Nor Aqilah Bt Othman

1. Nor aqilah bt othman 55102215008
RETENTION BASIN

2. Retention basin
• manage storm water runoff to prevent flooding and downstream
erosion, and improve water quality in an adjacent river, stream, lake
or bay.
• act as a replacement for the natural absorption of a forest or other
natural process that was lost when an area is developed.
• to contain surge and release it slowly. This slow release mitigates
the size and intensity of storm-induced flooding on downstream
receiving waters.

3. In Out
Precipitation,Freshwater, Freshwater,TreatedWater

4. In this illustration of a typical storm water system, as the water rises, sediment
and pollutants — such as bacteria and heavy metals — picked up on the way
to the pond sink to the bottom. The outflow structure usually has a small pipe
or opening that sits just above the normal water level. When the water level
reaches the outflow structure, the treated water will begin flowing out of the
pipe. Not all systems work exactly in this way, but this is a standard design for
wet detention ponds.

5. Working Principle
Surface run-off is stored permanently in ponds,
allowing increased storm water management and
quality enhancement through natural processes.
Capacity/Adequacy
Retention basins require a large area of land and
are only applicable to areas with high rainfall and
enough free space.
Performance
Retention basins filter pollutants such as
metals, nutrients, sediments, or organics
by sedimentation. Further removal of pollutants is
achieved through algal and wetland plant uptake
as well as bacterial decomposition(EPA 1999)
Costs
High costs arise for the construction of retention
basins and the value of the land. Once in
operation, only minimal maintenance costs occur.
Self-help Compatibility
Construction requires expert design;
operation, monitoring and maintenance require
skilled staff.
O&M
Basins have to be cleared from excess sediment
and trash. Also, quarterly inspections of water in-
and outlets are needed.
Reliability
Reliability persistence of retention basins is very
high if well maintained, with a life span of usually
more than 20 years.
Main strength Floodwater can be controlled and water quality is
enhanced.
Main weakness
Large land areas need to be available to build
ponds; risk of uncontrolled reuse and mosquito
breading.