Pactola Dam

Pactola Dam is situated at a point along Rapid Creek where the valley narrows and the creek has cut through a resistant, northwest trending ridge.  Rocks at the dam consist of a complex series of schists, slates and amphibolites lying in nearly vertical beds which strike in a northwest direction.  There is a small fold in the right abutment that modifies the strike of the beds and causes the axis of the dam to cross some beds twice.  The schistosity for the most part parallels the original bedding.  The amphibolite schist rocks are hard, jointed and usually weathered to shallow depths.  The slate beds contain abundant iron pyrite which weathers readily above the water table.

RegionFacilities in Great Plains | Great Plains Home Page
StateSouth Dakota
ProjectPSMBP-Rapid Valley Unit
Dam Type
WatercourseRapid Creek
Original Construction1952-1956
Modified Construction1987
National ID NumberSD01139
Hydrologic Unit Code

Structural Height245.00 ft
Hydraulic Height (Normal Operating Depth at Dam)199.50 ft
Top Parapet (Elevation)
Spillway Crest Elevation4621.50 ft
Crest Elevation4655.0 ft
Crest Length2236.00 ft
Crest Width
Base Width
Volume of Dam Construction Materials
Streambed at Dam Axis4422.00 ft
Top of Exclusive Flood Control Pool (Elevation)
Top of Joint Use Pool (Elevation)
Top of Active Conservation Pool (Elevation)4580.00 ft
Top of Inactive Conservation Pool (Elevation)4456.10 ft
Top of Dead Storage Pool (Elevation)4440.00 ft

Hydraulics & Hydrology
Total Water Storage at Elevation
Maximum Water Surface Elevation
Normal Water Surface Elevation4580.0 ft
Spillway Type
Auxiliary SpillwayNo
Spillway Capacity at Elevation245000.0 cfs at 4651.7 ft
Auxiliary Spillway Capacity at Elevation
Uncontrolled Spillway Capacity at Elevation
Outlet Works Capacity at Elevation1150.0 cfs at 4633.7 ft
Diversion Capacity at Elevation
Drainage Area
Hydrometeorological Report (HMR)
Probable Maximum Flood (PMF) Report

Contact Information
TitleArea Office Manager
OrganizationDakotas Area Office
AddressPO Box 1017
CityBismarck, ND 58501
Phone (Fax)701 250-4326
Phone (Office)701 250-4242
OrganizationCity of Rapid City
CityRapid, SD

Last updated: Apr 02, 2013