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    Author(s): Peter H. Cafferata; Leslie M. Reid
    Date: 2017
    Source: Gen. Tech. Rep. PSW-GTR-258. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 175-186
    Publication Series: General Technical Report (GTR)
    Station: Pacific Southwest Research Station
    PDF: Download Publication  (496.0 KB)


    Long-term flow records from sub-watersheds in the Caspar Creek Experimental Watersheds were used to test the accuracy of four methods commonly used to estimate peak flows in small forested watersheds: the Rational Method, the updated USGS Magnitude and Frequency Method, flow transference methods, and the NRCS curve number method. Comparison of measured and calculated results for 10-year return-interval flows demonstrates that, under the conditions tested, the direct flow transference method provides the most reliable results if suitable data are available; results for 100-year flows show similar patterns. None of the methods consistently underestimated the values derived from the gaging record. This indicates that these methods are unlikely to result in an under-design of drainage structures with respect to flow capacity. However, design of stable stream crossings in steep forested areas also requires consideration for passage of sediment, woody debris, and fish, so estimation of required flow capacity represents only a first step in the design process.

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    Cafferata, Peter H.; Reid, Leslie M. 2017. Using Caspar Creek flow records to test peak flow estimation methods applicable to crossing design. In: Standiford, Richard B.; Valachovic, Yana, tech cords. Coast redwood science symposium—2016: Past successes and future direction. Proceedings of a workshop. Gen. Tech. Rep. PSW-GTR-258. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 175-186.


    culvert sizing, flow estimation methods, forest hydrology, watercourse crossings

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