Storm Drainage Standard - Laserfiche WebLink

Home

b. Minimum pipe cover in easement areas without vehicular traffic shall be 1'_0,1. c. Maximum permissible depth will be deter- mined from current loading tables in pipe handbooks for the respective pipes, using 110 lbs. per cu. ft. as the weight of earth. d. All pipes shall be installed using a first class bedding trench condition. Proper foundations shall be provided for pipes. Pipes on unstable ground or fresh fill shall be supported by a method acceptable to the Chief Engineer. e. Drain pipes installed along the longitu- dinal axis of the roadway shall be located in the pavement area between curbs. 1. Other Closed Conduits. There shall be no minimum cover or maximum permissible depth requirements for closed conduits other than pipes except that such structures shall be designed to support all loads that it shall be subjected to. O MANHOLES AND INLETS 1. Manholes: a. Location. Manholes shall be located at all changes in pipe size and changes in alignment or grade and at all junction points. b. Spacing. Maximum manhole spacing shall be 250 feet for pipes 36 inches or less in diameter, or box drains with the smallest dimension less than 36 inches. Maximum manhole spacing for larger pipes and box drains shall be 500 feet. c. Special Details. Bottoms of manholes and inlets serving as manholes shall be shaped to channelize flow and sloped with slope of pipe as shown in "Design Details." 2. Inlets (Catch Basins) a. Location. Inlets shall be located at the upstream side of intersections, in sumps and where required by quantity of flow. b. Spacing. Maximum spacing shall be 500 feet. c. Types. For gutter grades up to 4 %, stand- ard 10 -foot curb inlets with a depressed gutter shall be used. For grades 4% and greater, 10 -foot long deflector inlets shall be used. d. Capacity. Inlet capacities as follows are acceptable: 8 Type Gutter Grade cfs (1) Std. depressed 0.4% 6 gutter inlet 4.0% 4 sump 10 (2) Deflector Inlet 4.0% 4.5 12.0% 5.5 Greater than 12.0% 6 max. e. Gutter Flow. The gutter flow shall not exceed a width of 8 feet. ® PIPE SYSTEM ANALYSIS Generally speaking, the pipe system shall be analyzed by sections, that is, outlet to manhole, manhole to manhole or manhole to inlet. The analysis shall start at the lowest point of flow and continued upstream. The design flow shall be used in determining whether the pipe will flow full or partially full. Full consid- eration of- the tailwater, entrance and critical flow conditions shall be made. 1. Pipe Flowing Full. If the conditions show that the pipe section will flow full, the prin- ciples of flow of water in closed conduits shallbe use . The water surface elevation of the upstream manhole is determined by adding the pipe friction and manhole losses to the water surface elevation of the down- stream manhole or the beginning elevation as previously stated. 2. Pipe Flowing Partially Full. If the condi- tions show that the pipe section will flow partially -full, the principles of flow of water in open channels shall be used. The pipe partially -full condition maybe determined from the Pipe Flow Charts on pages 23 to 31. The tailwater condition must also be considered in this determination. 3. Manhole Losses a. For junction conditions such as drop man- holes, or where the outflow line deflects more than 10° with any inflow line, the hydraulic grade shall be- determined by applying the Entrance Control loss and C & D losses (where applicable), or A, B, C & D losses, whichever is greater. b. For junction conditions where the outflow line deflects 100 or less with the inflow line, the hydraulic grade shall be deter- mined by applying the A, B, C & D losses. © HYDRAULIC GRADIENT COMPUTATIONS The hydraulic gradient is (1) a line connecting points to which water will rise in manholes and inlets through- out the system during the design flow or (2) the level of flowing water at any point along an open channel.