Regionalized Equations for Bankfull-Discharge and Channel Characteristics of Streams
in New York State: Hydrologic Region 7 in Western New York
by Christiane I. Mulvihill, Anne G. Ernst, and Barry P. Baldigo
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006-5075
ABSTRACT
Computation of bankfull discharge and channel
dimensions (width, depth, and cross-sectional area) at ungaged sites requires
equations that relate bankfull discharge and channel dimensions to drainage-area
at gaged sites. Bankfull-channel information commonly is needed for watershed
assessments, stream channel classification, and the design of stream-restoration
projects. Such equations are most accurate if they are derived on the basis of
data from streams within a region of uniform hydrologic, climatic, and
physiographic conditions and applied only within that region. New York State
contains eight hydrologic regions that were previously delineated on the basis
of high-flow (flood) characteristics. This report presents drainage areas and
associated bankfull characteristics (discharge and channel dimensions) for
surveyed streams in western New York (Region 7).
Stream-survey data and discharge records from seven active and three inactive
USGS streamflow-gaging stations were used in regression analyses to relate
drainage area to bankfull discharge and to bankfull channel width, depth,
and cross-sectional area. The resulting equations are:
bankfull discharge (ft3/s) = 37.1*(drainage area, in mi2)0.765;
bankfull channel width (ft) = 10.8*(drainage area)0.458;
bankfull channel depth (ft) = 1.47*(drainage area)0.199; and
bankfull channel cross-sectional area (ft2) = 15.9*(drainage area)0.656.
The coefficients of determination (R2) for these four equations
were 0.94, 0.89, 0.52, and 0.96, respectively. The high coefficients of
determination for three of these equations (discharge, width, and
cross-sectional area) indicate that much of the range in the variables
was explained by the drainage area. The low coefficient of determination
for the equation relating bankfull depth to drainage area, however,
suggests that other factors also affected water depth. Recurrence intervals
for the estimated bankfull discharge of each stream ranged from 1.05 to 3.60
years; the mean recurrence interval was 2.13 years. The 10 surveyed streams
were classified by Rosgen stream type; most were C- and E-type, with occasional
B- and F-type cross sections. The equation (curve) for bankfull discharge
for Region 7 was compared with those previously developed for four other
hydrologic regions in New York State. The differences confirm that the
hydraulic geometry of streams is affected by local climatic and
physiographic conditions.
Citation: Mulvihill, C.I., Ernst, A.G., and Baldigo, B.P., 2006, Regionalized
Equations for Bankfull-Discharge and Channel Characteristics of Streams in New York State:
Hydrologic Region 7 in Western New York: U.S. Geological Survey Scientific Investigations
Report 2006-5075, 14 p., online only.
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