Application of modified two-point hedging policy in groundwater resources planning in the Kashan Plain Aquifer
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Abstract: Effective management of water resources, especially groundwater, is crucial and requires a precise understanding of aquifer characteristics, imposed stresses, and the groundwater balance. Simulation-optimization models plays a vital role in guiding planners toword sustainable long-term aquifer exploitation. This study simulated monthly water table variations in the Kashan Plain over a ten-year period from 2008 to 2019 across 125 stress periods using the GMS model. The model was calibrated for both steady-state and transient conditions for the 2008–2016 period and validated for the 2016–2019 period. Results indicated a 4.4 m decline in groundwater levels over the 10-year study period. Given the plain's location in a arid climatic zone with limited effective precipitation for aquifer recharge, the study focused on groundwater extraction management. A modified two-point hedging policy was employed as a solution to mitigate critical groundwater depletion, reducing the annual drawdown rate from 0.44 m to 0.31 m and conserving 255 million cubic meters (mcm) of water annually. Although this approach slightly decreased reliability (i.e. the number of months meeting full water demands), it effectively minimized the risk of severe droughts and irreparable damages. This policy offers managers a dynamical and intelligent tool for regulating groundwater extraction, balancing aquifer sustainability with agricultural and urban water requirements.
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Figure 4. Types of hedging rule (Shourian and Jamshidi. 2022)
Table 1. The number and discharge of groundwater resources (mcm).
Alluvial aquifer Total range Heights Plain Resource Discharge Number Discharge Number Discharge Number Discharge Number 239.42 961 267.36 1958 25.86 987 241.5 971 Well 0 0 27.90 268 27.90 268 0 0 Spring 6.46 33 97.37 540 88 504 250.9 36 qanat Table 2. Water consumption and its resources by plain and heights areas (mcm).
Surface water and spring Groundwater (well and qanat) Total agriculture Industry Urban Agriculture Industry Urban 261.13 1.85 0 8.50 268.29 5.37 27.11 Plain 88.50 26.61 0.21 0.51 51.11 1.16 8.90 Heights Table 3. Parameter statistics obtained from transient calibration
Standard deviation Mean Min Max Parameter 0.081 0.072 0.0026 0.45 Sy 29.5 15.73 0.003 139.5 HK (m/d) Table 4. Error evaluation criteria for the simulation model.
ME (m) RMSE (m) bR2 Stage 0.64 0.34 0.95 Calibration 0.82 0.41 0.89 Validation Table 5. Results of the three groundwater extraction scenarios
15% decrease in extraction 15% increase in extraction Current extraction trend 887.6 887.6 887.6 Water table of the first month (2008) 880.6 875.78 877/81 Water table of the last month (2029) −6.9 −11.9 −9.8 Groundwater drop Table 6. Decision variables of the modified two-point Hedging
EWA(MCM) SWA(MCM) HF Month 207.65 21.2 0.36 October 180.02 13.06 0.22 November 134.89 11.32 0.35 December 101.35 7.89 0.22 January 95.65 10.94 0.26 February 104.87 10.97 0.35 March 115.36 10.69 0.38 April 139.12 14.08 0.48 May 150.23 24.56 0.51 June 208.84 30.21 0.55 July 211.54 33.47 0.64 August 133.62 25.76 0.49 September Table 7. Performance criteria for supply-demand management using the modified two-point hedging policy
Sustainability Vulnerability Resilience Reliability Selected Optimal solution MSI Drawdown 51 62 46.06 77.46 3.35 0.31 Table 8. Comparison between extraction scenarios
MTPHP(Modify Two Point Hedging Policy) 15% decrease extraction Current trend extraction Extraction scenario 0/31 0/35 0/45 Groundwater depletion (m/a) -
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