Low-flow hydraulic geometry of small, steep mountain streams in southwest British Columbia

Controls on at‐a‐station hydraulic geometry in steep headwater streams, Colorado, USA

“…The range of values found in Colorado was also similar to the range found by Reid (2005) for lower gradient step-pool, cascade and plane-bed reaches in British Columbia (Figure 4a), although there was a larger amount of scatter in Reid's data and the means differed (m = 0·51, f = 0·29, b = 0·20).…”

“…The AHG values found in this study are compared to Reid's (2005) study on streams in British Columbia. All three AHG exponents are interrelated; therefore, the ternary diagram has been found to be a useful format for investigating simultaneous variations in the exponents (Park, 1977;Rhodes, 1977).…”

“…An increasing width/ depth ratio with discharge means that the fl ow is primarily accommodated by an increase in width rather than an increase in depth in this reach. All reaches except ESL7 have m > f, which can be interpreted as increasing stream competence with increasing discharge (Rhodes, 1977;Reid, 2005), although this subdivision is related to low gradient streams and does not account for bed armoring in these higher gradient channels. ESL7 is the only reach that has depth increasing faster with discharge than velocity.…”

“…Leopold and Maddock (1953) found that the rates of change of width, depth and velocity with discharge were related to the shape of the channel, the slope of the watersurface and the roughness of the wetted perimeter. They also found the sediment load to be an important control on the rates of change of both velocity and depth (Leopold and Maddock, 1953).Few studies have reported AHG values for steep mountain channels (Lee and Ferguson, 2002;Reid, 2005;Comiti et al, 2007). A better understanding of at-a-station changes in each of the above hydraulic variables can improve our understanding of the sources and magnitude of hydraulic roughness in these channels, which tend to have values of fl ow resistance as refl ected in Manning's n or Darcy-Weisbach friction factor (ff) that are much higher than values for channel reaches with gradient <1% (Jarrett, 1984;Bathurst, 1985Bathurst, , 1993.…”

“…These objectives can be separated into two hypotheses: (i) there is a signifi cant difference between hydraulic geometry exponents for cascade versus step-pool reaches; and (ii) the variability in the hydraulic geometry exponents are signifi cantly related to the following potential control variables: bed gradient, channel roughness, wood load, and pool volume. The AHG for the single plane-bed reach is used for comparison with data collected from plane-bed reaches in British Columbia (Reid, 2005;Reid and Hickin, 2008). …”