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ROAD DRAINAGE DITCH DESIGN PARAMETERS AND RESULTS: <br />• Road Drainage Ditch Section 1 <br />Design Parameters: <br />Precipitation: <br />Use 10-year, 24-hour storm precipitation depth = 1.8 in <br />Land Use: <br />Contributing azeas (3.55 ac): <br />Stru#1 SWS#1 = 0.22 ac with CN = 98 (paved parking lot) <br />Stru#1 SWS#2 = 0.36 ac with CN = 89 (newly graded, no <br />vegetation -hydrologic soil group B-C) <br />Stru#1 SWS#3 = 0.90 ac with CN = 98 (paved parking lot) <br />Stru#1 SWS#4 = 2.07 ac with CN = 63 (sagebrush -hydrologic <br />soil group C) <br />Ditch grade = 5.1 <br />Ditch length = 530 feet <br />Ditch design =triangular ditch (see Figure 2) <br />Ditch surface material is graded silts to cobbles when colloidal <br />Limiting ditch velocity = 4.0 fps <br />Results: <br />Peak flow = 1.84 cfs <br />Peak velocity = 3.85 fps <br />• Road Drainage Ditch Section 2 <br />Design Pazameters: <br />Precipitation: <br />Use 10-yeaz, 24-hour storm precipitation depth = 1.8 in <br />Land Use: <br />Contributing areas (6.13 ac): <br />Stru#1 combined area = 3.55 ac (see breakdown above for ditch <br />Section 1) <br />Stru#2 SWS#1 = 1.88 ac with CN = 63 (sagebrush -hydrologic <br />soil group C) <br />Stru#2 SWS#2 = 0.70 ac with CN = 98 (gravel road) <br />Ditch grade = 13.0 <br />Ditch length = 543 feet <br />Ditch design =triangular ditch (see Figure 3) <br />Ditch surface material is graded silts to cobbles when colloidal <br />Limiting ditch velocity = 4.0 fps <br />Results: <br />Peak flow = 2.78 cfs <br />Peak velocity = 4.56 fps (exceeds limiting velocity, therefore riprap required) <br />Riprap design: Drain ° 2:0 in, D50-° 3:0"iri,-Dmax = 4.5 in- <br />• <br />