The primary use of storm tanks is to prevent flooding and pollution. Inland storm tanks can be used to expand the capacity of combined sewer networks during high flow periods such as rainfall and are a good solution for locations subject to DG5 flooding orders. On surface water systems storm tanks are also used to reduce the risk of flooding, again providing extra capacity during rainfall. In the wastewater industry the storm tanks can also be used to regulate the flow into a sewage works during rainfall and at CSO overflows to minimise the frequency of discharges.
There are three types of storm tanks, the full containment, attenuation and re-circulating. Full containment typically are retrofitted within a sewer network and include a weir that during high flow caps the peak level of flow. Being a retrofit they often are lower than the original sewer network and hence have to be emptied manually by either a tanker or a pump back into the main sewer network. Hence the remote monitoring of the level is a major advantage.
Attenuating storm tanks are ones that include a restrictor valve (pre-set) to limit outflow again in order to cap the peak flow down stream. Here monitoring is important as it is possible the output could become obstructed and/or the output could be incorrectly adjusted leading to the tank becoming full resulting in a spill or flood.
Recirculation storm tanks are similar to attenuation, however the output is often controlled by a control valve with and the output fed back into the network when the flow is low.
The Importance for Storm Tank Monitoring
The effectiveness of any storm tank during a rainfall event is related to its available storage capacity. Hence it is easy to see the benefits of being able to remotely monitor the available capacity of a storm tank in order to plan emptying and in the case of attenuation tanks to optimise their operation.
Fully compatible with the BDT and FDT technology, Radio Data Networks STM System is a real-time monitoring solution for Storm Tanks. Using hydrostatic pressure measurement technology the system derives the depth and hence available capacity from the level of stormwater.
The system is ideal for installation to both new and existing storm tanks, both closed and open. Preferably the pressure transducer suspended into the storm tank within a stilling tube (a section of perforated pipe) that both provides mechanical protection and reduces turbulence within the tank.
Above the storm tank is mounted the STM’s radio transmitter. In the case of the tank in the example photograph the transmitter is located in the void between the storm tank’s cover and the manhole cover.
In operation the STM transmitter applies power to the pressure transducer every 5-minutes, however just like a BDT the level is then repeatedly transmitted at 2.5 second intervals.
The nearby Booster/Repeater mounted above ground picks up the message and relays it back to the Gateway Receiver, where the Gateway is equipped with a 4-20mA output card converts the signal back into an analogue level for interface to the telemetry / SCADA.
In summary, correctly used the STM can help deliver a significant reduction of flooding through triggering advanced tank emptying. Similarly for attenuation tanks it can be used demonstrate the actual storage rate and to warn of outflow blockages. Finally, the system can be used to reduce carbon footprint through targeted emptying.
For more details of the STM and similar RDN systems please call +44(0)1279 600 440 or e-mail sales.