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VI-7 point sources. During the April through September 1980, point sources accounted for only about 14 percent of the flow yet produced about 67 per- cent of the phosphorus and nitrogen loads an& about 24 percent of the total organic carbon load from all sources(3). bilization will consist of riprap beneath the normal water surface and r'ip- rap mixed with earth above the normal water surface. Revegetation will occur in the earth which wi 11 be mixed in with the riprap above the normal water surface. At crossings between meanders, cobbles will be placed on the river bottom to stabilize bottom sediments. Sank stabilization with riprap and bottom stabilization with cobbles will be carrieD out only in selected locations, and in both cases, only minimal excavation will be required. Stormwater runoff loads were significant for total suspended solids and total lead. The relative percentages of volume produced from stormwater were, however, small in comparison with other sources. Data presented in Table VI-II indicate that stonn runoff was only 9 percent of the volume of water that passed through the basin between April and September 1981, yet stormwater contributed about 76 percent of the total suspended solids load. A similar pattern is evident for lead where 47 percent of the total basin load was due to stormwater runoff. In comparison, only about 5 percent of the nitrogen and phosphorous loads was carried by the storm runoff volume in the basin. Incorporating riprap into stream banks and zones of cobbles in selected reaches of the river bottom will limit erosion within the river channel, and will provide aquatic habitat which has not previously existed in the river in Adams County. Cobbles and riprap should be incorporated in such a way that they will not be buried by sediment and not subject to being washed downstream. Other artificial habitat improvement structures should be investigated. As the result of the introduction of large riprap and smaller cobbles, variable velocities will be associated with the channel; such variability is important ecologically. IMPACT DF FLOOD CONTROL ALTERNATIVES ON RIVER WATER WUALITY Introduction The following discussion represents a brief synopsis of the implications of stream-bank stabilization, 1 imited channelization and potential lake devel- opment. This discussion is general in nature rather than site specific. A detailed water quality analysis of the South Platte River, both under exist- ing conditions and under conditions associated with future modifications, is beyond the scope of this report. Although vegetation which currently exists along the shoreline will tempor- arily be destroyed during the placement of riprap, sucn vegetation will quickly be reestablished; therefore, sediment will be secured a9ainst ero- sion and particular types of vegetation, which can serve as either nutrient sources or sinks depending upon ambient nutrient concentrations in the river, will be restored. Implications of Streambank Stabilization and Limited Channelization Generally, the activities of streambank stabilization and limited channeli- zation as described within this Master Plan will not permanently adversely affect water quality and the aquatic habitat of the South Platte River. To the contrary, the stabilization and channelization proposed may be benefi- cial to the aquatic habitat of the river. In the aftermath of construction activity in the river, flows may contain enough sediment to give the water a cloudy appearance and limit light trans- missibility. High turbidity levels will adversely affect aquatic habitat in various ways, although these effects will only be temporary in nature. Streambank stabilization will focus on outside bends of the river at selec- ted locations, while inside bends will be left as they are presently. Sta- The interaction between flowing water and bottom sediments is important in a river. Sediments can alternately retain nutrients, metals and other sub- stances or export these substances depending upon various environmental fac- tors. The capability of bottom sediments to export or retain substances is