Interplay of Sediment Transport and Urbanization in Wadi Environments

The land surface within a wadi is mainly shaped by natural events and anthropogenic intervention. Sediments are transported and deposited by natural forces, aeolian or hydraulic. In many regions, human activity has become an additional major driver interacting with the forces of nature to reshape the wadi landscape. The interplay between natural and anthropogenic drivers is most significant in metropolitan development with rapid urbanization. In arid/semiarid climates collisions occur due to the different timescales of the developments. Urbanization is progressing continuously in comparison to the effects of sporadic storm and flooding events. Urban development is fast in the sense that major changes can often be observed in the hydrological quiet period between two natural events. We outline the general development and illustrate two special case studies concerning intertwined development of sediment transport and urbanization at various locations in Oman using satellite images and data from figure-ground maps. Changes of sediment distributions, erosion and deposition, are examined before and after flooding events. For selected localities we illustrate and discuss the human reactions after the last event – and before the next. Regional effects like change of flood streamflow due to the development of infrastructure, sealing of land surfaces, change of land use as well as land subsidence are highlighted. The chosen examples show that changes in sedimentation patterns may be caused by severe single events, like cyclones, or as effect of slow processes, like erosion of a flow channel. The nature of such changes is not always well understood. We show in one of our examples how urban planning and urbanization had the wrong focus for a long time and we recommend to change this.