A Lesson from Arid Regions Sand Dunes: Structured Mini-Dunes (SMDs) as Sustainable Irrigation Units

Eco-hydrology of natural dunes is studied by design and construction of texturally structured mini-dunes (SMSs, height < 1 m) which are tested as sustainable irrigation units. Mini-dunes can intercept moisture from a humid ambient air or shallow water table (e.g. in sabkha landforms). Ornamental plants or crops can be cultivated at the crest with minimum irrigation quantities/frequencies. In this paper, two SMDs of a conical shape (150 cm in base diameter and 45 cm high) were constructed and tested in the field under a controlled subjacent water table. SMDs are similar to natural mini-dunes, called “Nabkhas”. SMDs’ core soil was a medium sand (d50= 0.25 mm) for SMD-1. In SMD-2 the core soil was shielded by 5 cm thick coarser sand (d50= 0.7 mm). Soil moisture sensors were placed at the depths of 25 and 75 cm to monitor the volumetric moisture content (VMC). After two months, VMC in the lower sensors was almost the same (0.186 m3/m3). However, in the upper sensors, SMD-2 had a VMC about two times higher than SMD-1. The average VMC in SMD-1 and SMD-2 was about 0.074 m3/m3 and 0.1 m3/m3, respectively. Evaporation through the SMD-2 soil composite was simulated by HYDRUS2D for 15 days. HYDRUS2D findings are substantiated by the experimental results. This qualitatively agrees with the hypothesis that the course sand-gravel sheath (tilted and horizontal) acts as a capillary barrier, similarly to one found in large dunes. SMDs are advocated for cultivating plants in arid regions, especially in areas with shallow unconfined aquifers. Plants cultivated in SMDs are expected to have higher water use efficiency as compared with ones in “flat topographies”. Our design can be a new way to revegetate the arid deserts and sabkhas.