Model help:DredgeSlotBW: Difference between revisions
No edit summary |
No edit summary |
||
Line 84: | Line 84: | ||
| D<sub>50</sub> | | D<sub>50</sub> | ||
| median grain size (sand) | | median grain size (sand) | ||
| | | mm | ||
|- | |- | ||
| D<sub>90</sub> | | D<sub>90</sub> | ||
| grain size such that 90% is finer (sand) | | grain size such that 90% is finer (sand) | ||
| | | mm | ||
|- | |- | ||
| R | | R |
Revision as of 18:12, 13 April 2011
DredgeSlotBW
This model is a calculator for aggradation and degradation of sediment mixtures in gravel-bed streams subject to cyclic hydrographs.
Model introduction
This program calculates the 1D bed evolution of a sand-bed river after installation of a dredge slot. The calculation begins with the assumption of a prevailing mobile-bed normal flow equilibrium before installation of the dredge slot. The flow depth H, volume bedload transport rate per unit width q_{b} and volume suspended transport rate per unit width q_{s} at normal flow are computed based on input values of discharge Q_{ww}, channel width B, bed material sizes D_{50} and D_{90}, sediment submerged specific gravity R_{r} and bed slope S.
The sediment is assumed to be sufficiently uniform so that D_{50} and D_{90} are unchanging in space and time. The input parameter Inter specifies the fraction of any year for which flood flow prevails. At other times of the year the river is assumed to be morphologically dormant.
The reach is assumed to have length L. The dredge slot is excavated at time t = 0, and then allowed to fill in time with no subsequent excavation. The depth of initial excavation below the bottom of the bed prevailing at normal equilibrium is an input variable with the name Hslot. The dredge slot extends from an upstream point equal to r_{u*L} to a downstream point rd*Hslot, where ru and rd are user-input values.
The porosity lamp of the sediment deposit is a user-input parameter.
The bedload transport relation used in the calculation is that of Ashida and Michiue (1972). The formulation for entrainment of sediment into suspension is that of Wright and Parker (2004). The formulation for flow resistance is that of Wright and Parker (2004). The flow stratification correction of Wright-Parker is not implemented here for simplicity. A quasi-equilibrium formulation is used to computed the transport rate of suspended sediment from the entrainment rate.
A backwater calculation is used to compute the flow. The water surface elevation at the downstream end of the reach is held constant at the value associated with normal flow equilibrium.
Iteration is required to compute: a) the flow depth prevailing at normal flow; b) the friction slope and depth prevailing at normal flow, b) the friction slope and depth associated with skin friction associated with skin friction from any given value of depth, and b) the minimum Shields number below which form drag is taken to vanish.
Model parameters
Uses ports
This will be something that the CSDMS facility will add
Provides ports
This will be something that the CSDMS facility will add
Main equations
A list of the key equations. HTML format is supported; latex format will be supported in the future
Symbol | Description | Unit |
---|---|---|
Q_{w} | flow discharge | m^{3} / s |
I_{f} | flood intermittency | - |
B | channel width | m |
D_{50} | median grain size (sand) | mm |
D_{90} | grain size such that 90% is finer (sand) | mm |
R | submerged specific gravity of sediment | - |
S | bed slope | - |
L | Reach length | m |
H_{slot} | depth of dredge slot | m |
r_{u} | fraction of reach length defining upstream end of dredge slot | cm / s |
r_{d} | fraction of reach length defining downstream end of dredge slot | |
λ_{p} | bed porosity | - |
M | number of intervals | - |
∆_{x} | spatial step length | m |
∆_{t} | time step | year |
Mtoprint | number of time steps to printout | - |
Mprint | number of printouts | - |
a_{u} | upwinding coefficient: a_{u} = 1 corresponds to full upwinding | - |
Notes
In the calculation of River Bed Elevation Variation with a Dredge Slot: the river is assumed to be sand-bed. The calculation proceeds using a backwater formulation. Flow resistance is computed using the Wright-Parker (2004) formulation. The bedload transport rate is computed using the Ashida-Michiue (1972) formulation. The rate of entrainment into suspension is computed using the Wright-Parker formulation without the stratification correction.
Examples
An example run with input parameters, BLD files, as well as a figure / movie of the output
Follow the next steps to include images / movies of simulations:
- Upload file: http://csdms.colorado.edu/wiki/Special:Upload
- Create link to the file on your page: [[Image:<file name>]].
See also: Help:Images or Help:Movies
Developer(s)
References
Key papers