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Published on: May 15, 2017
Retrofitting a stormwater retention pond using a deflector island
S Khan1, B W Melville, A Y Shamseldin
1Department of Civil and Environmental Engineering, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand. skha121@aucklanduni.ac.nz
Summary
Adding deflector islands to stormwater retention ponds may not improve sediment removal. This study found that islands can unexpectedly increase short-circuiting in ponds with sloping walls, reducing their effectiveness.
Area of Science:
- Environmental Engineering
- Hydraulic Engineering
- Water Quality Management
Background:
- Stormwater retention ponds are crucial for treating urban runoff and removing sediments.
- Residence time distribution (RTD) analysis is a key method for assessing pond efficiency.
- Deflector islands have been proposed to enhance pond performance by diffusing inlet jets.
Purpose of the Study:
- To investigate the impact of a deflector island on the hydraulic performance of a stormwater retention pond.
- To evaluate the effect of pond geometry, specifically sloping walls, on island performance.
- To analyze sediment removal efficiency using residence time distribution (RTD) curves.
Main Methods:
- A physical model of a trapezoidal stormwater retention pond with sloping walls (2:1 h:v) was constructed.
- Three different configurations were tested, including arrangements with a deflector island.
- Residence time distribution (RTD) curves were analyzed to assess hydraulic performance and flow patterns.
Main Results:
- The inclusion of a deflector island did not improve the pond's performance in terms of sediment removal.
- Instead, the deflector island was observed to stimulate short-circuiting, reducing the effective residence time.
- This outcome contrasts with previous studies, likely due to the novel inclusion of sloping walls in the model.
Conclusions:
- Deflector islands may not be universally beneficial for stormwater retention pond performance.
- The presence of sloping walls in retention ponds can significantly alter the hydrodynamics and the effectiveness of islands.
- Further research is needed to understand the complex interactions between island design and pond geometry for optimized stormwater treatment.
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