Geoscience Reference
In-Depth Information
near gauge stations or control structures where measured flow and sediment data are
available for determination of boundary conditions.
Computational grid
The study channel is represented by a suitable number of cross-sections. Each pair
of consecutive cross-sections defines a reach between them. For a channel network,
the cross-sections at channel confluences, splits, and hydraulic structures should be
arranged according to the requirements of the used model.
Channel topography
Each cross-section is represented by finite points (stations), as shown in Figs. 5.3 and
5.4. The bed elevations and the distances to the left bank at all points should be
measured. The reach lengths between cross-sections are also needed.
If hydraulic structures are involved, their geometries and hydraulic conditions
should be provided.
Manning roughness coefficient
TheManning n is usually estimated using measured flow data. Empirical formulas may
be used if no measurement data are available. The n values in streams with similar
flow and sediment conditions may be used as reference.
Sediment particle properties
The specific gravity and shape factor of sediment particles should be measured. For
most natural sands (quartz sands), the specific gravity is about 2.65, and the Corey
shape factor is about 0.7.
The sediment size range should cover all sizes of bed load, suspended load, bed
material, and bank material existing in the study domain. Wash load is sometimes
also included. The entire size range is divided into a suitable number of size classes.
The representative diameters and upper and lower bounds for all size classes should
be determined.
Bed-material size and gradation
The initial bed-material gradation must be given for a realistic computation of stream
behavior, particularly for determining scour and stability conditions. If only deposition
is expected, such as sedimentation in reservoirs, the initial bed-material gradation is
less important.
The bed-material porosity is also needed.
Bank-material properties
If bank erosion and mass failure are considered, bank-material properties, such as
density and size composition, should be determined. For a cohesive bank, the cohesion
and friction angle of the bank material, as well as the critical shear stress for bank toe
erosion, are also needed.
Search WWH ::




Custom Search