Rainwater harvesting for supplemental irrigation under tropical inland valley swamp conditions

• Published in: Irrigation and drainage 2020-12, Vol.69 (5), p.1095-1105
• Main Authors: Blango, Mohamed M., Cooke, Richard A.C., Moiwo, Juana P., Sawyerr, Patrick A., Kangoma, Emmanuel
• Format: Article
• Language: English
• Subjects: Agricultural management; Agricultural production; Atmospheric precipitations; Barrages; condition tropicale; Crop growth; Crop yield; Cultivation; Dry season; dry season irrigation; Earth dams; Energy; Evaporation; Food; Food security; Gravity; groundwater recharge; Growth conditions; Harvest; Harvesting; inland valley swamp; Irrigation; irrigation en saison sèche; Irrigation water; marais de la vallée intérieure; Precipitation; Rain; Rain water; Rainfall; rainwater harvesting; Rainy season; recharge des eaux souterraines; Rice; récupération des eaux pluviales; Seepage; Solar radiation; Supplemental irrigation; Swamps; Tropical climate; tropical conditions; Valleys; Water harvesting; Water management; Water supply; Wet season
• ISSN: 1531-0353; 1531-0361
• DOI: 10.1002/ird.2496

Agricultural water management, if well implemented, could increase water supply and food security across the developing world. Simple earth dams or reservoirs are sufficient in this case for gravity‐driven irrigation to support agricultural production throughout the year. This is critical for regions with little energy and limited farm irrigation, but abundant precipitation. In Sierra Leone, energy especially as electricity is hardly available and farming is over 80% rainfed. This critical shortfall has limited crop cultivation to almost entirely the wet season in the country. Here, we developed an earthen micro‐dam and analysed its potential for rainwater harvesting and supplemental irrigation in the dry season in an inland valley swamp at Njala University. For the 2014–2017 dry season cropping period, average daily evaporation, seepage and irrigation from the 4.2 × 104 m3 dam were respectively 2.84, 0.51 and 7.76 mm. Thus, with 124 mm (79.5 m3) dam water irrigation and 409 mm precipitation in the dry season, grain yield increased by 67% (1430 kg ha¯¹) over that (2130 kg ha¯¹). This implies that the additional rice harvest in the dry season in excess of the rice harvest in the wet season was 67%. In other words, the harvest in the dry season was 3560 kg ha¯¹. The higher harvest in the dry season was attributed to the more favourable crop growth conditions (including solar radiation and supplemental irrigation) in the dry season than in the wet season. The additional harvest in the dry season could be significant in closing food security gaps, especially in tropical Africa where rainfall is plenty and energy availability limited. Résumé La gestion de l'eau agricole, si elle est bien mise en œuvre, pourrait accroître l'approvisionnement en eau et la sécurité alimentaire dans le monde en développement. De simples barrages ou réservoirs en terre suffisent dans ce cas à une irrigation par gravité pour soutenir la production agricole tout au long de l'année. Ceci est essentiel pour les régions avec peu d'énergie et une irrigation agricole limitée, mais des précipitations abondantes. En Sierra Leone, l'énergie surtout l'électricité est peu disponible et l'agriculture est pluviale à plus de 80%. Ce déficit critique a limité la culture des cultures à presque entièrement la saison des pluies dans le pays. Ici, nous avons développé un micro‐barrage en terre et analysé son potentiel de collecte des eaux de pluie et d'irrigation supplémentaire pendant la saison sèche