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Project Summary

The Crow Creek Retention Basin project is designed to prevent future flooding in the region by temporarily storing the excess runoff in the basin then releasing the runoff into an appropriate facility. Hydrologic simulation of the watershed for a one hundred year return period created using HEC-HMS 4.1 estimated a maximum peak flow of 526 CFS and a volume of 76 AF. The basin design, modeled using VTPHUSM, was expected to attenuate up fifty percent of the peak flow before releasing the runoff into an existing culvert through a three-step rectangular weir structure. The basin was also designed to generate recreational value to the community by providing a sustainable habitat for fish and wildlife in the region. The basin design thus included a retention basin with a 15 ft. deep, 29 AF permanent pool, a 10 ft. deep, 50 AF control pool and an outlet structure. The engineering cost for the project was $47,234 and the construction cost was estimated to be approximately $834,480.

Construction Cost Estimate

The construction cost of the project involves preliminary site layout, demolition and earthwork. Dakota Tipis Habitat for Humanity will foresee the construction process. The Tribal Housing Authority at Crow Creek South Dakota will provide the funding for the project.   Before construction, the site need to be thoroughly survey. All underground utilities need to be marked. The location and dimension of the basin need to be layout. Trees and potential obstruction objects are to be removed from the basin area. Excavation is the main construction task in the project. The construction period should avoid rain reason in order to minimize any potential complication during construction. The construction of the riser box from the bottom of the basin require proper forming and concrete pouring. Rip rap should be placed at the top of the embankment in order to prevent erosion from overtopping. After construction, vegetation need to be rehabilitated in order to enhance the aesthetic value of the project. The construction cost was estimated to be $834,480.

Estimated Peak Flow and Hydrograph

peak flowhydrograph

Using the hydrologic model from HEC-HMS 4.1 and the Curve Number method, 15 minutes increment hydrographs and peak flow values were generated for the 2-year, 10-year and 100-year return period. The excess volume during a 100-year storm event constrained the overall volume of the basin. In addition, the peak flows from the three return periods also determined the design of the outlet structure. After multiple simulation runs from the program VTPHSUM, a three-steps concrete rectangular weir was selected for the design.


The rectangular weir model above showed the overall dimension of the structure. The weir consisted of three steps at different width and elevation which would allow the outlet structure to release water at different flow rate in accordance to the storm event. The ability to release an adequate amount of water would prevent the basin from overflow when its storage capacity exceeded.


Retention Basin Design


Figure 1: Basin Layout

The retention basin in this design consisted of two parts: the permanent pool and the control pool as showed in Figure 1. The permanent pool will serve as a sustainable habitat for the future fish and wild life population. The water in the permanent pool is expected to maintain a constant depth of at least 15 ft. year round. The depth of the permanent pool was designed so that the fish population can continue living in their habitat even when the basin’s surface gets frozen over the winter months. The control pool will serve as temporary water storage during a storm event thus preventing the runoff from flooding the area. The water in the control pool will be released through an outlet structure into an appropriate culvert. The volume of runoff associated with a 100-year storm will determine the overall dimension of the control pool.


Different Types of Water Basin-Consideration for Alternative Design

  • Detention Basin is a type of drainage basin that collects and temporarily stores the excess surface runoff then slowly release the runoff into a nearby stream.
  • Infiltration Basin is also a type of drainage basin but the runoff is discharge into an underground aquifer instead of a stream. The infiltration basin  is currently favored in the industry because of the simplicity of the design and high pollutant removal capability.
  • Retention Basin is a form of storage basin that permanently stores the surface runoff and partially release the runoff into a drainage system when necessary. Retention basin is usually design to alleviate flooding condition while adding aesthetic value to the surrounding area.

Burmister Classification of the Soil Samples

According to the Burmister classification system, soil is classified based on its grain size distribution for granular soil and plasticity index for cohesive soil. Figure-1 showed the results of the Atterberg limits test from the laboratory. The plasticity index of the soil was calculated using the liquid limit and plastic limit values.

Boring Location Elevation Liquid Limit % Plastic Limit % Plasticity Index
#1 0′-6′ 61.8 22.67 39
6′ – 8′ 81.7 29.81 52
#2 0′-6′ 54.8 23.14 32
6′-8′ 45.2 18.4 27

Based on the plasticity index from Figure-1, the cohesive soil was classified as Black Silty CLAY and the granular soil was classified as Yellow SAND trace Gravel.