D6.4. Space distributed monitoring and data interpretation

This document is a deliverable of the Co-UDlabs project, funded under the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101008626.

The study described in this deliverable shows the potential of analysis of large spatially distributed (open) urban drainage data sets and how this may impact on regulatory policy, water utility behavior and people’s behaviour.

This deliverable report compares two types of decentralized assets: Combined Sewer Overflow (CSO) structures, and Sustainable Drainage Systems (SuDS). This is because CSO structures have come under increased scrutiny during the process of review and recast of the Urban Wastewater Treatment Directive (UWWTD) and openly available CSO spill data is becoming available in some regions. Large storage facilities (tanks), SuDS structures and real-time control are the main technical solutions to reduce CSO spills. Widespread spatial analysis of monitored SuDS performance currently does not happen. Hence this deliverable tries to take lessons learned from analysis of spatial CSO performance data and CSO related regulation and discusses what this may mean for the management of SuDS structures.

The existing Water Framework Directive (WFD) requires the combined control of point and diffuse sources, with establishment of emission control based on best available techniques or relevant emission limit values, and best environmental practices in case of diffuse pollution. The original UWWTD (1991) specified the monitoring of Waste Wastewater Treatment Works (WWTW) performance. A comparison of CSO related data collection and regulation between 10 European countries and regions has shown that this has led to a plethora of local regulations and guidelines around managing CSO performance. Assessing CSO compliance using monitored data does not happen in most countries/regions. The local regulations can be broadly divided into two types, emission based (limiting CSO spill frequency or spill pollutant load) and receiving water impact based (limiting concentration-duration-frequency of indicator pollutants in rivers). This, however, leads to a conundrum as data for simple versions of emission-based regulation such as spill frequency is relatively easy to collect but does not inform about the receiving water quality, whereas harm caused by CSO spills on the receiving water is so complex to monitor and simulate that this process is opaque and regulation becomes practically almost non-enforceable.

Analysis of the open annual CSO spill frequency and duration database from England and Wales has indicated the difficulty of trying to derive relationships between physical and socio-economical parameters and spill durations, although some correlation existed between rainfall amount, catchment steepness and duration of spills. The establishment of this open database did, however, lead to the highlighting large amounts of spills as well as the considerable investment needed to upgrade and future-proof decaying drainage systems. The recast UWWTD calls for more open performance data. Even simple but widespread (open) data can be very beneficial, for example it allows quickly noticing CSO spills occurring during dry weather. However, data should be made open with due care and in collaboration with local citizens' interest groups, social scientists and governance experts.

In several other countries, the exact number and location of all CSO structures is not known at national or regional levels, and several countries also do not have legally binding CSO emissions regulation, which makes detecting unsatisfactory spills and subsequent improving of unsatisfactory CSO structures difficult. The complexity and cost related to checking CSO compliance with receiving water impact standards means we lack oversight data concerning CSO compliance and impact on receiving waters. Inventory and performance data of SuDS structures is not widely and routinely collected, a main concern is that in several decades it will be extremely difficult to even find out where SuDS structures are and who maintains them.