1. City Council March 4, 2014

3. Introduction The UCRA recommends the development of a storm water storage basin just to the east of FM 1223, south of Avenue L, and west of South Concho River for water quality, municipal water supply, and downstream release requirements in San Angelo, Texas. The basin will be located at the downstream end of the watershed drained by Red Arroyo, a tributary channel of South Concho River. This presentation summarizes the results of a completed feasibility study of the proposed storm water storage basin.

4. Hydrology – How much water Texas Institute for Applied Environmental Research (TIAER) developed a hydrologic model of Red Arroyo Watershed utilizing EPA SWMM (Feb 2013) Estimates of runoff rates and volumes for four relatively recent storm events were made from the modeling o Aug 2011: 3.74” Rainfall o Oct 2011: 2.71” Rainfall o Jan 2012: 1.67” Rainfall o March 2012: 0.74” Rainfall

5. Rainfall Analysis 95 th percentile rainfall depth represents a precipitation amount that is not exceeded by 95% of the rainfall events that occurred during the period of record. 95 th percentile 24-hour rainfall depth is estimated to be 1.67" This rainfall event yields 1007 acre-feet of runoff from the watershed.

6. Red Arroyo Watershed

7. Approximately 11,550 acre- feet will be captured by the basin in an average rainfall year. Water Availability

8. 3 options were evaluated for transferring the stored water to the WTP o Gravity flow system o Combined gravity flow and pump system o Pump flow Recommend a pump flow system from basin to WTP The basin can be emptied over a two week period with a flow rate of 20 MGD Conveyance to WTP Spoil Area

9. Opinion of probable cost

10. Additional Issues to Consider Water Rights Issues Section 404 Permitting from the US Army Corps of Engineers. Property Acquisition (Appraised Value $309,000)

11. The concept of a storm water storage basin to supply water to the water treatment plant is feasible. Excavation costs drive the total cost of the project. The cost scenarios evaluated in this report depend on a short haul distance for the basin excavation.Conclusions

12. Questions?