Geoscience Reference
In-Depth Information
impingement at the downstream of sluice gates, spillways, and overfalls. Local erosion
is the major reason for the failures of many structures. Because of the complexity of the
processes involved, the prediction and prevention of local erosion around structures
are very challenging.
Sediment problems in estuaries
Morphodynamic processes under the actions of river runoff, tidal flow, and wave
currents in estuaries are extremely complex. A large amount of fine-grained cohesive
sediments coming from rivers are deposited in estuarine regions, forming mouth bars
and reducing the flow depth in navigation channels. Salinity intrusion intensifies the
deposition of cohesive sediments and affects the water quality. Fine-grained sediments
also enter harbors and cause significant deposition there. Training works and dredging
are necessary to maintain the navigation channels.
Watershed management
Water bodies, such as rivers, lakes, and reservoirs, receive water runoff and sediment
load from uplands. Serious erosion in the uplands increases the downstream sediment
load, causing sedimentation and reducing the storage and transport capacities of down-
stream river systems. Conversely, a reduction in the erosion of uplands decreases the
downstream sediment supply, causing channel degradation, headcutting, and bank
instability. Rational watershed management is essential for both uplands and river
systems.
Sediment-related environmental problems
Environmental quality is an important global issue. Wastes from industry and agricul-
ture impair not only the water quality, but also the sediment quality in the receiving
river systems. Sediments, especially clay and silt, are associated with the transport of
many pollutants. The impaired sediments also accumulate on the channel bed with
time, and later become a major source of pollution through resuspension.
1.2 ROLE OF COMPUTATIONAL SIMULATION
IN RIVER ENGINEERING ANALYSIS
River flow and sediment transport are among the most complex and least understood
processes or phenomena in nature. It is very difficult to find analytical solutions for
most problems in river engineering, and it is very tedious to obtain numerical solutions
without the help of high-speed computers. Therefore, before the 1970s, many river
engineering problems had to be solved through field investigations and laboratory
physical models (also called scale models). With the recent advancements in computer
technology, computational models have been greatly improved and widely applied to
solve real-life problems. One-dimensional (1-D) models have been used in short- and
long-term simulations of flow and sediment transport processes in rivers, reservoirs,
and estuaries. Two-dimensional (2-D) and three-dimensional (3-D) models have been
used to predict in more detail the morphodynamic processes under complex flow
