Showing papers by "Tim D. Fletcher published in 2021"

Enhancing stormwater control measures using real-time control technology: a review

Abstract: Stormwater Control Measures (SCMs) are increasingly applied to capture and utilise urban runoff to augment water supply, reduce flood risk, and to restore natural flow regimes in receiving waters. ...

Modeling bioretention stormwater systems: Current models and future research needs

Abstract: Many bioretention models still incorporate simplifications and lumped parameters that do not fully account for fundamental physical processes. This review summarizes the representation of hydrologic pathways, notable features, and applications of bioretention models with the goals of recommending models well suited to bioretention modeling and identifying key research needs. As a result, HYDRUS and GIFMod were identified as the only models that use Richards’ equation for determining infiltration under variably saturated conditions. Secondly, this study identified limited drainage configurations by most models except DRAINMOD-Urban. Thirdly, most models were inadequate for considering vegetation and plant water use, an area for improvement in future research. Finally, more calibration and validation studies are needed to build confidence in model results. This review intends to educate modelers of the processing equations for each water balance component, the input requirements in each model, and other model characteristics that should be considered in model selection.

Understanding the Impact of Soil Clay Mineralogy on the Adsorption Behavior of Zinc

Abstract: Infiltration systems are increasingly used to reduce peak flows and mitigate the impacts of stormwater runoff. Despite the benefits of infiltration systems, there is a risk for associated pollutants, including heavy metals to be introduced to the underlying soil and groundwater. The subsequent movement of metals in the subsurface and their potential to contaminate water resources is uncertain and profoundly depends on the adsorptive behavior of the surrounding soil. We used two soil types, one natural (quartz–kaolinite–muscovite) and one synthetic (quartz and kaolinite only) with different clay mineralogy to test their potential adsorptive capacities through batch systems, with Zn(II) as a representative tracer. Nonlinear isotherms, Freundlich and Langmuir, provided good fits with the experimental sorption data. Kinetic data were well fitted by a pseudo-second-order model, indicating that cation exchange exists between the clay surfaces and Zn(II) in the liquid phase. We found that the natural soil adsorbed far more Zn(II) when compared to the synthetic soil which was attributed to the presence of the muscovite in the natural soil. Comparison of the observed adsorption capacity of the two soils with their predicted adsorption capacities showed that while the adsorption capacities of the single-sized clay minerals are widely reported, these values cannot be linearly extrapolated to estimate the adsorption capacity of a soil that might contain varied fractions of clay. The results suggest that the designers of infiltration systems should first undertake an analysis of clay mineralogy of the subsurface soil to better predict the fate of heavy metals within the surrounding soils.

Impacts of stormwater infiltration on downslope soil moisture and tree water use

Abstract: Infiltration of stormwater is a widely used strategy to mitigate the flooding and environmental risks that come from urban runoff and conventional urban drainage. An understanding of the fate of this infiltrated water is required for rigorous design. Principal design objectives are typically to restore more natural hydrology in order to protect receiving waters from pollution and hydrologic change. Without such understanding there is also a risk of unforeseen impacts on nearby infrastructure and urban vegetation. We sought to understand the pathways and fate of water from a stormwater infiltration basin. To trace water, we used a combination of water table monitoring and isotopic composition analysis in the infiltration basin, as well as in rainfall, soil water, the shallow groundwater, and in vegetation upslope and downslope of the basin. We also measured tree water use directly using sap flow sensors. The infiltration basin was shown to increase the availability of water downslope, allowing trees to maintain elevated levels of water use during dry periods with high energy demand. In contrast, water limitation upslope saw substantial seasonal reductions in tree water use. The soil water isotopic composition demonstrated significant differences from upslope to downslope, with downslope water being more reflective of rainfall, while the upslope water used by the trees was more depleted. The results paint a picture of stormwater infiltration being a significant source of lateral flow, while trees are a significant sink of lateral flow emanating from the basin. This finding suggests that stormwater infiltration could be used as a strategy to support the health and growth of urban trees. Urban trees have demonstrated benefits for human health and comfort, particularly in a warming climate. It also suggests that stormwater infiltration may not always recharge groundwater and provide baseflow in receiving waters, being instead taken up by vegetation. These findings should be considered in the siting of stormwater infiltration systems, to ensure that the objectives they were designed for are actually met.

Modelling uniform and preferential flow in bioretention systems

Abstract: Bioretention systems are increasingly used worldwide to mitigate the impacts of urban stormwater runoff on the water cycle. The proper management of bioretention systems requires accurate modeling of physical processes occurring within these systems. This study developed and tested a generic and physically-based model called Infiltron-mod. This model makes use of the Darcian approach (assuming Mualem-van Genuchten model for the description of the soil hydraulic properties) and mass conservation. The first version of the model considers evapotranspiration, overflow, exfiltration to surrounding soils, along with the filter hydraulic head and underdrain discharge. The proposed model was tested against field data from a monitored bioretention basin in Melbourne, Australia. We used two rainfall events to calibrate the model and 20 rainfall events for its validation. We achieved quite nice fits of experimental data with median NSE values in the order of 0.7-0.75 for the outflow rates. Despite good performance for outflow rates, we noticed the potential for improvement for the simulation of the height of water in the systems. Such discrepancy is probably the result of preferential flows.