A Low-Cost Water Depth and Electrical Conductivity Sensor for Detecting Inputs into Urban Stormwater Networks

Abstract

High-resolution data collection of the urban stormwater network is crucial for future asset management and illicit discharge detection, but often too expensive as sensors and ongoing frequent maintenance works are not affordable. We developed an integrated water depth, electrical conductivity (EC), and temperature sensor that is inexpensive (USD 25), low power, and easily implemented in urban drainage networks. Our low-cost sensor reliably measures the rate-of-change of water level without any re-calibration by comparing with industry-standard instruments such as HACH and HORIBA’s probes. To overcome the observed drift of level sensors, we developed an automated re-calibration approach, which significantly improved its accuracy. For applications like monitoring stormwater drains, such an approach will make higher-resolution sensing feasible from the budget control considerations, since the regular sensor re-calibration will no longer be required. For other applications like monitoring wetlands or wastewater networks, a manual re-calibration every two weeks is required to limit the sensor’s inaccuracies to ±10 mm. Apart from only being used as a calibrator for the level sensor, the conductivity sensor in this study adequately monitored EC between 0 and 10 mS/cm with a 17% relative uncertainty, which is sufficient for stormwater monitoring, especially for real-time detection of poor stormwater quality inputs. Overall, our proposed sensor can be rapidly and densely deployed in the urban drainage network for revolutionised high-density monitoring that cannot be achieved before with high-end loggers and sensors.

Illicit discharge detection in stormwater drains using an Arduino-based low-cost sensor network

“…On average, 22 maintenance trips were conducted during the study period for each site (i.e., approximately once every two and half weeks). This maintenance frequency is in line with the low-cost depth sensor's manual recalibration frequency suggested by (Shi et al 2021).…”

“…BoSL boards have all the existing functions of an Arduino MCU at reduced power consumption, which achieves a lifetime between six months to one year by using a 3.7 V 11.2Ah LiIon battery. An all-in-one water level, temperature, and EC sensor (Shi et al 2021) also replaced the separate sensor system used in the first version to reduce its preparation and installation time. The sensor unit including the data logger, the all-in-one sensor, and the battery, together costs around USD 150.…”

“…As such, online methods have mainly been used for research and small-scale studies due to budget limitations of IDDE programs from municipalities or water authorities. To overcome the existing disadvantages of such online sensor methods and leverage their potential benefits, Shi et al (2021) developed an Arduino-based low-cost sensor that measures water level, temperature, and electrical conductivity. The sensor is easy and relatively cheap to install and connect to a broad range of microcontroller units for real-time data collectionmaking it substantially more feasible to install sensors throughout stormwater drainage networks to isolate dry weather flows to practical drainage lengths for follow up inspection.…”

“…This study aims to develop a systematic approach based on this low-cost sensor technique (Shi et al 2021) to assist with the illicit discharge detection and elimination in urban stormwater drains. The objectives of this study include: (1) verify the lowcost sensor's performance in real-time detection of dry weather discharges; (2) understand the characteristics of dry weather discharges including their frequency, duration, and intensity for different land uses and predict potential sources; and (3) evaluate the efficacy of such a spatially distributed sensing network to isolate dry weather discharges and support appropriate management responses.…”

Towards the long term implementation of real time control of combined sewer systems: a review of performance and influencing factors

“…However, it can be used to monitor in-sewer processes (Ebi et al 2019) and application to industrial control systems is being tested (Hoang et al 2020). This combined with recent advances in cheap sensor (Shi et al 2021) can lead to increased potential of decentralised control.…”