Introduction: Groundwater is a vital resource for human consumption, agricultural production, and the development of water-related industries, especially in arid and semi-arid regions. Groundwater and surface water resources provide approximately 60 and 40 percent of Iran’s total water supply, respectively, where the relative water consumption in the agricultural, urban, and industrial sectors is approximately 92%, 7%, and 1%, respectively. The construction of many dams on main rivers, along with water extraction, has reduced river flows, dried them up, and damaged river-dependent ecosystems. The inflow to Tashk and Bakhtegan lakes located in Fars province has decreased due to the construction of upstream dams and the use of river water for irrigation in the past decade, leading to the drying of these lakes in 2013. The over-extraction of groundwater by ~5.4 billion cubic meters per year during the 2002-2015 period has resulted in a decrease in groundwater levels (10-100 centimeters per year) in different regions of Iran, averaging 49 centimeters per year nationwide, damaging groundwater-dependent ecosystems in some areas. For example, Parishan Lake, which is mainly the result of the inflow of groundwater from nine springs, has experienced a decrease in water depth (about 5 meters during the 1995-2008 period) due to increased groundwater extraction around the wetland. The Jahrom aquifer in Fars province has also experienced a decrease in water level of approximately 0.75 meters per year, or three aquifers Aspas, Khosrowshirin, and Kamfiruz in the north of Fars province have respectively experienced a decrease in groundwater level of approximately 0.7, 1, and 0.35 meters per year due to over-extraction. Although groundwater is a vital source for human needs and consumption, it is also vital for preserving the environment. The main point in water resources management is the neglect of environmental water needs, in other words, all the water available in a river or aquifer is only considered for human consumption. However, a physical index recently presented by Naderi (2021) takes into account environmental needs and quantifies the level of water resources management based on the concepts of available water and water supply (water extraction). The aim of this study is to quantify the level of management (LOM) of aquifers in Zanjan Province under “normal” and “sustainable” management conditions



Methods: The study area includes eight alluvial aquifers of Zanjan Province (northwestern Iran) which are located between 47010’ to 5005’ E and 35025’ to 37010’ N. About 1.6% of the province’s area has a dry climate, 76% has a semi-dry climate, 20% has a Mediterranean climate, and 2.4% has a semi-humid to humid climate. The aquifers include Tarom, Zanjan, Mahneshan, Moshampa, Sojas, Zarrin-Tappeh, Abhar, and Qeydar, which have areas of 75.5, 1146.13, 30.06, 36.1, 501.7, 495.4, 657.6, and 699.2 km2, respectively. The LOM is quantified under “normal” and “sustainable” conditions. The difference between the two LOM values stems from definitions for existing groundwater sources. Sustainable groundwater originates from the aquifer’s own region, while normal groundwater originates from both the local aquifer region and adjacent groundwaters to meet the region’s water needs.

〖LOM〗_n=(〖AGW〗_n-TWS)/〖AGW〗_n (1)

〖LOM〗_s=(〖AGW〗_s-TWS)/〖AGW〗_s (2)

〖〖AGW〗_n=R〗_n-EFR=(I_p+I_r+I_s+I_irg+I_mi+I_net )-EFR (3)

〖〖AGW〗_s=R〗_s-EFR=(I_p+I_r+I_s+I_irg+I_mi )-EFR (4)

In the above relations, subscripts n and s represent normal and sustainable conditions, respectively. AGW is available groundwater, TWS total water supply, R the recharge of groundwater, EFR the environmental flow requirement, infiltration from precipitation (Ip), groundwater recharge from the river (Ir), groundwater recharge from runoff (Is), groundwater recharge due to irrigation return flow (Iirg) and municipal-industrial (Imi) water use, and net groundwater recharge from adjacent groundwaters (Inet).



Results: Alluvial aquifers of Tarom, Zanjan, Mahneshan, Moshampa, Sojas, Zarrinabad, Abhar, and Qeydar have experienced groundwater storage anomalies of 2.57, -25.61, 3.83, 0.82, -6.46, -9.52, -45.80, and -19.55 million cubic meters per year, respectively. Only the aquifers of Tarom, Mahneshan, and Moshampa have positive changes in storage volume. Results show that in the Mahneshan aquifer, normal management was positive (3 percent) but sustainable management was negative and close to zero (-0.1 percent). Therefore, the type of management is “pseudo-sustainable”. In the Moshampa aquifer, normal management was positive (2 percent) but sustainable management was negative (-9.7 percent). Therefore, the type of management is “pseudo-sustainable”. In the Tarom aquifer, normal management was positive (6.5 percent) but sustainable management was negative (-0.38 percent). Therefore, the type of management is “pseudo-sustainable”. In other aquifers, both normal and sustainable management were negative and indicative of the “mismanagement” class, so that normal and sustainable management in the Zanjan aquifer were respectively -9 and -41 percent, in the Sojas aquifer were -8.9 and -17.7 percent, in the Zarrinabad aquifer were -18.5 and -68 percent, in the Abhar aquifer were -30 and -106 percent, and in the Qeydar aquifer were -14 and -106 percent. Therefore, it is necessary to improve the status of water resource management, using various solutions such as wastewater treatment, education and increasing public awareness in optimal water consumption, reducing the cultivated area, increasing irrigation efficiency, and cultivating crops with less water demand to reduce groundwater abstraction in Zanjan Province.