Volume 2-05, Chapter 3 - City of Wichita

Section 3.2.1 - Stomwater Pond
Step 7
Step 8
Step 9
Determine elevation and orifice size for channel protection extended detention:
Wet Pond: The CP V orifice is placed at the top of the permanent WQ V pool. The
preferred method is to route the 1-year, 24-hour inflow hydrograph through the pond,
and select an orifice size that provides 24 hours of detention between the centroid of
the inflow hydrograph and the centroid of the outflow hydrograph.
In lieu of the routing method, a “simplified method” is available for determining the
CP V and for configuring the CP V orifice. This method is described in detail in
Chapter 4. In summary, the method consists of estimating the peak inflow and
outflow to and from the pond for a 24-hour detention time, the CP V , and the
corresponding maximum head on the orifice. This information is then used to size
the orifice.
Wet Extended Detention Pond and Wet Extended Detention Micropool Pond: For wet
extended detention ponds, the CP V orifice is typically located at the top of the
permanent part of the WQ V pool. As with the wet pond, the preferred method is to
route the 1-year, 24-hour inflow hydrograph through the pond, and select the orifice
size that provides 24 hours of detention between the centroids of the inflow and
outflow hydrographs. However, in some cases, the simplified method discussed
above may be used. The simplified method is strictly applicable to the situation
where the active pool (in this case the CP V pool and the extended detention portion
of the WQ V pool) is controlled by one or more orifices at the same elevation.
However, it is rare that the WQ V orifice alone can serve to regulate both the WQ V
and CP V . In most cases, a CP V orifice is also required. If the elevations of the
centers of the WQ V and CP V orifices are “approximately” the same, then the
simplified method is applicable. Until further information is available, the elevations
of the centers of the orifices will be considered “approximately” the same if the
difference between the center elevations does not exceed 20% of the CP V depth.
Prepare hydrology analysis for floods and design embankment(s) and spillway(s):
Size additional control structure orifices, weirs and emergency spillway as required
for flood control and freeboard.
Provide safe passage for the 100-year event.
Investigate potential pond hazard classification:
The design and construction of stormwater management ponds are required to follow
the latest version of the Kansas dam safety guidelines, where applicable.
Step 10 Design inlets, sediment pre-treatment facilities, outlet structures, maintenance
access, and safety features:
See Volume 2, Chapter 5 for more details.
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Volume 2, Technical Guidance