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VI. Avoided Runoff <br />Surface runoff can be a cause for concern in many urban areas as it can contribute pollution to streams, wetlands, <br />rivers, lakes, and oceans. During precipitation events, some portion of the precipitation is intercepted by vegetation <br />(trees and shrubs) while the other portion reaches the ground. The portion of the precipitation that reaches the <br />ground and does not infiltrate into the soil becomes surface runoff (Hirabayashi 2012). In urban areas, the large <br />extent of impervious surfaces increases the amount of surface runoff. <br />Urban trees and shrubs, however, are beneficial in reducing surface runoff. Trees and shrubs intercept precipitation, <br />while their root systems promote infiltration and storage in the soil. The trees and shrubs of City of Pleasanton help <br />to reduce runoff by an estimated 1.43 million gallons a year with an associated value of $13 thousand (see Appendix I <br />for more details). Avoided runoff is estimated based on local weather from the user -designated weather station. In <br />City of Pleasanton, the total annual precipitation in 2021 was 15.2 inches. <br />C <br />O <br />200 <br />Gn <br />c <br />3 150 <br />O <br />Y <br />CO 100 <br />° <br />W <br />0 50 <br />0 <br />oto 4011 a�°� e°a� 5r� 6�7 If <br />Ile N <br />L L �r\tio� <br />(CA valley oak) species <br />e <br />`'b <br />e5�r La ��J <br />e <br />2500 <br />2000 <br />1500 <br />aj <br />1000 i <br />500 <br />0 <br />Figure 10. Avoided runoff (points) and value (bars) for species with greatest overall impact on runoff, City of <br />Pleasanton <br />Page 14 <br />76 of 219 <br />