Groundwater recharge to aquifers of the Sana'a basin, Yemen.
Doctoral thesis, University of London.
The purpose of the study is to understand quantitatively the spatial distribution of groundwater recharge in the Sana'a Basin, Yemen i.e. irrigation recharge, wadi recharge and urban recharge and to assess the impact of these components on the groundwater quality. A combination of field measurements and modelling was used to determine the irrigation return for several crops and soil types. Over the basin, the total return flows, between 20 to 40 % of the water applied, are about 30 MCM/year. A method was developed to calculate recharge through ephemeral wadi beds using an indirect approach, requiring only daily rainfall data and geomorphological observations. The technique combines a rainfall-runoff model with calculation of daily water balance for the wadi channel. The method was applied to two wadis with sufficient subsurface data to estimate groundwater recharge independently from calibration of groundwater models for the shallow aquifer. The values of infiltration calculated by groundwater flow model were in good agreement with the results of the channel water balance model. Regression analysis was used to derive a generalised relationship between recharge and wadi flows. Application of this technique allows extension of wadi recharge estimates to numerous ungauged wadis over 20 years. Wadi recharge over the Sana'a basin is erratic and varies between 129 MCM and 3 MCM with an average of 38 MCM/year. An inventory of abstraction by private wells in Sana'a city, has allowed an improved estimation of urban recharge over the last 20 years, an average of 60% of the water abstracted (76% supplied). Water chemistry indicates that the shallow aquifer within the plain and lower reaches of major wadis has been polluted. However, dilution is taking place through mixing with the deep fresh water through the boreholes. Total annual recharge varies between 143 MCM and 21 MCM with an average of 66 MCM. This represents a significant amount of the annual average abstraction of 82 MCM. Previous estimate of recharge to aquifers of the basin has been less soundly based.
|Title:||Groundwater recharge to aquifers of the Sana'a basin, Yemen.|
|Open access status:||An open access version is available from UCL Discovery|
|Additional information:||Thesis digitised by British Library EThOS. Some of the images and the original page 491 have been excluded due to third party copyright.|
|UCL classification:||UCL > School of BEAMS > Faculty of Maths and Physical Sciences > Earth Sciences|
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