1. Logan Dry Canyon Detention Basin Design Case Study
How to determine the size of the detention basin to protect the community?
Design infrastructure to accommodate the release of floodwater and convey it safely to Logan River

2. Elements of the Design Solution
Determine watershed and soil properties
Determine design precipitation event
Determine design hydrograph
Size the detention basin and outlet works trading off the capacity required for stormwater conveyance versus capacity required for detention pond

3. Length from furthest point

4. Soil Texture Triangle
From Mays, 2011, Ground and Surface Water Hydrology

5. Runoff curve numbers for arid and semiarid rangelands.
ftp://ftp.wcc.nrcs.usda.gov/wntsc/H&H/NEHhydrology/ch9.pdf

6. Table Green – Ampt infiltration parameters for various soil classes (Rawls et al., 1983). The numbers in parentheses are one standard deviation around the parameter value given.
Soil Texture
Porosity n
Effective porosity e
Wetting front soil suction head  (cm)
Hydraulic conductivity K (cm/hr)
Sand
0.437
( )
0.417
( )
4.95
( )
11.78
Loamy sand
( )
0.401
( )
6.13
( )
2.99
Sandy loam
0.453
( )
0.412
( )
11.01
( )
1.09
Loam
0.463
( )
0.434
( )
8.89
( )
0.34
Silt loam
0.501
( )
0.486
( )
16.68
( )
0.65
Sandy clay loam
0.398
( )
0.330
( )
21.85
( )
0.15
Clay loam
0.464
( )
0.309
( )
20.88
( )
0.1
Silty clay loam
0.471
( )
0.432
( )
27.30
( )
Sandy clay
0.430
( )
0.321
( )
23.90
( )
0.06
Silty clay
0.479
( )
0.423
( )
29.22
( )
0.05
Clay
0.475
( )
0.385
( )
31.63
( )
0.03

9. Detention basin geometry
The sides A, B, C, and D are sloped 1:2, 1:2, 1:5, and 1:1, respectively