FLOOD03929

• County: Statewide
• Community: Nationwide
• Basin: Statewide
• Title: Generalized Computer Program Fluvial-12 Mathematical Model for Erodible Channels Users Manual
• Date: 8/1/1986
• Prepared By: Howard H. Chang, Ph.D., P.E.
• Floodplain - Doc Type: Educational/Technical/Reference Information

q; = tan ~q,.. ... ... ...... .. ... ... ... '" ... .. . .... .. . .., . ... . .., (6)

in which q; = transverse sediment rate per unit channel length; and q,
= longitudinal sediment rate per unit width. Erosion of the concave bank
is simulated by the removal of sediment and bank collapse due to the
combined effects of velocity and gravitational force. Because bank sta-
bility depends on a large number of factors including bank height, slope
angle, drainage state, cohesion, etc. (17), the rate of bank erosion given
by Eq. 6 is multiplied by a coefficient of bank erosion which is deter-
mined based upon river data. The change in channel-bed elevation at a
point along a section is obtained from the continuity for sediment in the
transverse direction, or

az 1 a
(1 - ).) - + - - (rq;) = 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. (7)
at r ar
in which z = channel-bed elevation at a point; and r = radial or trans-
verse coordinate. With a forward difference in r for the spatial derivative
as suggested by Chang and Hill (3), the change in channel-bed elevation
.u for a time step ilt due to transverse sediment movement is

At 2 rk+lq~+l - Tkq;t
ilz, = ........ "..................... (8)
1 - ^ Tic + TIc+1 '.1:+1 - Tic

in which k = radial coordinate index counted from the convex bank to-
ward the concave bank.

MooIl. DacIuPnoN

The mathematical model FLUVIAL-ll has been developed; its input
data, computing procedures and output parameters are described.
Input Data.-Input to the model include the initial cross sections,
channel roughness, initial bed-material composition, inflow hydrograph
and physical constraints such as check dams, rigid banks, bedrock out-
crops, etc. The input data follow the HEC-2 (9) format.
Computing Procedures.-Major steps of computation in the model in-
clude the following:

1. Enter input data.
2. Compute water-surface elevations and sediment loads at all cross
sections.
3. Set t = t + ilt,
4. Determine changes in channel cross-sectional area using techniques
for sediment routing.
5. Compute and apply changes in channel width.
6. Obtain new channel-bed profiles. .
7. Compute and make changes in cross-sectional profile due to lateral
migration for those sections in channel bends.
8. Update bed-material compositions.

Mer step 8, the computation returns to Step 2 for another time step.
The !te.ration continues until the required time period is covered.

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