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- Info
Hydrologic information and analyses required for mitigating hydrologic effects of urbanization
| Author: |
Burges, Stephen J.; Stoker, Bruce A.; Wigmosta, Mark S.; Moeller, Rodney A. |
| Date: |
1989 |
| Periodical: |
Seattle, WA: University of Washington, Department of Civil Engineering, Environmental Engineering and Science; Water Resources Series Technical Report No. 117 |
| Abstract: |
The objectives were to characterize for gauged and ungauged catchments the pre-development hydrology and to determine or estimate the post-development hydrology and develop criteria for runoff control measures to mitigate hydrologic effects of development. Field observations combined with map and stereo aerial photograph interpretation are used to identify catchment features associated with runoff production. From these features the spatial distribution of dominant basin hydrologic processes is estimated. Hydrologic and geomorphic processes, not considered in traditional methods, that are identified by the process zone mapping procedure developed include areas of saturated overland flow, return flow, areas with significant water detention, and channel segments where sediment transport thresholds are likely to be exceeded. An overlay map of the- extent, location, and types of hydrologic process zones is prepared based on interpretation of the field data, aerial photographs, and map information. A similar process zone map is prepared for any proposed development configuration and differences between it and the pre-development conditions are summarized in tables, charts, and maps. Changes in drainage density, water detention volume, and quick storm response areas are associated with their respective downstream channels. Potential impact zones are defined by comparison of the pre- and postdevelopment runoff and channel conditions. Examination of the channel sections bars, and substrate for channel segments draining relatively undisturbed and changed parts of the catchment, respectively, indicate critical channel erosion problems and erosion and deposition potential. These locations dictate the extent of mitigative measures needed upstream; flow released from mitigative schemes must be constrained above the start of first order-channels if channel geometry and stream habitat are to be preserved. The method yields primarily two-dimensional zone maps and channel segments, each having several associated attributes. For file and data keeping purposes the information is stored most conveniently using an appropriate geographic information system (GIS). A relatively simple spatially-distributed rainfall-runoff model for quantitative decision making was developed using the mapped extent of flow production zones as subareas within subcatchments. Upper soil (and litter) and lower soil depths (attributes determined by direct field measurement) are included explicitly. This type of model shows promise as an important tool for demonstrating relative impacts of land use change at different locations within a subcatchment. The hydrographs determined for subareas provide guidance for the type and location of appropriate mitigative measures to reduce hydrologic impacts from land use change and urbanization in particular. The model needs further refinement and testing before its general applicability can be determined. |
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