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<br />- <br /> <br />II <br />II <br />II <br />~I <br />I <br />I <br />'I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />,I <br />I <br />,I <br />II <br />II <br /> <br />Lower Big Dry Creek Hydrologic Study <br /> <br />flow that lacks sediment (Knighton 1998). In order to balance the sediment <br />transport capacity of the high flow, sediment is removed from the banks of the <br />stream. This relationship is known as Lane's Balance. As sediment is removed <br />from the bank, surface erosion, undercutting and sloughing can occur. As the <br />flow recedes, the banks dry again, and the cycle repeats itself (Knighton 1998). <br />Thus, peak flows associated with a highly variable flow will be more erosive than <br />a peak flow associated with a consistent flow regime. The more flashy, or <br />variable, a flow is, the more destructive it is to the streambanks. Analysis of Big <br />Dry Creek flow data indicates that the flow regime has changed to become more <br />variable, and more likely to cause erosion. It also indicates that the flow in the <br />upper (more urbanized) portion of the watershed is more variable than the lower <br />portion (Gossenauer and Wachob 2001).1 <br /> <br />In addition to the studies described above, the Big Dry Creek Watershed Management Plan <br />provided these key recommendations and conclusions that relate to this project including: <br /> <br />. Hydrologic modification of the creek from increased stormwater flows related to <br />urbanization will require continued attention by local governments and the <br />Watershed Association. In both the urban and agricultural portions of the <br />watershed, specific areas have been identified that would benefit from stream <br />restoration activities. <br /> <br />. Local government enforcement of existing stormwater ordinances relating to <br />detention of storm water flows and erosion and sediment controls at construction <br />sites is critical to protecting Big Dry Creek water quality and habitat. In general, <br />the local governments are believed to have appropriate ordinances in place for <br />new development and redevelopment of existing areas. <br /> <br />. Storm water flows and pollutant contributions have not been well characterized <br />relative to the strong base of information associated with ambient stream <br />conditions. This is an area of additional study that the Watershed Association <br />may want to consider. <br /> <br />. Considerable data have been collected on erosion and sedimentation issues in the <br />agricultural portion of the watershed. Sufficient information is believed to have <br />been developed to support local landowners in obtaining grants to help stabilize <br />portions of the streambank. Based on information provided by the NRCS, it is <br />critical that the landowner initiates the grant application process. The Watershed <br />Association can provide the landowners with a good base of information to help <br />facilitate this process. <br /> <br />1 Since completion of the Gossenauer and Wachob (2001) study, issues regarding accuracy of the Fort Lupton gage <br />have been identified, which may mask actual changes in hydrology in the lower watershed. <br /> <br />971-179.092 <br />June 2005 <br /> <br />Wright Water Engineers, Inc. <br /> <br />Page 24 <br />