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<br />FLOOD CONTROL
<br />
<br />viding photo documentation of the
<br />study area,
<br />The hydrology and hydraulics used
<br />for this study were previously completed
<br />for the 1982 Master Drainageway Plan,
<br />Use of existing data can substantially
<br />reduce costs. Frequently, there are exist-
<br />ing flood studies that can be utilized to
<br />
<br />obtain much of the baseline hydrology
<br />and hydraulics needed for a stability
<br />study, For example, the Federal
<br />Emergency Management Agency main-
<br />tains the base infonnation and models
<br />for the Flood Insurance Studies (FIS) and
<br />Flood Insurance Rate Maps (FIRM), In
<br />addition, many communities are con-
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<br />Materials International, Inc.
<br />4501 Circle 75 Parkway Suite E.5370 Atlanta, GA 30339
<br />Phone 17701933.81660,18001256.8857 in the USA
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<br />For More Information, Circle #31
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<br />34oMarch/ApriI1996
<br />
<br />Land and Warer
<br />
<br />ducting Master Planning studies for
<br />basins which require the same hydrolog-
<br />ic and hydraulic infonnation,
<br />The hydrology infonnation used for
<br />the stability study included development
<br />of a Stormwater Management Model
<br />(SWMM) for both existing and fully
<br />developed conditions with the Fossil
<br />Creek watershed, Peak discharges for
<br />the 2-, 5-, 10-, 50-, 100-, and 500-year
<br />return period event were developed,
<br />The hydraulic analysis was done
<br />using the U.S, Army Corps of Engineers
<br />model HEC-2, Although the model was
<br />originally done for the 1982 Master Plan,
<br />the model had to be revised, Cross-sec-
<br />tions were field surveyed to include pre-
<br />sent channel conditions for the stability
<br />analysis, Accurate representation of the
<br />channel geometry is an imponant com-
<br />ponent for stability analysis,
<br />The HEC-2 analysis was used to
<br />generate the hydraulic parameters, such
<br />as velocity, hydraulic depth, and effec-
<br />tive flow width, which influence sedi-
<br />ment'transport characteristics for the
<br />peak discharges, Results of the
<br />hydraulic analysis were used to generate
<br />both bed material transport relationships
<br />and the bed material rating curves and
<br />sediment continuity analysis,
<br />Channel stability analysis generally
<br />includes three levels of analysis; 1)
<br />Qualitative, involving geomorphic con-
<br />cepts; 2) Quantitative, involving geo-
<br />morphic concepts and basic engineering
<br />relationships; and 3) Quantitative involv-
<br />ing sophisticated mathematical models,
<br />For the study of Fossil Creek, only Level
<br />1 and II analyses were completed, The
<br />results of the analysis provided a basis
<br />for; 1) the determination of both short-
<br />and long-term trends of the Fossil Creek
<br />channel, 2) establishment of erosion
<br />buffer limits for current and future devel-
<br />opment, and 3) engineering design of
<br />channel stabilization measures,
<br />The qualitative geomorphic analysis
<br />(Level I) is based on a field reconnais-
<br />sance, aerial photos, and mapping, and
<br />relies strongly on expertise and practical
<br />experience, Qualitative geomorphic
<br />techniques are based on an understand-
<br />ing of the physical processes governing
<br />watershed and river response. Level I
<br />analysis attempts to predict watershed
<br />and stream response with only a general
<br />
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