Stormwater Runoff Modelling in an Urban Catchment to Plan Risk Management for Contaminant Spills for Stormwater Harvesting

Water quality is a key consideration for urban stormwater harvesting via aquifers. This study assessed catchment spill management options based on a calibrated dynamic wave routing model of stormwater flow in an urban catchment. The study used measured travel times, pluviometer and gauging station observations from 21 storms to calibrate a stormwater model to simulate transport of pollutants from spill locations to the point of harvest. The simulations considered the impact of spill locations, spill durations, storm intensities and storm durations on the pollutant concentration at the point of harvest and travel time of a pollutant spill to the harvesting point. During dry weather, spill events travelled slower than spills occurring during wet weather. For wet weather spills, the shortest travel times tended to occur in higher intensity storms with shorter duration, particularly when a spill occurred in the middle of the storm. Increasing the intensity of rainfall reduced the peak concentration of pollutant at the harvest point via dilution, but it also reduced the time of travel. On a practical level, due to the short response times in urban catchments, management of spills should be supported by automated detection/diversion systems to protect stormwater harvesting schemes.

Stormwater harvesting in ephemeral streams: how to bypass clogging and unsaturated layers

To cope with water scarcity in drylands, stormwater is often collected in surface basins and subsequently stored in shallow aquifers via infiltration. These stormwater harvesting systems are often accompanied by high evaporation rates and hygiene problems. This is commonly a consequence of low infiltration rates, which are caused by clogging layers that form on top of the soil profile and the presence of a thick vadose zone. The present study aims to develop a conceptual solution to increase groundwater recharge rates in stormwater harvesting systems. The efficiency of vadose-zone wells and infiltration trenches is tested using analytical equations, numerical models, and sensitivity analyses. Dams built in the channel of ephemeral streams (wadis) are selected as a study case to construct the numerical simulations. The modelling demonstrated that vadose-zone wells and infiltration trenches contribute to effective bypassing of the clogging layer. By implementing these solutions, recharge begins 2250–8100% faster than via infiltration from the bed surface of the wadi reservoir. The sensitivity analysis showed that the recharge rates are especially responsive to well length and trench depth. In terms of recharge quantity, the well had the best performance; it can infiltrate up to 1642% more water than the reservoir, and between 336 and 825% more than the trench. Moreover, the well can yield the highest cumulative recharge per dollar and high recharge rates when there are limitations to the available area. The methods investigated here significantly increased recharge rates, providing practical solutions to enhance aquifer water storage in drylands.

A study on the effectiveness of percolation ponds as a stormwater harvesting alternative for a semi-urban catchment

One of the challenges in urban stormwater management is to identify a suitable stormwater management method which will be socially, technologically and economically viable. In this paper, a study on the effectiveness of decentralized and interconnected percolation ponds as a stormwater harvesting technology, for a partially urbanized (semi-urban) catchment is presented. When applied to a case study region in Katpadi, Tamil Nadu, the results were encouraging. The investment required for implementing the proposed stormwater harvesting came to be about 555 Million for Option I and 714 Million for Option II. The annual volume of water that can be added to the groundwater system through infiltration from the ponds was found to be 1.22 Mm3 in the case of Option I and 0.74 Mm3 in the case of Option II. The percentage area under stormwater harvesting for the entire catchment was found to be 6.14% under Option I and 9.36 under Option II. The hydrologic performance of the proposed stormwater harvesting system indicated that for peak runoff values Option II is more efficient (in terms of minimizing runoff volume) compared to Option I; however, for daily rainfall values, Option I is hydrologically more efficient when compared to Option II.

Stormwater harvesting infrastructure systems design for urban park irrigation: Brimbank Park, Melbourne case study

Stormwater harvesting for residential and non-residential reuse is an important and crucial aspect to reduce freshwater demand to address climate change, population growth and urbanisation challenges. It is important that freshwater be conserved as much as possible through capturing rainwater and stormwater and using these resources for fit for purpose end uses such as irrigation of public open parks and residential non-potable end uses. The paper describes a methodology for the planning and design of a stormwater harvesting system for park irrigation. The application of suitable models for storage tank capacity and pipe sizing considering peak flows are described. The application of the approach is demonstrated with a local case study for the benefit of wider water professionals engaged in water-sensitive urban design.

Water quality performance of a permeable pavement and stormwater harvesting treatment train stormwater control measure

Stormwater runoff from urban development causes undesired impacts to surface waters, including discharge of pollutants, erosion, and loss of habitat. A treatment train consisting of permeable interlocking concrete pavement and underground stormwater harvesting was monitored to quantify water quality improvements. The permeable pavement provided primary treatment and the cistern contributed to final polishing of total suspended solids (TSS) and turbidity concentrations (>96%) and loads (99.5% for TSS). Because of this, >40% reduction of sediment-bound nutrient forms and total nitrogen was observed. Nitrate reduction (>70%) appeared to be related to an anaerobic zone in water stored in the scarified soil beneath the permeable pavement, allowing denitrification to occur. Sequestration of copper, lead, and zinc occurred during the first 5 months of monitoring, with leaching observed during the second half of the monitoring period. This was potentially caused by a decrease in pH within the cistern or residual chloride from deicing salt causing de-sorption of metals from accumulated sediment. Pollutant loading followed the same trends as pollutant concentrations, with load reduction improved vis-à-vis concentrations because of the 27% runoff reduction provided by the treatment train. This study has shown that permeable pavement can serve as an effective pretreatment for stormwater harvesting schemes.

Hydrophilic trace organic contaminants in urban stormwater: occurrence, toxicological relevance, and the need to enhance green stormwater infrastructure

Urban stormwater transports hydrophilic trace organic contaminants that need study to ensure safe stormwater discharge or stormwater harvesting for water supply.