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I I I I I I I I I I I I I I I I I I II at a rate \^ihich allows nature and the ecosystem to adjust to the changing land- scape. When activities of man are superimposed, the rate of erosion often increases beyond the ability of the ecosystem to adjust, thereby, resulting in adverse impacts on the envil'onment. The most salient concern is the impact upon water quality and the maintenance of a supply already appropriated. From water erosion impacts, con- sideration must be given to: ' -Hater erosion factors: Rainfall Soil s Slope gradient and length Vegetation -Acceptable level of risk -Erosion and sediment control plans: Implementation cost Temporary versus permanent Benefit/Cost measures ,later erosion control measures may include: -Soil stabilization methods -Runoff control -Structural control Soil stabilization often can be achieved from fast-growing annual and perennial grasses during the construction phase and prior to final grading and establishment of permanent vegetation, Other measures include mulches, nettings and chemical binders. Structural measures most often used are those which intercept surface runoff and convey it to a safe disposal area. Diversion structures include dikes, ditches, and terraces. Heasures as described above may be used to control water erosion of a tem- porary basis during construction. Sedimentation is the process by which suspended particles are removed from water. Such particles are carried in suspension by water and settle out only under certain conditions. Some clay particles are kept in suspension by electrical charges for in- definite periods. Erosion rates increase with increasing runoff flow quantity and velocity, Sedimentation could have a detrimental impact upon the quality of water within the Parkville Hater District. The construction of roads, installation of utilities and site grading may cause an increase in sedimentation. Sediment control measures may be employed to lessen the impact. Critical areas along streams should be delineated and control measures iden- tified and installed prior to site alteration, Sediment control measures may include the fo 11 owi nq: a. Filtering: Vegetative and b. Trapping: structural-buffers -contour strips -sod inlet filters -gravel inlet barriers -rock berms -straw bale sediment barriers Sediment traps and basins The potential negative impact upon the study area from erosion provides a basis for requiring a full assessment of the ip:pact prior to permitting development, An ero- sion assessment report should be prepared by a qualified soil engineer and should 9