The Effectiveness of Continuous Contour Ridges and Intermittent Trenches Constructed Using the Vallerani in Water Harvesting in Arid Regions

Rainwater harvesting (RWH) is the most economic and sustainable management method utilized to overcome the problem of water penury in arid regions. Jordan is one of the countries in the Middle East most suffering from water deficit since more than 80% of the country’s area receives 50-150 mm of annual rainfall. Different water harvesting techniques (WHT) have been used in many countries in arid and semi-arid regions. An evaluation experiment was conducted at two sites; one is at Al Mwaqar, southeast of Amman, and the other is at Al Grain, west of Al Azraq city. The objective of the current research is to evaluate and determine the effectiveness of two water harvesting techniques constructed by the common Vallerani system using continuous contour ridges and intermittent trenches (bunds) upon effective rainfall (runoff) affected by different land slopes, contour ridges spacing, and water harvesting structures. The results indicated that RWH increases water storage in planted area by two to three, fold depending on land slope and the contour ridges space, but with no significant differences between the applied WHT. Runoff amount increases with the increase of slope gradient (more than 5%), especially in small ridges space, which has shown the highest seasonal runoff range from 300 to 362 m^3ha^-1 at Al Mwaqar site and from 192 to 243.5 m^3ha^-1 at Al Grain site. Regression results indicated that there is high coloration between rainfall storms and runoff amount for all treatments. The best regression trend line was obtained from continuous contour ridges CT^1 and CT^2 with R^2 being 0.95 and 0.96, respectively, at Al Mwaqar site. At Al Grain site R^2 for continuous contour ranges between 0 .70 and 0.76 compared to R^2 which ranges from 0.80 to 0.93 for Vallerani intermittent trenches, due to the effect of rock fragments on the catchment surface in the continuous contour area.