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I I I I I I I I I I I I I I I I I I I Lower Big Dry Creek Hydrologic Study risk exists, regardless of the type of development and stormwater management implemented upstream. 3. Stream stabilization options for properties in the lower watershed consist of three primary steps: 1) reducing the slope of (i.e., laying back) steep cut banks, 2) providing armoring or other stabilization for these banks, particularly for the toe of the bank, and 3) revegetating the banks to help them resist future erosion. Specific techniques have previously been provided in BDCW A-sponsored reports and remain valid, as do the many techniques described by the NRCS. Given the relatively flat slopes in the study area, preliminary analysis suggests that, in general, grade control structures do not appear to be needed to stabilize the stream channel in this area; however, more detailed channel analysis would be needed to confirm this. 4. While concrete chunks placed along the bank to stabilize the stream may provide short- term benefits as a "stop-gap" measure under certain conditions, typically, placement does not adequately protect the toe (lower part) of the bank, so undercutting is likely to continue to occur, with the concrete eventually falling into the creek. Additionally, placement of concrete on one portion of the bank may cause impacts on another part of the bank, which should be taken into consideration. To comply with federal law, landowners should be sure to obtain a permit from,the U.S. Army Corps of Engineers to place concrete or other material along the streambank. From an engineering perspective, WWE strongly recommends against use of broken concrete to stabilize banks. 5. Planned detention in the urbanizing portion of the watershed should be aggressively pursued as a high priority. This is particularly critical in areas that currently provide inadvertent detention that has not been formalized by a legal agreement. Areas at particular risk include inadvertent detention sites on tributaries to Big Dry Creek along the 1-25 corridor where land prices are at a premium and rapid development is occurring. Additionally, the inadvertent detention at the railroad embankment on Colorado Blvd. is providing significant benefits to the downstream Weld County landowners. Opportunities to formalize and improve this detention area in a manner that help reduce flooding impacts to upstream Adams County landowners should be pursued. 971-179.092 June 2005 Page 7 Wright Water Engineers, Inc.