Updating Hydrologic Properties of Property‑Scale Subbasins: Post‑Construction Remeasurements for Tucson Water

Daniel Saavedra, Martha Whitaker

Tucson Water offers rebates to Tucson residents who build rainwater-harvesting subbasins that help sustain the region’s most valuable resource: water. This project focuses on improving Tucson Water’s understanding of the water volume these residential basins can capture and retain. The objective of this project is to remeasure the dimensions, fill capacity, and infiltration rate of residential basins to determine the accuracy of Tucson Water’s protocol for estimating basin capacity, and whether the estimates reflect the criteria for the rebate. For each participating property, the process was to measure basin length, width, and depth to calculate basin volumes. The next step was to measure pre-existing soil moisture using a TDR probe and collect soil samples to characterize soil particle size distribution.  Hoses delivered water to fill the basins at a specified rate, which allowed for estimates of storage capacity and infiltration rate. Our measurements showed that most subbasins have a larger effective volume capacity and infiltration rate than Tucson Water’s protocol estimates. These results suggest that Tucson Water’s protocol is sufficiently accurate to determine a resident’s eligibility for the rebate associated with building rainwater-harvesting basins on their property. These results also support continued promotion of rainwater-harvesting basins as a strategy to enhance local water availability and landscape health.