Quantitative Comparison on the Performance of an Infiltration Drain System

Abstract

Introduction Low Impact Development (LID) is an alternative approach in managing stormwater runoff. Its main philosophy is to replicate the pre-development hydrological properties of water catchment. It seeks to first infiltrate, filter, store and retaining the surface runoff near to its source before draining it to downstream. Some of the common LIDs include green roofs, permeable pavement, vegetated swales, infiltration drains, bioretention cells (also known as rain gardens). While LID seems to be a viable solution to reduce the flooding problem, we would like to investigate its performance after the LID (in particular infiltration drain system) has been put into operation for some time. A case study in Prinsejagt, Eindhoven will be used as data from previous studies is available to allow for comparison on the performance of infiltration drains after ~10 years of installation. Problem definition Infiltration drain has been used in Netherlands quite extensive, it is important to find out its current performance after years of operation. Existing researches or studies of infiltration drain system concentrate on its performance when it is newly installed. Studies that look into performance of an existing system which has been put into operation for quite some time are still quite rare. Research My research focused on determining the percentage reduction in exfiltration rate at the measurement site as compared to initial readings derived from previous research. It involves the monitoring of water levels at the same locations of the infiltration (IT) drain system in Prinsejagt (as carried out the previous monitoring scheme in 2003) and to carry out IT drain model simulations. In addition, we also conducted closed-loop test at four selected stretches of infiltration pipes to ascertain the exfiltration properties of the particular stretch of pipe. First, we seek to explain the phenomenon observed at our monitoring site qualitatively before applying quantitative approaches (like graphical, curve-fitting and simulation methods) to assess the percentage reduction in exfiltration rates at the monitoring locations. Based on the projected clogging rate, simulations were carried out to predict the future system exfiltration rate. Results 1. System behaviour (of the IT drains network) coupled with the influence of groundwater level determine the overall performance of the IT drain system. 2. Individual IT pipes exhibit more varied rates of exfiltration (due to different localized conditions) 3. Verified that linear mathematical function can adequately describe the water level trends to an accuracy of 0.01m RMSE for all monitoring locations 4. Observed a 9.4% drop in exfiltration rate [L3/T] in the IT drain model. By 2021, the exfiltration rate is expected to drop by 20% from its starting value. Conclusions and recommendations Regular maintenanceto clear the accumulated sediment inside IT drains and thereafter monitoring of performanceshould be carried out so as to determine its effectivenessin increasing the overall permeability.Moreover, water quality monitoring in IT drain system could be implemented to prevent any contamination to groundwater resources. In lowering the pipe invert level of the entire IT system, the IT system performance can be enhanced during low groundwater period.