Abstract
The influence of long-term suspended sediment dynamics on stormwater pond performance should not be ignored, but is often neglected in pond design and performance evaluation. This paper provides systematic simulated quantification of long-term suspended sedimentological effects on stormwater pond performance. Integrated hydrological and two-dimensional hydro-morphodynamic modelling and simulations were carried over a 32-year period (1984–2015) covering 3896 rainfall events with a wide range of rainfall volumes, durations and intensities. Three event-based hypothetical rainfall scenarios: non-flood condition (5-year), sewer design condition (30-year), and river flood condition (100-year) rainfall events with 1-h duration, were also simulated for comparison between the traditional event-based approach and the novel approach presented in this study. Simulation results show that the flood peak attenuation and delay are more pronounced for small (<5-year) and medium (<30-year) flood events. The long-term continuous simulation results indicate that the pond provides positive annual trap efficiencies varying from 2% to 69% for 31 of 32 years, providing long-term water quality benefits downstream. However, an extreme rainfall event in year 2012 flush out the accumulated sedimentation as a shock load to the downstream river, leading to a negative trap efficiency of −11%. The spatially averaged sediment deposition rate, as predicted by the model, varies with a mean (SD) of 2 (1.34) cm/year over the study period, which resulted in a 24% loss in the pond’s volume over 32 years. The impact of the loss in storage on pond flood attenuation capacity are explored at regular time intervals over the study period. The results indicate that reduction in the pond’s flood attenuation capacity is relatively more pronounced for medium (30-year) and extreme (100-year) flood events than the frequent small flood (5-year) events. The variation in annual sediment loading with rainfall quantities and patterns are also explored.
Highlights
1.1 Background In recent years, stormwater ponds (a.k.a. retention ponds, wet ponds, wet extended detention ponds) are increasingly being regarded as the promising option for stormwater management (Lawrence et al, 1996; Krishnappan and Marsalek, 2002; Biggs et al, 2005) in the UK and many other countries
Hydrodynamic models, which are based on the deterministic solution of hydraulic equations (Bruen and Yang, 2006), can provide more insight into the physical processes that occur within the pond system
This study focuses on the impact of a specific pond (Figure 2a) on long-term flow characteristics and suspended sediment dynamics
Summary
1.1 Background In recent years, stormwater ponds (a.k.a. retention ponds, wet ponds, wet extended detention ponds) are increasingly being regarded as the promising option for stormwater management (Lawrence et al, 1996; Krishnappan and Marsalek, 2002; Biggs et al, 2005) in the UK and many other countries. Excess sedimentation in urban rivers may lead to a number of adverse ecological and environmental consequences as the loading of suspended sediment from an urban environment is significantly higher than that in rural catchments (Arias et al, 2013; Poleto et al, 2009) This is because increased impermeable surfaces in the urban environment shield and arrest sources of coarse material and disproportionally increase fine materials in stormwater runoff (Brodie and Dunn, 2009; Savage, 2005). Pollutants and coliform bacteria which are generated from the urban environment and transported by storm runoff (Jartun et al, 2008). These stresses the biological, chemical and physical integrity of the receiving water through eutrophication, toxification, limited permeability and reduced oxygen delivery. Contaminants associated with suspended sediment particles and dissolved solutes in stormwater runoff are rather difficult to manage than coarse particles (Birch et al, 2006)
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