Regionalized equations for bankfull-discharge and channel characteristics of streams in New York State — Hydrologic Region 3 east of the Hudson River

Equations that relate drainage area to bankfull discharge and channel characteristics (such as width, depth, and cross-sectional area) at gaged sites are needed to define bankfull discharge and channel characteristics at ungaged sites and can be used for stream-restoration and protection projects, stream-channel classification, and channel assessments. These equations are intended to serve as a guide for streams in areas of similar hydrologic, climatic, and physiographic conditions. New York State contains eight hydrologic regions that were previously delineated on the basis of high-flow (flood) characteristics. This report presents predictive equations for bankfull characteristics (discharge and channel characteristics) for streams east of the Hudson River, referred to as Hydrologic Region 3.

Stream-survey data and discharge records from 12 streamflow-gaging stations were used in regression analyses to relate drainage area to bankfull discharge and bankfull channel width, depth, and cross-sectional area. The four predictive equations are:

(1) bankfull discharge, in cubic feet per second = 83.8*(drainage area, in square miles)^0.679;

(2) bankfull channel width, in feet = 24.0*(drainage area, in square miles)^0.292;

(3) bankfull channel depth, in feet = 1.66*(drainage area, in square miles)^0.210; and

(4) bankfull channel cross-sectional area, in square feet = 39.8*(drainage area, in square miles)^0.503.

The coefficients of determination (R²) for these four equations are 0.93, 0.85, 0.77, and 0.92, respectively. The high coefficients of determination for bankfull discharge and cross-sectional area indicate that much of the range in the variables is explained by the size of the drainage area; the smaller correlation coefficients for bankfull channel width and depth indicate that other factors also affect these relations. Recurrence intervals for the estimated bankfull discharge of each stream ranged from 1.16 to 3.35 years; the mean recurrence interval was 2.08 years. The 12 surveyed streams were classified by Rosgen stream type; most were B and C type, with occasional E- and F-type cross sections. The Region 3 equation (curve) for bankfull discharge was compared with those previously obtained for seven other hydrologic regions in New York State. The differences confirm that the hydraulic geometry of streams is affected by local climatic and physiographic conditions.