**Subject:** Detention Basin Basics in SWMM 5

What are the basic elements of a detention pond in SWMM 5? They are common in our backyards and cities and just require a few basic elements to model. Here is a model in SWMM 5.0.022 that even has a fountain in the real pond – which we not model for now. The components of the model are:

1. An inlet to the pond with a simple time series – a subcatchment can be added to it in a more complicated model but for now we will just have a triangular time series,

2. A pipe to simulate the flow into the pond from the inlet,

3. A **Storage Node** to simulate the Pond that consists of a tabular area curve to estimate the depth and area relationship,

4. A **Storage Node** to simulate the Outlet Box of the Pond

5. Two Small Rectangular **Orifices** to simulate the low flow outflow from the pond at an elevation less than the weir

6. A large rectangular **orifice** to simulate the normal inflow to the Box

7. A rectangular weir to simulate the flow into the box when the pond water surface elevation is above the box

8. The outlet of the Box is a circular link with a Free outfall as the downstream boundary condition

9. The flow graph in the image shows the flow into the box starts from the two small orifices, next from the large orifice and finally from the top of the box or the weir.

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