Hex-Urban: Investigating the adoption of hexagonal grids to represent the total urban water cycle within a distributed water balance model

Abstract

With urbanization and climate change, the reliable water supply by centralized system is facing challenges. Research on the (re)use of the outflow from an urban area as an alternative water resource is increasing in recent years. This research requires spatial and temporal information on the status of components of urban water cycle. Several hydrological models exist for the purpose of urban water management. However, none of them considers modeling the total urban water cycle by a water balance approach in a spatial explicit manner. Distributed Urban Water Cycle Model (DUWCM) is developed in this thesis to investigate the benefit of a scalable and efficient water balance model that simulates the rainfall-runoff system and water supply-wastewater system in urban areas. Two case studies were carried out to verify the model and demonstrate the capability of modeling a large hydrological catchment respectively. DUWCM is developed as adaptable to a planning-support tool UrbanBEATS. Spatial representation of the second case study will be provided by it in squared and hexagonal tessellation. Hexagons have been applied in many spatial modeling fields, while rare applications can be found in water balance modeling. A comparison of model results from squared and hexagonal grids is done in this study. The comparison demonstrates that the difference in flow direction and sampling of the land cover ratio between square and hexagon blocks results in obvious differences in the location and the magnitude of peak flows. Since hexagonal grids perform better in flow path simulation (de Sousa et al.,2006), it is expected to be preferred over squared grids in distributed hydrological models. Thus, DUWCM, being scalable in the number of blocks and shapes, has the potential to be widely applied in sustainable water management.