Stage - discharge
The Providence Stormwater Innovation Center is measuring the volume of water flowing into and out of the park pond system. This information combined with data on the concentration of pollutants allows us to calculate the pollutant loads entering and leaving the pond system to assess whether the BMPs are working effectively.
A streamflow gauging station is established by developing a relationship between stage (water level) and discharge (streamflow) at a selected cross section site. Discharge can't be measured continuously, but water level can be measured continuously using pressure sensors in the stream that log and store values.
A relationship between stage and discharge is developed by taking direct streamflow measurements over the expected range of discharge and stage. Each flow measurement and corresponding water level is then plotted and a smooth curve is drawn that is used to calculate continuous discharge. The stage-discharge rating curve can be used with a continuous water level record to produce a time series of discharge for the period during which water level has been recorded. A stage-discharge graph allows for discharge computation with any stage value.
The streamflow in and out of the park can be assessed to complete a water balance. Weekly and storm sample analysis of phosphorus (P) and nitrogen (N) will be used to calibrate a spectro::lyser sensor used to measure continuous nitrogen and phosphorus concentrations. Coupling the streamflow data with sensor data, continuous nitrogen and phosphorous load can be calculated and thus the nitrogen and phosphorous flux into and out of the park. Reduction in pollutant load is often an important measure of success in non-point source watershed projects.
The map below shows the two locations that have been identified, near the inflow and outflow of the ponds to continuously monitor stage (water level) and associated discharge (streamflow).
The Providence Stormwater Innovation Center will be selecting 5 individual BMPs to monitor water levels at the inflow, in the infiltration basin, and in the outflow. This is done to estimate volume of stormwater being treated in each BMP and get a better understanding of percentage of pollutants being removed. This monitoring will also provide information that the BMP is functioning properly during rain events. The map below shows the selected BMPs for stormwater volume monitoring
Measuring rainfall is an important parameter in estimating volume of stormwater treated and pollutants removed by stormwater BMPs. The Providence Stormwater Innovation Center will use a tipping bucket rain gauge to measure rainfall in Roger Williams Park. Having a rain gauge in the park provides better accuracy of precipitation by monitoring localized rain event