Figure 4.14. Colby's correction curves for temperature and fine sediment (Colby 1964).
2. Uncorrected sediment discharge qn for the given V, yo, and D50 can be found from
Figure 4.13 by first reading qn knowing V and D50 for two depths that bracket the
desired depth and then interpolating on a logarithmic graph of depth versus qn to get
the bed sediment discharge per unit width.
3. Two correction factors k1 and k2 shown in Figure 4.14 account for the effect of water
temperature and fine suspended sediment on the bed sediment discharge. If the bed
sediment size falls outside the 0.20 mm to 0.30 mm range, the factor k3 from Figure
4.14 is applied to correct for the effect of sediment size.
4. Unit bed sediment discharge qT corrected for the effect of water temperature,
presence of fine suspended sediment and sediment size is given by the equation
qT = [1 + (k 1k 2 - 1) k 3 ] qn
As Figure 4.14 shows, k1 = 1 when the temperature is 60F, k2 = 1 when the concentration of
fine sediment is negligible and k3 = 1 when D50 lies between 0.2 mm and 0.3 mm. The total
sand discharge is
Q T = Wq T
Width of the stream
Colby (1964) found that: "The agreement of computed and observed discharges of sands for
sediment stations whose records were not used to define the graphs seemed to be about as