Combined sewer overflow sensor system and methods

A system (1) for detecting an overflow event in a combined sewer (2) comprising: a sensor (101) for detecting the height of water in the combined sewer (2), the sensor (101) being a non-contact level sensor positioned at a height above an overflow outlet (201) of the combined sewer (2), a controller (102) adapted to receive sensor data from the sensor (101), an on-board power source (104) for providing power to the sensor (101), the controller (102) and the transmission module (103); and, wherein the system (1) is configured to operate in two modes, a coarse detection mode, and an overflow detection mode; and, wherein, in the coarse detection mode the system (1) is configured to detect the level of water in the combined sewer (2) at an interval of t (detection) coarse, and wherein in the overflow detection mode the system (1) is configured to detect the level of water in the combined sewer (2) at an interval of t (detection) overflow, wherein t (detection) overflow is less than t(detection) coarse·