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I . • I Maintenance. Control structures and catch basins have a history of maintenance-related problems and it is imperative that a good maintenance program be established for their proper functioning. A typical problem is that sediment builds up inside the structure which blocks or restricts flow to the inlet. To prevent this.probleln these structures should be routinely cleaned out at Ieast twice per year. Regular inspections of control structures should be conducted to detect the need for . non-routine cleanout,especially if construction or land-disturbing activities are occurring in the contributing drainage area. I • A 15-foot wide access road to the control structure should be installed for • inspection and maintenance. ITable 3.5 provides maintenance recommendations for control structures and catch basins. I Table 3.5 Maintenance of Control Structures and Catchbasins • Maintenance Results Expected When I Component Defect Condition When Maintenance is Needed Maintenance is Performed • General mash and Material exceeds 25%of sump depth or 1 foot Control structure orifice is not • Debris below orifice plate. blocked. All trash and debris (Includes removed. Sediment) Structural Structure is not securely attached to manhole Structure securely attached to wall . Damage wall. and outlet pipe. I Structure is not in upright position(allow up to Structure in correct position. 10%from plumb). ' 'Connections to outlet pipe are not watertight and Connections to outlet pipe are water show signs of rust. tight;structure repaired or replacedI and works as designed. Any holes—other than designed holes--ia the Structure hue no holes other than structure. designed holes. I Gate ut Damaged or Cleanont gate is not watertight or is missing. Gate is watertight and works as Gate Missing . designed. • Gate cannot be moved up and down by one Gate moves up and down easily and is . maintenance person. watertight. I Chain/rod leading to gate is missing or damaged. Chain is in place and works as. designed. Gate is rusted over 50%of its surface area- Gate is repaired or replaced to meet design standards. Orifice Plate Damaged or Control device is not working properly due to Plate is in place and works as Missing missing,out of place,or bent orifice plate. designed. Obstructions Any trash,debris,sediment,or vegetation Plate is free of all obstructions and blocking the plate. works as designed. Overflow Obstructions Any trash or debris blocking(or having the Pipe is free of all obstructions and Pipe potential of blocking)the overflow pipe. works as designed. IFebruary 2005 . Volume Ill—Hydrologic Analysis and Row Control BMPs . 3-55