Watershed Symposium 2017

Tracking Urban Water Flow Using Stable Isotopes of Water

Summary:
With increasing population and water demands, water managers are utilizing local, non-local and recycled water to supply urban water systems. Using water isotopes, here we present a novel way of tracking different water sources in an urban system, which is extremely important in context of water rights and contamination issues.

Full Abstract:
Stable isotopes of water have extensively been used to understand hydrological cycle in natural environment, however their application in highly managed urban water systems have been limited. Recent research has shown that water isotopes reflect urban water management practices and have potential application in understanding urban water supply network dynamics, evaluating effect of climate variability on water resources, geolocation and water monitoring and regulation. Previous work has highlighted strong and structured spatiotemporal variation in tap water isotope ratios of Salt Lake Valley (SLV) which has been attributed to complex distribution systems, varying water management practices and multiple sources used across the valley. Building on these observations, we collaborated with the largest water supply company in SLV, Jordan Valley Water Conservancy District (JVWCD) and expanded our project which now includes predicting the source (or sources) contributing to a given supply area. The different sources supplying JVWCD (such as Provo River system, Wasatch Creeks and groundwater wells) have similar yet distinct isotope ratios, providing an excellent opportunity to test the robustness of water isotopes in monitoring distribution pattern of the sources in the supply system. For this project, we collected more than 100 samples/month (between April 2015-May 2016), from different water sources (creeks, streams and groundwater wells), water treatment plants (WTP), storage reservoirs and delivery locations along the supply lines across the water distribution area, measured their isotopic ratio and developed isotopic mixing models using Hierarchical Bayesian (HB) framework to connect the different sources in the system to their supply area. In this study, we have used water isotopes to quantify the proportion of water supplied by different sources at various locations within the supply system. We have explicitly incorporated volumetric and spatial effects to constrain the contribution of each source, thus addressing identifiability issues associated with partitioning multiple sources with only two isotopes (δ2H and δ18O). Our initial results are in close agreement with those obtained by physical models used by JVWCD. Our result suggests that isotopes open a new line of investigative technique to analyze urban water systems which does not require details of the supply system information. HB isotopic models can be extremely useful in systems where the supply information is missing, or are proprietary. In general, comparing the results from the isotope model can help improve the robustness of the existing physical models. Considering the fact that isotopic measurements have become fairly easy and cheap, coupling the physical supply models with isotope data in future can make urban water supply systems analysis more robust and accurate. The only requirement for robust estimates from isotopic models is the presence of sufficient isotopic variations between the different sources in the system. In systems with sources having comparable or similar isotope values, the robustness of the estimates will be questionable.