Traditional environmental knowledge and transport efficiency of a communal canal network, Tafilalt oasis, Morocco: A historical GIS analytics perspective

Abstract

The provision of water in the arid Tafilalt – the largest natural oasis in Morocco – changed little over a span of centuries, though the network of surface canals and khettara (qanats) gradually expanded to yield more water to a growing oasis. The introduction of newer water technologies (pumped wells and dams) in the 1970s reduced the availability of water to the oasis but has not diminished reliance on the traditional canal network. All agriculture in this Sahara oasis is irrigated and most water is still distributed through an intricate system of earthen canals incrementally built over centuries and maintained to this day. Here, a traditional environmental knowledge (TEK) and transportation GIS framework is used to explore the efficacy of this common property canal network. Aerial photographic and field survey, interviews with users and managers of canal waters, and GIS network analysis were employed to examine the functional characteristics and communal issues inherent in the canal system, and to assess the efficiency and effectiveness of the traditional system as a water delivery network. GIS analytics employed to assess the distributive utility of the canal network include the Detour Index, Alpha Index, Beta Index, Gamma Index, and Network Density. The first four indices address the efficiency and connectivity of the complex canal network while Network Density assesses the effectiveness of the system in distributing water throughout the oasis. Results demonstrate the strength and adaptability of local TEK, revealing that the historic canal system was incrementally but not haphazardly constructed, and the system that evolved exhibits an efficiency of water distribution closely approximating the efficiency that could be obtained using advanced design and modern planning methods.