Lower Arkansas Districts 10_14_17&67 Diversion Inventory

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September 15, 2004 Lower Arkansas River Basin Districts 10, 14, 17 and 67 Diversion Structure Inventory flow through the structures made a thorough inspection of the dam/spillway basin or diversion structure concrete apron (floor) difficult or impossible" The components of the structures that are normally submerged should be made visible for a complete and accurate evaluation. 4.0 CONCEPTUAL REPAIR PLAN The basic features, visible damage and a conceptual repair plan are described in a short narrative for each structure, which can be found in Appendices B, C, D and E. Crack Repair - There were different types of cracks encountered at most of the structures. Hairline cracks are commonly found in concrete, usually do not affect the integrity of the structure, and do not generally require repair work" Cracks that are between approximately X-inch and %-inch in width are more serious, and will usually require repair. Oftentimes injecting a pressurized grout into such a crack will help preserve the structure's integrity. Depending upon the location of the crack within the structure, bridging across the crack with a series of straps fastened to the concrete surface is another option to slow any movement of the structure" Cracks that are larger than approximately ~-inch in width or structures with differential settlement or movement between two adjoining sections of concrete would normally require complete or partial replacement rather than repair. Such replacement should include doweling steel reinforcement into the existing portion of concrete, and prior to placement of the new section of concrete, connecting the dowels to the steel reinforcement placed within the new section. Stabilization - River bottom, Channel bottom and bank stabilization is typically recommended in locations where the hard surface (concrete) of a structure ends and soil begins. However, the need for stabilization will ultimately depend on the type of soil and velocity of flow through the structure. Sandy soil, for example, is extremely erosive, but sandy soil exposed to low velocities of flow may not be. The potential damage to downstream soil caused by flow through the structure will also depend on the setting or orientation of the gates. Since the gates are frequently adjusted, the velocity of flow is frequently changing and the resulting damage is unpredictable. If not already present, installation of stabilization at the locations mentioned above is therefore recommended in almost all cases. It is recommended that the material used for stabilization be angular-shaped rock (riprap) or grouted boulders. The designer will determine the layer thickness of riprap or size of boulders, which will depend on the anticipated flow conditions, including: velocity, how flow is directed, danger of undermining the basic structure, etc. It may not be feasible to use riprap or boulders in some cases, or access to/availability of a quarry may be limited. In such cases concrete rubble could be used, as long as it is of the same approximate design size and layer thickness as the riprap or boulders. Trash Rack - A trash rack typically consists of a structural steel framework installed immediately upstream of the diversion structure. Water is allowed to pass through it, and the framework is designed to help collect debris conveyed by the river before it reaches the structure. Otherwise, the debris could build up at the structure's headwall and potentially interfere with the operation of the gates. A trash rack was recommended for almost every diversion structure. However, the need for a trash rack will ultimately depend on the actual amount of debris encountered on a long- Farnsworth Group Page 3