Drainage Design Manual - the City of San Luis Obispo

c. BrushMannings“n”Type of Channel & Description(Normal)2. Mature row crops 0.0353. Mature field crops 0.0401. Scattered brush, heavy weeks 0.0502. Light brush and trees 0.0603. Medium to dense brush 0.0704. Heavy, dense brush 0.100d. Trees1. Dense willows, straight 0.1502. Cleared land with tree stumps, no sprouts 0.0403. Same as above, but with heavy growth of sprouts 0.0604. Heavy stand of timber, a few down trees, little undergrowth,flood stage below branches0.1005. Same as above, but with flood stage reaching branches 0.12Source: “Open Channel Hydraulics”, V.T. Chow and King County Washington, Surface Water Drainage Manual, January 1990.TABLE 5-3Guide for Determining “n” ValuesFor Vegetation Management ClassesCLASSDESCRIPTION(WHR * CLASS)TYPICALDENSITYTREES/ACRETYPICALBASAL AREA/CANOPYCOVER“n” VALUE*1 Dense Thicket (Dense) 300-600+ BA > 100Cover 80-100%2 Closed Canopy(Dense) 200-400+ BA 50-100+Cover 80-100%3 Park-Like(Dense) 120-300 BA 30-50Cover 60-79%4 Moderately Dense (Moderate) 50-150 BA 20-30Cover 40-59%5 Savanna-Like (Open) 10-60 BA < 20Cover 25-39%6 Oak-Grassland (Sparse)