Volume 2-05, Chapter 3 - City of Wichita

Section 3.2.1 - Stormwater Pond
3.2.1.6 Design Procedures for Stormwater Ponds
Step 1
Step 2
Step 3
Step 4
Compute runoff control volumes using the Integrated Design Approach: Calculate
the WQv, CPv or channel protection inflow hydrograph, and the peak flow control
inflow hydrographs using methods discussed in Volume 2, Chapter 4.
Confirm local design criteria and applicability:
Consider any special site-specific design conditions/criteria.
Check with local officials and other agencies to determine if there are any additional
restrictions and/or surface water or watershed requirements that may apply.
Determine pretreatment volume:
A sediment forebay is provided at each inlet, unless the inlet provides less than 10%
of the total design storm inflow to the pond. The forebay should be sized to contain
0.1 inches per impervious acre of contributing drainage and should be 4 to 6 feet
deep. The forebay storage volume counts toward the total WQ v requirement and
may be subtracted from the WQ v for subsequent calculations.
Determine permanent pool volume and water quality extended detention volume:
Wet Pond: Size permanent pool volume to 1.0 WQ v
Extended Detention Wet Pond: Size permanent pool volume to 0.5 WQ v . Size
extended detention volume to 0.5 WQ v .
Extended Detention Micropool Pond: Size permanent pool volume to 0.1 acre-inch
per impervious acre. Size extended detention volume to remainder of WQ v .
Step 5
Step 6
Layout pond grading and determine storage available for permanent pool and
extended detention water quality pool, as applicable:
This step involves designing the grading for the pond (establishing contours) and
determining the elevation-storage relationship for the pond. This typically requires a
trial and revision approach as the design is refined.
Include safety and aquatic benches.
Set WQ V permanent pool elevation based on calculated permanent pool volume and
the elevation-storage curve for the pond (see above).
Determine elevation and orifice size for extended detention portion of WQ V (for
extended wet detention ponds and micropool ponds):
Set orifice elevation at top of permanent pool.
Set top of extended detention pool based on extended detention volume and pond
elevation-storage curve.
By trial and revision, select an orifice size that will drain 90% of the WQ V in 24 hours.
The 90% criteria is intended to address the tendency of the drawdown method (see
Chapter 4 of Volume 2) to oversize the orifice.
Volume 2, Technical Guidance Page 3 - 39