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Rainwater Harvesting Legal Framework Page S Measurements of infiltration using a Simulate surface runoff for each storm using Denver lysimeter, and measurements of Urban Drainage and Flood Control District's runoff, to the extent possible', Colorado Unit Hydrograph Procedure (CUHP) model through surface water measurement. or another model such as WQ-COSMs using 15 -minute precipitation data. Calibrate simulation to lysimeter and other on-site measurements. Precipitation - Simulated Runoff = Infiltration Soil Moisture Balance Measurement of soil moisture in the For the water that infiltrates, there is a water lysimeter. budget accounting where soil moisture may be consumed by ET and where any water in excess of the soil moisture capacity is assumed to deep percolate and slowly return to the stream system. This analysis will inform how infiltration on the site is partitioned to historic natural depletion vs. deep percolation to ground water return flow to the stream system. Ground Water Return Flows None Groundwater modeling or lagging calculations estimate the delay of deep percolation to surface water. Rainwater harvesting projects must install a high quality precipitation gage that records data at a 15 -minute frequency and can provide that data for use in daily accounting. If Factors are not used, it may be necessary to install a lysimeter to measure infiltration and deep percolation in the native condition. A lysimeter allows for the direct calculation of historic natural depletion. Since the data collection phase occurs when the harvesting system is in place, but the historic natural depletion is based on the native condition, a lysimeter must be placed in an area of the development that is preserved in its undisturbed natural condition. This will allow data collection of the soil water balance and historic natural depletion under a range of storm conditions that occur during the two-year data collection phase, while full replacement of captured rainwater is made to the stream. The SWSP application will need to provide the following: Information Related to Historic Natural Depletion (may not all be required if Factors are used): 1. Describe and map instrumentation associated with measuring historic natural depletion in relation to the location of the rainwater harvesting system: rain gage (minimum 15 -minute frequency), lysimeter, and surface flow measurement, if any. 8 Measurements of surface runoff on Sterling Ranch have been difficult to calibrate to precipitation and lysimeter observations and modeling.