Stormwater Manual - Pima County Flood Control District

Pump stream flow around the check dams.
discharge.
Install outlet protection as required at the
Dewater the work area and pump into a sediment trapping device.
Complete construction activities across the stream.
Restore the streambed and banks.
Remove sandbags and shut down pumping operation. (Salvage sandbags for future use if
multiple stream crossings are required on the project.) Remove all sandbags from the stream,
including damaged and empty bags.
Pumps shall be manned around-the-clock when the pump-around diversion is in the stream.
Maintenance
This control provides short-term diversion of stream flow (typically 1 day to 3 days).
Additional sandbags or pumps may be required to maintain 1-foot freeboard on the sandbag
checks if flow conditions change.
Add sandbags as required to seal leaks in checks.
11.5.9 Construction Dewatering
Dewatering is the pumping of stormwater or groundwater from excavation pits or trenches.
The sediment-laden water must be pumped to a dewatering structure before it is discharged
offsite. The purpose of a dewatering structure is to remove sediment from the water before it
is discharged.
Design Criteria
There are several types of dewatering structures that may be used. A well-stabilized
vegetated area may serve as a filtering structure if it can withstand the velocity of the
discharged water. The minimum filter length must be at least 75 feet.
Other methods that may be used include a sediment trap/basin, portable sediment tank, a
straw bale/silt fence pit, or a commercial sediment filter bag. The structure must be sized to
allow pumped water to flow through the structure without overtopping.
Construction Specifications
See the specifications in this manual for sediment traps and basins. The manufacturer’s
recommendations should be followed for commercial products.
Maintenance
The dewatering structure should be inspected frequently to ensure it is functioning properly
and not overtopping. Accumulated sediment should be spread out on site and stabilized, or
disposed of offsite.
STORMWATER MANUAL 11-48 August 29, 2011
LEXINGTON-FAYETTE CO., KY.