This study evaluates the cause of salinization in an irrigation scheme of 100 ha supplied from a reservoir. The scheme is located in Gumselasa catchment (28 km²), Tigray region, northern Ethiopia. The catchment is underlain by limestone–shale–marl intercalations with dolerite intrusion and some recent sediments. Water balance computation, hydrochemical analyses and irrigation water quality analyses methods were used in this investigation. Surface waters (river and reservoir) and groundwater samples were collected and analyzed. The water table in the irrigated land is ranging 0.2–2 m below the ground level. The majority of groundwater in the effective watershed area and the river and dam waters are fresh and alkaline whereas in the command area the groundwater is dominantly brackish and alkaline. The main hydrochemical facies in the groundwater in the effective watershed area are Ca-Na-SO₄-HCO₃, Ca-Na- HCO₃-SO₄, and Ca-Na-Mg-SO₄-HCO₃. The river and dam waters are Mg-Na-HCO₃-SO₄ and HCO₃-SO₄-Cl types, respectively. In the command area the main hydrochemical facies in the groundwater are Ca-Na-HCO₃-SO₄ and Ca-Na-Mg-SO₄-HCO₃. Irrigation water quality analyses revealed that salinity and toxicity hazards increase from the effective watershed to the irrigated land following the direction of the water flow. The results also showed that the analyzed waters for irrigation purpose had no sodicity hazard. The major composition controlling mechanisms in the groundwater chemistry was identified as the dissolution of carbonate minerals, silicate weathering, and cation exchange. One of the impacts of the construction of the dam in the hydrologic environment of the catchment is on its groundwater potential. The dam is indirectly recharging the aquifers and enhances the groundwater potential of the area. This increment of availability of groundwater enhanced dissolution of carbonate minerals (calcite, dolomite, and gypsum), silicate weathering and cation exchange processes, which are the main causes of salinity in the irrigated land. The rising of the brackish groundwater combined with insufficient leaching contributed to secondary salinization development in the irrigated land. Installation of surface and subsurface drainage systems and planting salt tolerant (salt loving) plants are recommended to minimize the risk of salinization and salt accumulation in the soils of the irrigated land.

In this paper, a framework for best practice for incorporating climate change and adaption in Africa is presented from mainly the water resources design and management perspectives to chart systematically ways of incorporating climate change in engineering design of water development projects. This will enable engineers to address the challenges of Africa’s vulnerability to climate change and variability which has direct impacts on water availability, access and use which is the source of food and livelihood security for millions of the continent’s population. Climate change and variability is projected to affect the hydrological cycle, which, in turn, may alter the balance between water availability leading to uncertainty as to the onset of rainy seasons, dry spells, and more frequent extreme weather events, such as droughts and floods. Using case studies, the authors outline adaptation strategies to be adopted using an integrated approach in the consideration of climate change in engineering design and management of water resources systems that also link to operational aspects of water development projects. The paper also provides a set of suggested best practices in engineering design and innovative approaches to water development involving operation and management of dams and catchments in the face of climate change and variability.

HIGHLIGHTS. A combined hydraulic modelling and optimization modelling has been employed to enable the design of an efficient water distribution network, where o

Water availability is essential to Africa's socio-economic prosperity in particular for both rain-fed 20 and irrigated agriculture, municipal water supply, energy production and industry. Sustainable 21 management of water resources is key for sustaining ecosystem health, natural resources and 22 wellbeing for the local population. Yet, the African continent's water resources are currently facing 23 severe pressures from (over) exploitation of water storages, severe pollution, and infrastructural 24 challenges. In addition to pressure on water resources, it faces increased risks of hydro extremes like 25 large river floods, flash floods after local high-intense rainstorms, and droughts. 26As a continent Africa currently has over 1.4 billion people and is expecting > 3 billion people till end 27 of the century. It has a distinctly diverse climate and environment and, as elsewhere, faces problems 28 related to insufficient interaction between hydrology and society.