Sustainable Management of Water Resources in Matmata

In the study area, agriculture, despite being rainfed, constitutes the main core of the region's economy because it helps to fight against food insecurity, unemployment, and environmental degradation. It is based on traditional techniques and under the effect of competition between the different water users. Therefore, their agricultural yield is relatively very low. Improving productivity and resolving conflicts is one of the surest ways to achieve food self-sufficiency, control migration, reduce unemployment and protect the environment.

At this level, the focus will be on (i) Optimizing irrigation in the "Matmata 5" irrigated perimeter

We propose to support farmers to save water through smart irrigation at the "Matmata 5" irrigated perimeter.

The farmers in this irrigated area use traditional irrigation based on watering crops manually. It is quite simply a waste of water, energy, and farmer time (unprofitable, and uneconomic). To overcome this situation, it is advisable to use smart irrigation systems. The system consists of monitoring the parameters of the water profile of the soil using the installation of soil moisture sensors, flow meters, solenoid valves, and a weather station to collect the meteorological data.

In addition, the system requires the creation of a Smartphone application "It’s a platform". This application or platform receives information from sensors and sends recommendations to farmers to irrigate or to stop irrigating.

(ii) Ensuring equitable and effective surface water use (Reducing conflicts)

At the scale of the spreading perimeter, we propose to develop a plot plan for the rehabilitation of the spreading perimeter. The rehabilitation of the perimeter begins with the shaping of the plots, in particular the dykes and spillways, and the distribution channels similar to those that existed before the revolution (2011) to ensure equitable and efficient use of surface water. 

Figure 1. Floodwater diversion structures and spreading perimeter of new Matmata (Photo: Abdelli, 2012) 

to reduce the upstream (Wadi Jir basin) - downstream (spreading perimeter) water use conflict, we suggest developing scenarios of optimal water allocation using hydrologic simulation.

To ensure the replenishment of the main aquifer of the region, a comprehensive soil and water program has been implemented since 1990 in the framework of the national strategy for water resources mobilization and soil conservation (Min. Agr., 1990a, b). Check dams have been installed with the aim to mobilize additional resources for the aquifer through recharge with floodwater (Yahyaoui et al., 2002) and to protect people and infrastructures during flooding disasters. In fact, Check dams have recently been widely used in the Wadi Jir watershed for floodwater harvesting in this area. After heavy rainfall storms, temporary ponds (up to 2 m deep) are formed which increase the opportunity time for the water to infiltrate through the deep layers into the aquifer.

These interventions, especially in the upstream of the watershed, have generated an imbalance in the distribution of runoff water between the upstream part and the downstream part. The CRDA technicians, responsible for monitoring the effect of these new WHTs, confirm this upstream-downstream disparity. In fact, they reported that before the creation of the gabion structures, a rain of 40 mm drained the Jir wadi and irrigated the spreading perimeter in the downstream part. Now, after the planting of the gabion structures, with the same amount of rainfall, all the water remains trapped upstream, so the spreading remains dry. The water arrived at the spreading perimeter only for rainfall of more than 60 mm. In addition, investigations with local residents show that the gabion structures have remarkably reduced the quantity of water flowing into the wadi that reaches the spreading area, especially for rains of less than 60mm. Then, considering the problem of water scarcity aggrieved by climate change, it is an urgent task to develop a decision support system that helps to reconcile upstream with downstream interests. in this context, we must take into account the water requirements of the spreading perimeter and also the water that must be allowed to flow in the natural wadi bed to the Mediterranean sea. 

Figure 2. Upstream-downstream conflicts

ii) Evaluating the potential impact of generalizing water-saving technologies (underground cisterns) to mobilize water.

The arid zones of Tunisia are devoid of surface water, underground water is inaccessible because it is very deep. Shallow aquifers are very limited in quantity and have poor quality.

The situation is expected to worsen due to the effect of climate change. One way to support this vulnerable situation is by increasing the water supply. Throughout centuries, society in this dry area has learned to cope with water scarcity. Cisterns called Majel (private property) and Fesquia (communal property), are reservoirs used for storing rainfall and runoff water for multiple purposes: drinking, animal watering and supplemental irrigation. This technology remains one of the best WH to mobilize water. In fact, it is estimated that a tank with a capacity of 35 m3 can meet a family's and its livestock's annual water needs (Ennabli, 1993). Due to the higher cost to create a cistern and the maintenance costs, this system towards abandoned. There is a need to address the efficiency of this system in terms of food production (impact on local agricultural products) and water availability (impact on the amount of water harvested). 

Figure 3. Underground cistern (Majel) for supplemental irrigation in Matmata region (Photo: Abdelli, 2019. Sketch: adapted from El Amami (1984))