雨水调蓄池设计

Stormwater Management Pond Design Steps:

1.Feasibility study:

∙Hydrology - Dry pond or wet pond? If receive and retain enough flow from rain, runoff, and groundwater to ensure long-term viability.

∙Undrlying Soil - Underlying soils must be identified and tested. Soil permeability must be tested in the proposed Wet Pond location to ensure that excessive infiltration will not cause the WP to dry out.

∙According to the geological investigation and topographic features, select extended detention pond, wet retention pond, wetland pond.

2.Sizing Pond:

The area required for a Wet Pond (WP) is generally 1 to 3 percent of its drainage area. WPs should be sized to treat the water quality volume and, if necessary, to mitigate the peak rates for larger events.

∙Sediment Forebay - The forebay shall consist of a separate cell, formed by an acceptable barrier.

shall be sized to contain 0.1 inches per impervious acre of contributing drainage (The forebays should contain 10 to 15 percent of the total permanent pool volume and should be 4 to 6 feet deep). A fixed vertical sediment depth marker should be installed in the forebay to

measure sediment deposition over time.

∙Minimum Water Quality Volume (WQv)

∙Minimum Pond Geometry - Flowpaths from inflow points to outlets shall be maximized.

Flowpaths of 2:1 (length relative to width) whenever possible and irregular shapes are

recommended.

∙An average depth of 3 to 6 feet and a maximum depth of 8 feet, should shallow enough to minimize thermal stratification and short-circuiting and deep enough to prevent sediment

resuspension, reduce algal blooms and maintain aerobic conditions. Wet ponds should not be constructed within a natural watercourse.

∙Compute pre- and post- development peak flows for collected drainage area

∙Sizing the pond volumes to control 2-yr, 10-yr storms and safely pass 50-yr or 100-yr storm per local requirement.

∙Outlet devices are generally multistage structures with pipes, orifices, or weirs for flow control.

A reverse slope pipe terminating 2 to 3 feet below the normal water surface, minimizes the

discharge of warm surface water and is less susceptible to clogging by floating debris.

∙Outlet Structure Design - Based on the following design criteria:

Post- release flowrate < or = Pre-development flowrate at 2-yr and 10-yr ∙An emergency spillway that can safely pass the 100-year storm(or local standard) with 1 foot of freeboard.

3.Erosion and Sedimentation Control

∙Erosion protection measures should be utilized to stabilize inflow and outlet structures, including channels.