Did you know? All about flow monitoring!

Rainfall and Sewer Flow Monitoring

Rainfall quantity (total rainfall in a storm event) and intensity (rate of rainfall) drive the ability of the landscape to absorb rainfall, and the quantity and intensity of stormwater runoff that drains through streams and combined stormwater and sanitary sewers. The ability of landscapes, streams, and sewers to absorb and convey stormwater is being modeled under existing and proposed (improved) conditions. In order to calibrate sewer flow response and combined sewer overflow (CSO) computer models to real-world conditions, rainfall (at 10 locations) and sewer flow (at 17 locations) are being monitored every 5 minutes over a 6-month period.

Sewer Flow Monitoring

Sewer flow is being monitored every 5 minutes at 17 locations that are representative of a range of types and sizes of surface and sewer watersheds (“sewersheds”). Sewer flow monitoring is done using automated instruments that track the depth and velocity of water in the sewer, and using pipe geometry (slope, shape, and roughness). Sewer flow data is collected, stored, then sent in packets of data to a centralized data server using cellular data telemetry.

Image of a flow monitor inside a sewer pipe. Several of these were placed throughout the Four Mile Run sewershed. This example is from the Woods Run sewershed.

Rainfall Monitoring

Rainfall is highly variable over time and across the watershed, and is expected to show differences among locations depending on the type of storm (see example below). For example, summer thunderstorms can be very focused and result in heavy rain in some areas while other areas, sometimes less than a mile away, receive little or no rain. To account for this storm variability and facilitate interpretation of sewer flow in light of localized, subwatershed rainfall quantity and intensity, a network of 10 rain gauges has been established within the project watershed/sewershed as shown in the figure below. Rainfall data is collected in 0.01-inch depth increments, and is stored, then sent in packets of data to a centralized data server using cellular data telemetry.

Image of a rain gauge on a rooftop at Carnegie Mellon.

 

Rain Gauge Comparison Graph

An example of location-to-location rainfall variability presented as cumulative rainfall hydrographs. Note that rain gauge locations with greater rainfall quantities vary among locations and from storm-to-storm.