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Detention pond is one of the practises for stormwater management. It is used to control the stormwater discharge by temporarily storing the water and gradually releasing it by using a control outlet. Ponds can be developed as dry or wet ponds. 

 

DRY AND WET POND 

Dry Pond is also known as detention pond. It is a stormwater facility which temporarily holds the water and gradually releases it with no permanent pool of water. The discharge relies on the outlet control at the minor outlet design and located at the basin invert level. 

Dry detention pond in Klinik Kesihatan Taiping (from Google)

Wet Pond, sometimes called a retention pond, is a stormwater management facility which controls the water discharge before releasing it to the stream and retains a certain depth of water in the facility. According to MSMA, it is commonly designed for a catchment greater than 10 ha. 

Wet Pond in REDAC Universiti Sains Malaysia

 

HOW TO DESIGN DRY AND WET POND BY USING MiTS

Dry and wet ponds depend on the placement of the outlet control, such as orifice, at minor design. The height between the bottom orifice and the pond invert level is assigned in the minor design section, which indicates the depth of water retained.

 

i) Dry Pond

Dry pond consists of orifice which is located at the bottom of the basin and does not have a permanent pool of water. To indicate the height, insert 0 m at the H in MiTS in the Outlet Design tab, which denotes no water is retained. 

0 m H for the dry pond, 25 m is the pond invert level

Given the example above, the pond invert level is 25 m, therefore the Starting Water Level starts at 25 m, indicating that the pool routing starts from the pond invert level. 

 

ii) Wet Pond

Wet pond consists of orifice which is located higher than the pond invert level. Therefore, to indicate it in the MiTS, insert the permanent depth as in the highlight below. 

0.5 m H indicates 0.5 m permanent water depth, with 25.5 m starting water level

Default calculation of the Starting Water Level is the H + Invert Level, explaining that the pool routing starts at 25.5 m.

However, there are some situations whereby the Starting Water Level starts at the invert level (invert level 25 m) – dry pond, regardless of the H. For instance, when the retention pond is designed before any water is being discharged into the retention pond. For further details, you may visit this article (Starting Water Level for Retention Pond