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Recharge Assessment as Influenced by Floodwater Spreading in a Dry Region
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نویسندگان
استادیار بخش حفاظت خاک و آبخیزداری، مرکز تحقیقات و آموزش کشاورزی و منابع طبیعی فارس
چکیده
Water scarcity due to climate change and a growing water demand in different consumption sectors is a major environmental crisis that drives arable lands to the state of degradation, especially in dry regions. Artificial recharge of groundwater (ARG) through floodwater spreading (FWS) which is a potential measure for reversing this emerging trend is investigated in this research. The overall objective of this dissertation is to evaluate a floodwater spreading system that was installed in 1981 at the Gareh Bygone Plain, southern Iran for recharging the groundwater table. The main research objectives are i) to assess the recharge of the groundwater by the floodwater spreading system using a combination of two types of saturated zone methods, water table fluctuation (WTF) and water budget, and ii) to assess the recharge by the same system using a vadose modelling approach based on soil water content measured over the vadose zone using probes that were particularly calibrated for the stony layers of interest.
In a first ‘saturated zone’ approach, the recharge was calculated at 7.94 Mm3, which was a consequence of both artificial recharge and natural replenishment. The artificial recharge data in the same period during the flooding events from 28 January to 2 February 2011 show a total volume of 6.92 Mm3 of retained flood water in the FWS systems. Artificial recharge from these events, which ponded an average depth of 0.34 m on the system surface, was calculated as 0.24 cm. The artificial recharge was calculated by the two methods (flow data and water budget, respectively) as 4.84 and 4.46 therefore, 56 to 61% of the recharge could be assigned to the impact of the FWS systems for this hydrological year.
In a second ‘unsaturated zone’ approach, recharge of the groundwater table was evaluated by measuring and modelling water content within the vadose zone inside the FWS systems. Calculations using the soil water balance and Hydrus1D methods, indicated that out the 51.8 cm of rainfall and ponded floodwater added to the site during the 16 January to 23 August 2011 period, 29.6 cm of cumulative flux (recharge) occurred, showing an efficiency of 57%. To recapitulate briefly, it might be concluded that, notwithstanding the decline in groundwater table observed in recent decades in the Gareh Bygone Plain, the FWS systems that was installed there in 1981 seems to be effective in recharging the groundwater table. Two independent approaches suggest that 57 to 61% of rainfall effectively flows to the groundwater table.
In a first ‘saturated zone’ approach, the recharge was calculated at 7.94 Mm3, which was a consequence of both artificial recharge and natural replenishment. The artificial recharge data in the same period during the flooding events from 28 January to 2 February 2011 show a total volume of 6.92 Mm3 of retained flood water in the FWS systems. Artificial recharge from these events, which ponded an average depth of 0.34 m on the system surface, was calculated as 0.24 cm. The artificial recharge was calculated by the two methods (flow data and water budget, respectively) as 4.84 and 4.46 therefore, 56 to 61% of the recharge could be assigned to the impact of the FWS systems for this hydrological year.
In a second ‘unsaturated zone’ approach, recharge of the groundwater table was evaluated by measuring and modelling water content within the vadose zone inside the FWS systems. Calculations using the soil water balance and Hydrus1D methods, indicated that out the 51.8 cm of rainfall and ponded floodwater added to the site during the 16 January to 23 August 2011 period, 29.6 cm of cumulative flux (recharge) occurred, showing an efficiency of 57%. To recapitulate briefly, it might be concluded that, notwithstanding the decline in groundwater table observed in recent decades in the Gareh Bygone Plain, the FWS systems that was installed there in 1981 seems to be effective in recharging the groundwater table. Two independent approaches suggest that 57 to 61% of rainfall effectively flows to the groundwater table.
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