REV02485 - Laserfiche WebLink

Home Browse Search

Sellartls 8 Grigg, Inc The calculations assume that the two reaches of pipe operate independently. That turns out to be a correct assumption. However, since the proposed system is closed from the Mine to the outfall, the calculations should also be checked as a single system to verify that the system is not a siphon. S&G has provided these calculations. The capacity of the pipe is high relative to the demand. The portion of the drainpipe to be installed at 2-percent gradient will not flow full. The flowing water will tend to drag the air above the water along the pipe thereby creating a reduced, sub atmospheric pressure in the pipe. This reduced pressure may cause the water surface to contact the top of the pipe at intervals. A pulsating flow capable of damaging the system, especially the outfall, may result. To avoid this scenario S&G recommends that a vent be added to the high point of the system to provide replacement air and establish atmospheric pressure. To ensure enough air and to reduce excessive velocities and attendant noise, the vent pipe should be at least 6-inches in diameter. A screen over the vent should be provided to inhibit vandalism or the entry of wildlife into the system. The intake will be inaccessible to maintenance after construction and yet must continue to operate. S&G recommends a screen or debris fin over the intake inside the Mine. The calculations are based on an unobstructed protruding pipe inlet. A pipe inlet protruding into the Mine from the top is good. Heavy debris and sediment will collect on the Floor where it will not compromise the intake. Floating debris such as plastic bottles that may have been left in the Mine will collect on the ceiling. Such debris could collect at the intake. The protruding pipe will inhibit the collection of such debris at the intake. However, over time if enough floatables collect or if marginally Floating objects are washed with the current, the intake could become plugged. A debris fin or screen would help prevent the formation of a watertight plug. The calculations are based on a free discharge at the outfall without tailwater. The outfall of the pipe should be above the inlet or crown of the culvert under west lanes of the highway. This reduces the chance for a tailwater caused by the culvert inlet during a storm. In addition, should the highway culvert become partially filled with silt, the outfall would be less likely to become blocked. The chance of a backflow from the highway median into the Mine would be reduced. The vent recommended above would also reduce the likelihood of such a back flow. If and only if the screens recommended above are installed, S&G recommends a removable or hinged screen at the outlet to prevent wildlife from entering the system. It is worth noting that boring under the highway and accurately holding proFlle is a difficult job. Only a qualified Contractor should perform this work. CONCLUSIONS SSG believes that the system as designed by J.E. Stover & Associates is a system that will perform as designed. In order to prevent or reduce the chances of a malfunction, the system can be improved with the addition of several features including the following: 1. A vent (with a minimum diameter of 6-inches to avoid whistling) at the high point of the system, 2. Screens at all openings including the intake inside the Mine, 3. A protruding inlet near the roof of the Mine, and 4. Location of the outfall at or above the crown of the highway culvert. 390 Union Boulevard. 303.986.7444 Suite 630 FAX 303.986.0994 Lakewood. Colorado 80228 E-MAIL wvrv.sandg4.com