Sewers flow capacity

Flow capacities, velocities and slopes (for sewers running 3/4 full) can be coordinated so that the curves shown on Figures 8-9 and 8-10 will give the size of the sewer line required for the assumed slope and velocity at the desired flow capacity in gallons per minute. 

Flow capacities, velocities and slopes of sewer lines should be contingent on the grades available at the plant site. The flat grades necessary at most plant sites will be a determining factor in the slope... 

Concrete, metal or plastic pipes are conventionally used in stormwater sewers for urban surface runoff drainage. A stormwater sewer pipeline is laid parallel to the ground surface with a cover of more than 0.9 m. Scrap tire pipes may be used as the construction material of storm drainage systems in small towns if the pipes can provide required flow capacity. 

Other applications include storm-sewer flow augmentation, where added polymers can temporarily increase the flow capacity of storm sewers in times of heavy rain, etc. Another application has been for fire fighting. Water flow rates can be increased, smaller hose lines used, and nozzle pressures raised by the addition of polymer. 

For example, doubling the flow capacity of the sewer would increase the cost by only 30 percent. 

There are several considerations that must be reviewed prior to the sliplining procedure. You will need to establish the minimum anticipated clearance that will exist between the lining material and the existing sewer pipe. Flow capacity is another factor to establish. Will there be external loads on the pipe What will the earth load be Is hydrostatic pressure expected Internal pressure and construction loads are additional considerations. How will structural support of the pipe be aeating with grouting ... 

Sufficient flow capacity for the anticipated hydrauhcs of a rehabilitated sewer system can be ensured by choosing the proper inside diameter for the pipe liner. Wall stiffness of a hner pipe must be adequate to withstand external pressure from such things as ground water. 

A concrete pipe storm sewer, 4 ft in diameter, drops 3 ft in elevation per mile of length. What is the maximum capacity of the sewer (in gpm) when it is flowing full ... 

Figure 8.3 shows that the sewer is full flowing at 775 m3 h 1 (215 L s 1). It also shows that the reaeration and the DO concentration vary considerably with the flow conditions. At rather low flow rates, the DO concentration is about 2-4 g02 m-3, a level that is significantly reduced even at flow rates that are below those corresponding to a half-full flowing pipe. Example 8.2 shows that it is possible to control the magnitude of the aerobic transformation of the wastewater by the selected level of the flow compared with the capacity of the sewer. 

The availability of a sanitary sewer near the point of chlorinated water release, and the capacities of the sanitary sewer and the wastewater treatment plant to handle the additional load, are the primary limitations in this method. Potential upset of treatment plant operations due to chlorinated water release must also be evaluated. A back-flow prevention device or an air gap method must he used to prevent cross-connection problems. 

Sewers, in general, are designed for gravity flow. In a tightly sealed system, a rise in water level will reduce the vapor space and cause an increase in pressure. Such a tendency will, in turn, reduce the sewer s design capacity. Under these circumstances, vents are necessary to release vapors and to prevent vapor lock. Vents are functionally designed to maintain atmospheric pressure in the sewer and to release vapors to safe locations. 

Figure 8-9. Capacity of sewer pipes running 3/4 full. Sizes 4-inch to 24-inch inclusive. Turbulent flow e = 0.00085. Darcy formula Q = 19.65 fh[5"...

N-5 Septic Tank. The septic tank and drainfield making up Sewer System V are located south of building 1117-N and were installed in 1981 the system was taken out of service in February 1987 (OOE-RL 1990). Sewer System V serves buildings 1111-N, 1116-N, 1117-N, 1118-N, 1123-N, 1124-N, 1125-N, and 1131-N. The septic tank has a fluid capacity of 14,000 L (3,677 gal) and a drainfield providing approximately 90 m (960 ft ) of infiltrative surface area. Fill dirt was placed over the drainfield to a depth of 0.6 m (2 ft) or more in the early 1980s. In 1985, the unit served 210 personnel and the calculated daily flow was 140,000 L/day (3,780 gal/day) (DOE-RL 1990). The sewer system is still in place it is unknown if residual liquid is present. 

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