There is an automatic valve that monitor’s pipeline velocity and automatically closes if there is a major break in the line, in fact there was an automatic valve installed at the base on the 2 million gallon tank in 1979 and 1980. The problem is that the valve cannot differentiate between a broken pipe and high fire flow demand. If there is a large fire the valve may close thus shutting off the water supply for firefighting purposes.
Our calculation indicate the maximum discharge from an open 12-inch pipe with the pressure created by a full tank is about 6,400 gallons per minute. In 30 minutes that would be 192,000 gallons. In reality the leak would start smaller and the Town would shut off the valves on both sides of the main before that much water was discharged.
Steps to Reduce Complete Loss
The Town has taken several steps to help reduce the complete loss of the 2 million gallons of water as noted above, we have an automatic valve at the base of the 2 million gallon tank and we have installed 2 isolation valves and 2 fire hydrants on each side of the landslide area as means to help shut off the 12 inch waterline main. Please be aware if the 12-inch waterline main is damaged and with the water pressure between 80 and 90 pounds it will leak 6,400 gallons per minute and will damage a large area in Broadway travel lanes. There are a few variables that also could have impacts to this area:
- Major water infiltration into the scrap
- How full the 2 million gallon tank is
- How quickly Town crews can respond and shut down the broken 12-inch water main with the 2 isolation valves