational results should be the same for versions 2005.1.6, 2005.1.7, and 2005.1.8.

2005.1.7: Fixed bug when user adjusted Windows 7 zoom setting other than 100%. Computational results should be the same for versions 2005.1.6 and  2005.1.7.

2005.1.6: Fixed error on starting water surface elevation in 2005.1.5.  Do not use version 2005.1.5.


The SITES software is a descendent of the DAMS2 program, a rainfall-runoff routing program developed for watershed dam design and analysis. SITES includes auxiliary spillway performance evaluation through the joint efforts of the Agricultural Research Service (ARS) and the NRCS. The Integrated Development Environment (IDE) for SITES was developed cooperatively by NRCS, ARS, and Kansas State University. The SITES computer program can be used for both TR-60 watershed dams and 378 CO-01 dams.

Program Purpose

SITES models watershed runoff  from a rainfall event and then routes the resulting hydrograph through a dam to hydraulically proportion the principal spillway and auxiliary spillway.  

SITES also models erosion in earthen and vegetated auxiliary spillways.  The three-phase  erosion model was jointly developed by the Agricultural Research Service (ARS) and the NRCS.

        1)   Phase one of the erosion or failure process is failure of the vegetal cover and
             the development of concentrated flow.
       2)   Phase two is downward erosion in the area of concentrated flow, resulting in
             headcut formation.
       3)   Phase three is downward and upstream movement of the headcut, potentially
             breaching the spillway.

Each phase is described by a set of threshold-rate relationships based on the process mechanics. A headcut erodibility index (Kh) describes the resistance of the exposed geologic materials to erosive attack during the third phase of the process. Aids for estimating this index are included in help screens and in supporting materials discussed below.


The Sites software has great flexibility in developing the auxiliary spillway rating and evaluating exit channel stability. SITES accepts vegetal retardance potential for flow resistance input as well as Manning's n, and flow resistance can vary from reach to reach in the spillway. SITES develops a spillway rating for subcritical exit channel flow. For both supercritical and subcritical flows, SITES evaluates exit channel stability using the allowable tractive stress approach.

When applied in design, the earth spillway erosion model incorporated into SITES is normally used to evaluate the potential for spillway breach under a freeboard hydrograph having at least 24 hours rainfall duration.

In addition to the auxiliary spillway erosion in SITES, WinDAM B also estimates erosion of an earthen embankment during overtopping.

SITES Integrated Development Environment (IDE)

  NRCS, ARS, and Kansas State University cooperatively developed the IDE included in the SITES software. The user can build complex watersheds using the watershed schematic screen. Watershed components include structures, sub-watersheds and channel reaches. In watershed models containing multiple dams, analysis focuses on the most downstream dam. Output includes a customizable summary table and graphical output showing hydrologic, structural, and hydraulic parameters.

SITES runs in Windows 98SE/2000/NT/XP/Vista/Windows 7/Windows 10 operating systems (version 2000 or later recommended). Minimum recommended RAM is 32 Mb. 

SITES User Guide

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The SITES User Guide (34.8 Mb) package contains SITES Water Resource Site Analysis Computer Program User’s Guide (210-9-8) documenting the capabilities and I/O requirements. Appendix A is a Quick Start guide for beginning users. The User's Guide describes use of the software through the integrated development environment as well as providing information to allow advanced users to access extended capabilities of the computational routine. 

Design Guidance

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The design guidance package (3.7 Mb) contains Chapters 50, 51, and 52 of NRCS NEH 628, TR-60, and NHCP-378. Chapters 50, 51, and 52 of NRCS NEH-628 contain auxiliary spillway layout and design guidance, details of the auxiliary spillway performance model, and procedures for estimating the headcut erodibility index, respectively. TR-60 and NHCP-378 describe NRCS design criteria and are essential references for development of input data for application of SITES. A spreadsheet is available to assist in calculating the Headcut Erodibility Index, khcalc.xls, (also in the design guidance package). Instructions for its use are contained within the spreadsheet itself and on pages 31-33 of NEH-628 Chapter 52 of the design guidance package. 

Example Data

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The example data package (15 Kb) includes example data for testing and becoming familiar with SITES. Data sets with the D2C extension may be imported into the IDE. The data sets were developed to illustrate program features only, and do not represent any real sites or conditions. 

Training Materials

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The training and tutorial package (20.9 Mb) contains Power Point® presentations and notes that may be used for training or as a self-study tutorial. These presentations were originally developed to train NRCS engineers and geologists in the use of the SITES software. A background in hydraulics and erosion mechanics is assumed. This package was developed for earlier versions of SITES and discussions may not reflect all capabilities of SITES 2005.

More Spillway Erosion Technology Information

The user is responsible to understand the complex spillway erosion processes, input variables required by the model, and the applicability of the model to design conditions. Publications documenting the underlying spillway erosion technology are available through the USDA ARS Hydraulic Engineering Research Unit in Stillwater, OK.

Contact NRCS

Karl Visser (ph: 817-509-3763 email:

Download List


SITES 2005 (version 2005.1.11) (8 Mb)

Sites 2005 Users Guide

Dam and Spillway Design Guidance Package (4 Mb)

Example Data (15 Kb)

Training/Tutorial Materials (21 Mb)

The use of trade names does not constitute endorsement by the developers or by the USDA.

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