PART 1 - INTRODUCTION TO SITES B. History and Focus of the SITES Software and its Application SPECIALTY WORKSHOP: SITES TRAINING AND INTRODUCTION TO WINDAM ASDSO Dam Safety 2008

SEMINAR OBJECTIVES History of NRCS dam design Evolution of the software tools used by USDA What is unique about SITES

Farm Pond Design From the late 1930s the experience the agency gained from the design of farm ponds was transferred to the design of small watershed structures in the late 1940s.

USDA Small Watershed Program Public Law – Flood Control Act of Appropriation Act that authorized 62 pilot watershed projects in 36 states Public Law – Watershed Protection and Flood Prevention Act of 1954.

Watershed Project Locations

Watershed Dams

PERM, POOL TAIL- WATER TOP DAM CREST AUX. PERM. POOL FBH SDH PSH CONDUIT CREST PS DESIGN FLOW (SDH) TAIL- WATER AUX. SPLWY. EXIT CHANNEL INLET CHANNEL TOP DAM INLET CHANNEL EXIT CHANNEL TAILWATER ELEV CREST AUX..

Criteria for Design Each of the 6 regions in SCS used their own criteria for design until about 1957 when Eng. Memo 3 was issued. Eng. Memo. 27 (Rev) for design of small dams was issued in TR60 replaced Eng. Memo. 27 in –(Rev. 1985, Amended 1990, Rev. 2005)

TR-60 Overview General (Dam Classification, breach discharge, utility cables, pipelines, etc.) Hydrology Sedimentation Geologic Investigations Earth Embankment and foundations Principle spillways Auxiliary Spillways

TR-60 Overview General (Dam Classification, breach discharge, utility cables, pipelines, etc.) Hydrology Sedimentation Geologic Investigations Earth Embankment and foundations Principle spillways Auxiliary Spillways

Hazard Classification and Risk From the late 1950s the criteria allowed greater risk with low hazard structures than it did with high hazard structures. CLASSES OF DAMS Low Hazard Class Significant Hazard Class High Hazard Class

Hand Flood Routing

Hydrology Spillway discharge and floodwater storage criteria Design Hydrographs –Principle Spillway Hydrograph –Stability Design Hydrograph –Freeboard Hydrograph Dams in Series

Auxiliary Spillways Convey excess water through, over, or around a dam. Usually open channels excavated in natural earth, earthfill, and/or rock. Must pass the SDH at safe velocities and meet allowable effective stress. Must pass the FBH at water levels < the top of dam and not breach.

Mainframe Computer Routing Mainframe Computer Programs were developed in the 1960s to replace hand routing methods. PSIN for Principal Spillway INput and REServoir INput routine RSIN were used through the 70s Dams and Dams2 were used concurrently with PSIN and RSIN.

Design & Analysis of Earth Spillways Team SITES TIME LINE DAMS DAMS2 Interim Version DAMS2 & Manual Emergency Spillway Flow Study Task Group DAMS2 PC Test Version 21 new Control Words added to Dams SITES (Windows Version with IDE) SITES 2000 – Sites in Series SITES October 2007

PC VERSIONS In 1989 the first DOS PC version of Dams2 was released as a test version. SITES – Stability & Integrity Technology for Earth Spillways. (Name change 1994) In 1998 the first windows version of SITES was released.

Bulk Length = Bu & Resistance > Attack? TR – 52 A Guide for Design and Layout of Earth Emergency Spillways (1973) Sd Inlet ChannelExit Channel 1 1 Su 2 ft. 2/SuL2/Sd Longitudinal Bulk Length = Bu Bu = L + 2/Su + 2/Sd L = Length of level section of spillway in ft. Su = slope of upstream part in ft./ft. Sd = slope of downstream part in ft./ft. Control Section

1983 -The ESFSTG was formed ARS & SCS established DAES Team

Earth Spillway Flow Study Task Group (ESFSTG) Established in January 1983 Assignment - Visit dams with major spillway flows or damage - Gather spillway performance data\ - Analyze data - Prepare performance reports Group - Civil Engr., Geologist, Hyd. Engr.

Performance of ESFSTG From 1983 to 1991, SCS had spillway flow at over 1450 sites. ESFSTG and ARS visited approximately 125 sites. 10 spillway performance reports were published.

Range of Sites Dam height Spillway width Exit channel slope Exit condition Spillway materials Maintenance feet feet % Good to vert. Drop Rock to sand Excellent to very poor

Range in Flow Parameters Reservoir head above crest Maximum velocity Flow duration Total discharge / bottom width (oe/b) feet ft. / Sec hours 1 to 91 AF / ft.

Observed Conditions at the Sites Most spillways functioned as intended A few spillway crests breached (4 sites, 1 drained pool) Some dams overtopped (8 sites, 0.3 to 1.5 ft.)

LABORATORY SPILLWAY MODEL Flow concentration Failure vegetal covers Surface detachment processes Headcut migration.

Design and Analysis of Earth Spillway Team (DAES) Joint ARS/SCS team Established in July 1991 Purpose - To develop a model to predict breach potential for earth spillways Team members - ARS: Temple and Hanson - NRCS: Moore and Brevard

DAES Study Purpose Study spillway performance Evaluate spillway design criteria Revise criteria where necessary Incorporated spillway erosion model into DAMS-2 resulting in SITES

SITES ? ? ? Watershed Rainfall-Runoff Streamflow routing Reservoir Routing Principal spillway rating Auxiliary spillway rating NRCS dam design features Earth Spillway Analysis

SITES Able to route 3 Hydrographs at a time. Principal spillway – PS Auxiliary spillway – SDH Freeboard -- FBH

SITES The program will provide the user with a principal spillway rating for a set of standard NRCS risers. The rating assumes a free outlet for the principal spillway conduit. A standard riser has the dimensions of Dx3D.

SITES The program has the ability to rate a vegetated earth spillway in either critical or subcrital flow. Mixed flow is also allowed between vegetated and nonvegetated reaches in the spillway.

Auxiliary Spillway Profile Inlet Natural Ground Constructed Inlet Channel Constructed Exit Channel Exit Natural Ground Tie Sta.

SPILLWAY SURFACE STATION ELEVATION, ft

STABILITY The tractive stress of the vegetated earth spillway is computed from the 6 hour SDH storm.

INTEGRITY This is the design to make sure the spillway does not breach from the FBH storm. This requires geologic information from the entrance of the spillway through the valley floor. Valley floor is the lowest point where erosion begins.

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