Design and development of a novel automated runoff simulator system

Rainfall simulators, whether based within a laboratory or field setting, have been used extensively for a variety of hydrological, geomorphological and engineering-based research applications. Rainfall and runoff processes are often investigated together, with runoff regimes being a key component of the hydrological cycle. Rainfall simulators are well documented research apparatus. However, few published examples of an experimental setup capable of applying simulated and controlled artificially irrigated ‘runoff’ exist in the literature. This paper presents the design, construction and evaluation of a novel experimental runoff simulator (as opposed to a rainfall simulator) setup capable of augmenting and upscaling inflow precipitation from natural rainfall events and applying additional ‘top-up’ volumes of water to account for runoff received from a wider catchment area and applying artificial storm events of controlled magnitude and timing. Runoff simulators were installed on eight above ground lysimeter bioretention cells (1.0 m × 2.0 m surface area, 1.2 m deep soil profile) based at the UKCRIC National Green Infrastructure Facility, Newcastle-upon-Tyne, UK. The runoff simulators have two primary functions. Firstly, the runoff simulators work in near real-time to upscale natural plot-scale precipitation data, recorded directly at each of the rain gauges fitted to the lysimeters, and incorporate a series of solenoid valve relays and turbine flow sensors to initiate, measure and isolate irrigation scheduling based on runoff received from an adjacent urban impervious surface or pavement. Secondly, the runoff simulators are used to apply controlled and uniform ‘design storm’ events of known intensities to simulate the response of the lysimeter systems to inflow conditions outside of the instrumented record. Data showing replicability and reproducibility of set inflow patterns are presented. Further, results from design storm events of varying magnitude (10-year, 30-year and 100-year storm magnitude) show the functionality of the runoff simulators and the response of the lysimeters to simulated inflows. Rainfall and runoff processes should both be considered when undertaking hydrological experiments. The runoff simulator presented herein is adaptable to a variety of research applications and could be coupled with rainfall simulator piping to apply spatiotemporal design storms and automate the delivery of plot-scale irrigation to plot-scale experiments.