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<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 />I <br />I <br />I <br />I <br />I <br /> <br />Lower Big Dry Creek Hydrologic Study <br /> <br />. Analysis of thE: adequacy of existing and proposed stormwater detention in the urban <br />portion of the watershed based on review of master drainage plans and comparison to <br />estimated requirements using engineering "rules of thumb." <br /> <br />. Conceptual-level characterization of expected future hydrologic conditions. <br /> <br />. Identification and conceptual recommendations regarding strategies to address drainage <br />and flooding problems, including detention/storage, channel stabilization, targeted <br />infrastructure improvements, policies and planning strategies, acquisition of floodprone <br />land, public education regarding flood protection and public education regarding land <br />management strategies to reduce susceptibility to erosion. <br /> <br />Findings of Hydrolo1gic Analysis <br /> <br />1. Many factors influence the character of Big Dry Creek in Adams and Weld Counties. <br />Key factors include: naturally occurring erosion-prone soils and stream characteristics; <br />urbanization in the central portion of the watershed resulting in wastewater and <br />stormwater discharges to the creek that did not occur historically or have increased; <br />increased base flows related to urbanization; releases from Standley Lake; irrigation <br />diversions and return flows; stream crossing structures; and land management practices in <br />the lower watershed that decrease vegetative cover along the streambank. While this <br />report does not assign relative responsibility of these factors to conditions present in Big <br />Dry Creek, it does describe each of these factors in more detail, particularly stormwater <br />management strategies in the urbanized portion ofthe watershed. <br /> <br />2. The character of Big Dry Creek in Adams and Weld Counties is consistent with a plains <br />stream type description that includes shifting channels, eroding banks and bar migration. <br />This type of stream is described as being transient, with little structural stability. Big Dry <br />Creek exhibits these characteristics, indicating a naturally occurring pre-disposition to <br />eroSIOn. <br /> <br />3. The "flashy", variable flows that occur in the watershed in response to storm events cause <br />increased bank erosion by preventing the stream from reaching a state of equilibrium. <br /> <br />971-179.092 <br />June 2005 <br /> <br />Wright Water Engineers, Inc. <br /> <br />Page 3 <br />