Sediment routing in bedrock-controlled channels
Date
2007-03-01T11:57:53Z
Authors
Odiyo, John Ogony
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Abstract
A sediment budget model in which each steady discharge scours sediment along a
trajectory towards ultimate target storage or deposits sediment towards the same ultimate
target storage has been conceptualized and developed. The method is aimed at routing
sediment in morphologically diverse bedrock-controlled channels in which sediment
transport and storage is not a continuous process in space and time and mostly occurs in
response to discrete discharges. The relative value of the ultimate stable scour depth
(Huss) for each steady discharge with respect to the current scour depth after adding
sediment supply determines the potential to scour or store sediment.
Scour depths measured at discrete locations along the longitudinal profile of a laboratory
pool at discrete times until changes in scour were not discernible for each steady
discharge and sediment size have been integrated to provide the Huss and storage
depletion curve. The experimentally established dependence of scour depth on critical
flow depth, settling velocity and sediment supply formed the basis of generating
dimensionless Huss and storage depletion curve from these parameters using the
Buckingham π theorem. The optimization of experimental results to generate the storage
depletion curve gave the exponent of time (φ) and the exponential decay factor (k) as 0.5
and 0.0040207 respectively. Regression fit of dimensionless Huss and critical flow
intensity gave a linear relationship with a gradient of 0.90214, y-intercept of –1.4766 and
R2 of 96%.
The suitability of the model for budgeting sediment dynamics in a series of connected
storage units, the validity of using the relative values of Huss and the current scour depth
after adding sediment supply to determine scour potential and the existence of active
storage associated with sediment supply for each steady discharge have been confirmed
experimentally. Modelling with equivalent steady discharges computed from unit stream
power principles on the rising and the falling limbs of the hydrograph resulted in scour on
the rising limb of magnitude dependent on the magnitude and sequence of the flood
event, and less or no scour on recession. The modelling concepts and approach have thus been validated and the potential to reasonably simulate sediment storage changes in
bedrock-controlled rivers demonstrated.
Description
Student Number : 9700136A -
PhD thesis -
School of Civil and Environmental Engineering -
Faculty of Engineering and the Built Environment
Keywords
Bedrock-controlled channels, sediment routing, scour depth, active storage