Developing a monitoring network for Waterstreet’s living lab

Abstract

Sustainable Urban Drainage Systems (SUDS) are useful tools to manage rainwater and reduce pollutants in urban environments. Their use, as sustainable solutions, can mitigate the effects of climate change and urbanization. The existence of different definitions of performance is one reason for delaying more implementation of SUDS. Deciding on the Key Performance Indicators (KPIs) is one of the objectives of this thesis. WaterStreet, the chosen study area, is a living lab that permits the implementation, presentation, and testing of newly designed SUDS with the goal of facilitating their entrance into the market. WaterStreet could benefit from using sensors to provide the KPIs and other indicators of performance, but the sensors already implemented do not achieve that objective fully. So, the objective of this thesis is, to develop a comprehensive set of KPIs that describe the performance of SUDS and propose a monitoring network to measure the performance of SUDS implemented in WaterStreet.
To achieve that objective, information on the study area’s characteristics, like soil types, design of SUDS, and groundwater levels were gathered to find how water flows in, out, and around the study area including the SUDS. Additionally, the key stakeholders were determined with a stakeholder analysis, and literature was researched on the important indicators used to reflect the performance of SUDS for water quality and quantity. Interviews were performed to include the view of the key stakeholders on the indicators found in the literature. The two approaches explained above provide the data that need to be monitored on WaterStreet. Criteria for the quality of data that would be provided by the sensors are set, before concluding on suggestions. The suggested sensors and their limitations are based on results of published studies and reports.
Based on the findings of this thesis a distinction between the Key Performance Indicators (KPIs) and Indicators of Performance (IP) is made. In the first category, the indicators of overflowing volume, duration, and frequency are included along with rainfall and overflow from upstream drainage areas. In the second category the indicators, infiltration in the soil and through the first layer of SUDS, and storage in the soil and system are included. Both categories of indicators are suggested to be monitored in the study area of WaterStreet to increase the value of WaterStreet as a living lab. Indicators for water quality are not concluded due to the lack of information on the existing pollutants and their removal and remobilization mechanisms. Reduction of Total Suspended Solids (TSS) and Total Phosphorus (TP) are two possible indicators that are also considered as a proxy in Germany. Changes in pH and temperature are two indirect indicators that are found to affect the reduction and remobilization mechanisms and are therefore important to consider as well.
An acoustic disdrometer to measure rainfall, a sonar pulse sensor to measure groundwater levels, divers in an observation pipe in the system to measure the water level in the system and the infiltration in the soil, and lastly divers in a controlled volume downstream of the SUDS to measure the overflowing water downstream the SUDS, were the proposed sensors. The disdrometer and two of the sonar pulse sensors are already installed on WaterStreet while it is suggested to put divers in the individual systems and two more sonar pulse sensors. For the indicators, overflowing water from upstream and the rate of water entering the SUDS research on the runoff coefficient and the use of water balance are suggested, respectively.
An important consideration in this thesis is the characterization of hydraulic isolation from the top and bottom of the system, allowing the interpretation of the data from monitoring, to represent only one system’s response. Suggestions to include a controlled volume to capture the overflow downstream of the SUDS and a drainpipe to ensure a drainage depth of 0.5 m, are made, to help ensure hydraulic isolation from top and bottom respectively. Based on this study, only half of the systems placed on WaterStreet are isolated, not considering the possibility that the groundwater table can get even higher resulting in even fewer systems isolated. Additionally, from analyzing the hydraulic response on the SUDS in WaterStreet, it was concluded that all 5 studied systems out of 8 total were being over-dimensioned, meaning that the storage in the SUDS would not be full even with rainfall of once in 100 years. From the same analysis, it was also concluded that the infiltration through the first layer is the prevalent overflowing mechanism of 3 out of 4 studies SUDS. Both the previous findings are important to realize a hydraulic response to rainfall proportionally to real implementations. This is an essential consideration from living labs because they try to bring lab and real implementation closer. Lastly, pollutants to be used as KPIs for water quality performance of SUDS should be researched more based on the principle of not shifting problems downstream.