Numerical simulation of conventional and staggered dry ponds for stormwater management

Abstract

Conventional dry ponds are typically constructed as single ponds featuring a fixed-size orifice outlet at the end. This design inherently maintains a high water stage which severely limits the pond's dynamic storage capacity and resilience to increasing runoff from climate change. This paper presents a case study investigating the hydraulic performance of novel staggered dry pond designs. The modification involved strategically staggering an 80 m long dry pond into two smaller, interconnected ponds using a second internal restriction, outlet 1. Three design scenarios were simulated by placing outlet 1 at varying distances from the inlet (20 m, 40 m, and 60 m). The performance of outlet 1 was further assessed across a wide range of orifice diameters (0.1 m to 0.8 m), while the original discharge orifice, outlet 2, was maintained. A Storm Water Management Model was utilized to simulate and compare the conventional and staggered pond characteristics. The results showed that the upstream ponds consistently maintained high flows and stages, similar to the conventional pond. However, the downstream basins exhibited dramatically different, desirable hydraulic patterns. Peak flows in the downstream segments were significantly attenuated, reducing from a maximum of 2.0 m3/s (upstream) to below 1.0 m3/s. The stage reduction was highly sensitive to the size of outlet 1. Optimal diameters (0.1 m to 0.4 m) reduced the downstream stage by more than 50% (to 0.7 m or less) compared to the maximum 1.4 m stage. This staggered design offers a viable and practical engineering solution for enhancing the flood mitigation capacity of existing dry ponds.