USSES - an urban stream stability expert system

Charles D. Morris; Cesar Mendoza; Philip Thiem

An expert system for analyzing urban stream stability and developing mitigation measures for stream instabilities is developed using principles of the geomorphologic, hydraulic, and hydrologic processes that occur in a stream system and their effects on the system upstream and downstream. The hydrologic and hydraulic aspects of the system that affect flow in the stream and often the sediment load that enters the system from beyond the channel boundaries, as well as those aspects that are important to erosion processes are included in the expert system. Finally, available engineering knowledge of sediment transport and its importance to prediction of erosion and stream stability along with mitigation techniques used to restore stability are functionally included in this expert system. The first step is to determine which of the major processes are most important in a particular stream or reach of stream. These processes may include deposition, erosion, bed degradation, and lateral migration of the channel. This requires the stream to be investigated. By observing the stream as it is currently, by obtaining information on the urban development and the hydrologic impact of that development, within the basin (when and where), and determining changes in stream geomorphologic factors such as channel width/depth, channel meandering, effective discharge, or sediment load over time stream stability can be determined. To be able to fully comprehend all of the implications of this information and find an appropriate solution to problems that are discovered, it is necessary to have knowledge of stream geomorphology, urban surface water hydrology, and engineering mitigation techniques. Stream geomorphology is the study of the processes that are causing changes in the physical system and their effects on the system must be understood. The aspects of surface water hydrology important in this instance deal with the processes that affect flow in the stream and the sediment load that enters the system from beyond the channel system. Finally, knowledge of how and when available mitigation techniques can be applied to induce stability in a stream are essential components of the expert system. In order to effectively address the problem it is necessary to look at all aspects of the streams where problems are occurring. While it might alleviate the symptoms to rip-rap or concrete-line a bank area where excessive erosion is occurring, this will not solve the problem, as the sediment capacity of the stream is not changed. Instead, a new area of erosion will occur to supply the stream with its required sediment load. A better approach is one that takes into account the stream processes and addresses the causes of the problems, rather than simply treating the effects. Optimal solutions that are cost-effective and more natural in appearance may be well suited to some of the situations, and the number of occasions when more drastic means of solving sediment control problems need to be instigated can be reduced. By applying geomorphologically sound, engineering approaches to the problems of erosion control in an urban environment, many aspects of the problem can be considered to provide a solution that is beneficial environmentally, hydrologically, and economically. Through the use of sediment models along with hydrologic and hydraulic models, properly engineered solutions can be developed. By determining the required information to perform such an analysis and using efficient methods of collecting the information, an effective plan could easily be implemented by an urban community. The Urban Stream Stability Expert System, USSES may avert many future problems. In residential areas within a city where there are problems, mitigation measures that save property values by protecting property from degradation by using an aesthetically pleasing technology can be extremely valuable. Further, this system's value increases when actions taken in a specific area also serve to mitigate future, downstream problems. The ability to distinguish future problem areas is also a valuable one. If this type of procedure can be easily applied by a city, then it is possible to reduce problems by applying proper strategies to developing areas as they develop.

USSES - an urban stream stability expert system

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USSES - an urban stream stability expert system

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