Volume 2-05, Chapter 3 - City of Wichita
Volume 2-05, Chapter 3 - City of Wichita
Volume 2-05, Chapter 3 - City of Wichita
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Section 3.2.1 - Stormwater Pond<br />
1' MIN. FREEBOARD<br />
100 - YEAR<br />
ELEVATION<br />
PERMANENT POOL<br />
ELEVATION<br />
12" - 18"<br />
10' - 15'<br />
AQUATIC BENCH<br />
10'<br />
SAFETY BENCH<br />
IF NEEDED<br />
5:1 MAX, OR<br />
10:1 MAX 10:1 MAX<br />
3:1 MAX<br />
EXISTING<br />
GRADE<br />
BASIN<br />
FLOOR<br />
2:1 MAX<br />
EMERGENT WETLAND VEGETATION<br />
Figure 3-12 Typical Stormwater Pond Geometry Criteria<br />
D. PRETREATMENT / INLETS<br />
• Each pond shall have a sediment forebay or equivalent upstream pre-treatment at each<br />
inlet. A sediment forebay is designed to remove incoming larger sediment from the<br />
stormwater flow prior to dispersal in the larger permanent pool. Pretreatment consists <strong>of</strong> a<br />
separate cell, formed by an acceptable barrier between the forebay and pond. A forebay<br />
is to be provided at each inlet, unless the inlet provides less than 10% <strong>of</strong> the total design<br />
storm inflow to the pond. In some design configurations, the pretreatment volume may be<br />
located within the permanent pool.<br />
• A forebay must be sized to contain 0.1 acre-inch per impervious acre <strong>of</strong> contributing<br />
drainage and should be 4 to 6 feet deep. The pretreatment storage volume is part <strong>of</strong> the<br />
total WQ v requirement and may be subtracted from WQ v for permanent pool sizing.<br />
• A fixed vertical sediment depth marker shall be installed in the forebay to measure<br />
sediment deposition over time. The bottom <strong>of</strong> the forebay may be hardened (e.g., using<br />
concrete, paver blocks, etc.) to make sediment removal easier.<br />
• Pond inflow channels are to be stabilized with flared riprap aprons, or the equivalent. Inlet<br />
pipes to the pond can be partially submerged. Inflow pipe, channel velocities, and exit<br />
velocities from the forebay must be nonerosive.<br />
E. OUTLET STRUCTURES<br />
• Flow control from a stormwater pond is accomplished with the use <strong>of</strong> a principal spillway<br />
consisting <strong>of</strong> a concrete riser and barrel. The riser is a vertical pipe, typically with several<br />
weirs and/or orifices at various levels. The outlet barrel is a horizontal pipe attached to the<br />
riser that conveys flow under the embankment (see Figure 3-13). Where practicable, the<br />
riser should be located within the embankment for maintenance access, safety and<br />
aesthetics.<br />
<strong>Volume</strong> 2, Technical Guidance Page 3 - 33