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<br />e <br /> <br />e <br /> <br />e <br /> <br />DRAINAGE CRITERIA MANUAL (V. 2) <br /> <br />HYDRAULIC STRUCTURES <br /> <br /> <br />Photograph HS-10 <br /> <br />Boatable channels of the District waterways provide enjoyment to a wide variety of citizens. <br />This South Platte River channel provides an easily accessible boating experience. <br /> <br />2.8 Construction Concerns: Grass-Lined Channels <br /> <br />The selection of a drop or a grade control check and its foundation may be tempered by construction <br />difficulty, access, material delivery, etc. Some of the important concerns are discussed below, although <br />this is by no means an exhaustive list of the concerns possible for every site and situation. <br /> <br />2.8.1 Foundatjon/SeeDaae Control. Initial items that are especially important are site water control and <br />foundation conditions. A common problem is destabiiization of the foundation soiis by rapid local <br />dewatering of fine-grained, low-permeability soils, rather than continuous pumping rates at perimeter <br />locations that allow the entire construction area to remain stable. Water control during construction of a <br />drop structure is an essential precaution to present to a contractor. Diversion berms should be designed <br />with planned berm failure points to avoid flooding of drop-structure sites during construction. <br /> <br />The actual subgrade condition with respect to seepage controi assumptions must be inspected and field <br />verified. The engineer who established the design assumptions and calculated the required cutoffs <br />should inspect the cutoff for each drop and adjust the cutoff for the actual conditions encountered. For <br />example, if the inspection of a cutoff trench reveals a sandy substrate rather than clay, then the cutoff <br /> <br />06/2001 <br />Urban Drainage & Flood Control District <br /> <br />HS-37 <br />