Flow Survey (Natural / Urban)
EMS carries out flow gauging in rivers, streams and manmade channels culverts and other constructed channels. Different equipment is appropriate to different situations, from small area velocity probes to pulse-Doppler instruments capable of measuring flow fields accurately up to 7 metres deep. Clients are often consultants or statutory authorities, with the results contributing to hydrological studies. Increasingly, flow survey requirements are for hydro-electricity schemes.
Reported Information
Flowrate, velocity, and depth information is recorded at time-steps of several minutes. This information is reported back to the client in detailed and summarised form including daily minimums, maximums, averages and totals.
Data is usually collected over a number of weeks to capture significant events and a range of conditions.
River Gauging
River gauging often involves the siting of several instruments across a river cross-section. These measure flow depth and velocity through the water column. The cross-section is measured so the relationship between depth and flow area is known allowing measurements to be resolved into flowrates. Cross-sections are chosen carefully to avoid re-circulations and moving river beds. In difficult circumstances, dilution gauging is used.
Rainfall
Local rainfall information may be required. In this case, rain gauges are sited appropriately around the site to record at the required interval.
Water Quality
Some flow surveys have requirements for the collection of water quality data. EMS have multi-parameter instrumentation that can be deployed to collect continuous data a combination of temperature, pressure, pH, turbidity, conductivity, DO (dissolved oxygen), ORP (Oxidation Reduction Potential), ammonium, chloride, nitrate.
Other parameters, e.g. BOD, COD, suspended solids, or very specific chemical parameters, can be determined by sampling using automatic samplers, and subsequent lab analysis. This can all be built into the survey.
Remote Monitoring
Flow and water quality data can all be streamed over the internet for deployments where immediate review is required. Clients use EMS’s portal facility to view data which can be pushed regularly (e.g. every 15 minutes).