A risk-based groundwater modeling framework in coastal aquifers: a case study on Long Island, New York, USA
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PAPER
A risk-based groundwater modeling framework in coastal aquifers: a case study on Long Island, New York, USA Mohammad Karamouz 1 & Davood Mahmoodzadeh 1,2 & Gualbert H. P. Oude Essink 2,3 Received: 10 November 2019 / Accepted: 31 May 2020 # The Author(s) 2020
Abstract A methodology is proposed to define indices for quantifying risks under the threat of reducing in groundwater levels, the existence of saltwater intrusion (SWI), and an increasing nitrate contamination load in submarine groundwater discharge (SGD). The proposed methodology considers coastal regions under geological heterogeneity and it is tested on a groundwater system in Nassau County of Long Island, New York (USA). The numerical model is constructed with the SEAWAT code. The parameter uncertainty of this model is evaluated by coupling the Latin hypercube sampling method (as a sampling algorithm) and Monte Carlo simulation to consider the uncertainty in both hydraulic conductivity and recharge rate. The indices are presented in spatial maps that classify areas of risk to potential threats. The results show that two of the water districts have a high risk under conditions of decreasing groundwater level. Salinity occurs in the southern and southwestern parts of the Nassau County aquifer and a considerable area of high risk of SWI is identified. Furthermore, the average SGD rate with the associated fluxes of nitrate is estimated as 81.4 million m3/year (average 0.8 tons of nitrate through SGD per year), which can adversely affect the quality of life in the local coastal ecosystems. The framework developed in this study could help the water district managers to identify highrisk areas for short-term and long-term planning and is applicable to other coastal settings. Keywords Numerical modeling . Coastal aquifers . Saltwater intrusion . Quantitative indices . USA
Introduction Groundwater, as a critical source of freshwater, has a vital role in coastal regions and needs to be assessed against threats. In coastal regions, aquifers are important sources of water supply for domestic, industrial and agricultural consumption. Nowadays, high demand from the coastal groundwater
* Mohammad Karamouz [email protected] Davood Mahmoodzadeh [email protected] Gualbert H. P. Oude Essink [email protected] 1
School of Civil Engineering, University of Tehran, PO Box 14155-6619, Tehran, Iran
2
Department of Physical Geography, Utrecht University, PO Box 3584CS Utrecht, The Netherlands
3
Unit Subsurface and Groundwater Systems, Deltares, PO Box 85467, 3508, AL Utrecht, The Netherlands
systems has increased the pressure on these resources (Oude Essink et al. 2010; Ketabchi et al. 2016b; Karamouz et al. 2017, 2020; Klassen and Allen 2017). Saltwater intrusion (SWI) is a main problem in many coastal regions (Post et al. 2018). Also, submarine groundwater discharge (SGD), which is the exchange of groundwater between the land and sea, involves the associated fluxes of nutrients. Further, high water demand causes increase in the groundwater withd
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