Presented by: Civil Engineering Academy Detention/Retention Ponds - PowerPoint PPT Presentation

Presented by: Civil Engineering Academy

Detention/Retention Ponds Presented by: Civil Engineering Academy

 Also known as impounding reservoir or retention watershed (CERM Ch. 20).

 Analysis to determine the proper size of a reservoir or dam, or to evaluate the ability of an existing reservoir to meet water demands. Reservoir sizing Methods (CERM Ch. 20) 1. Non sequential drought method 2. Modified Rational Method 3. Reservoir routing method 4. Stochastic simulation method

 Formula: V n+1 = V n + (inflow) n – (discharge) n – (seepage) n – (evaporation) n Where: V = storage volume and subscripts n means present data n+1 means the next iteration of data

 Evaporation ◦ Can be estimated from analytical relationships or by evaluating data from evaporation pans.  Evaporation Pan Formula E R = ∑K P E P Eq. 20.48 Where: K P = pan coefficient, typically 0.7 – 0.8. E p = evaporation loss

 An evaporation pan with coefficient of 0.8 is used to estimate the evaporation loss of a reservoir. For one day, it shows an evaporation loss of 0.9. Determine the evaporation loss of the reservoir. Solution: E R = ∑K P E P E R = (0.8)(0.9 in) = 0.72 in K P = 0.8 E p = 0.9

 For reservoir sizing, use the mass diagram method.

Six Minute Solutions – Water Resources Prob. 52, Depth

Prob. 52, Depth (continued)

 Reservoir Sizing Problems!  Next topic: Pressure Conduit