The Possibility of Managed Aquifer Recharge (MAR) for Normal Functioning of the Public Water-Supply of Zagreb, Croatia

Abstract

With its quantities of groundwater, the Zagreb aquifer is an irreplaceable water-supply resource that forms the basis of the water-supply of Zagreb, the capital and largest city of the Republic of Croatia. The depth of the Zagreb aquifer system is about 100 m at the deepest part, and the two main aquifers of the aquifer system can be separated vertically by low-permeable clay deposits. In the area of the Zagreb aquifer, there are several active and reserve public water-supply sites, the largest of which are Mala Mlaka and Petruševec. The groundwater level of the Zagreb aquifer is directly related to the water levels of the Sava River, so any erosive change in the Sava riverbed decreases the groundwater levels in the aquifer. In the last 50 years, the groundwater levels in the Zagreb aquifer have decreased significantly, being most pronounced in the area of the Mala Mlaka water-supply site. This has affected the normal functioning of the public water-supply because the suction baskets of the pumps in the dug wells at the Mala Mlaka water-supply site occasionally remain partially or completely in the unsaturated aquifer zone during low groundwater levels, which reduces capacity or prevents pumping from these water-supply facilities. Immediately next to the Mala Mlaka water-supply site is the Sava-Odra Canal, which was built to protect Zagreb from flooding and into which the Sava River flows when its flow rate exceeds 2350 m3/s. This reduces the flow rate of the Sava River near Zagreb and the possibility of flooding urban areas. To prevent problems with groundwater levels at the Mala Mlaka water-supply facilities and to enable normal water-supply, even in extremely dry periods, several variants of managed aquifer recharge (MAR) are proposed here. In order to determine the optimal solution for MAR and to enable the normal functioning of one of the main sites of water-supply in the Zagreb water-supply system. Groundwater flow for the period of 2006 to 2010 was simulated for six different variants of MAR. One assumes a constant potential in the Sava-Odra Canal, three are related to recharge from the Sava-Odra Canal with different backwater levels in the infiltration facility (elevations of 114, 114.5, and 115 m a.s.l.), and two with three absorption wells upstream of the Mala Mlaka water pumping station (injection of 300 L/s each and 500 L/s each). The most favorable method to recharge artificially the Zagreb aquifer near the Mala Mlaka pumping station is achieved with an infiltration facility using an elevation of 115 m a.s.l. The use of such a facility will enable the smooth operation of the water pumping station and the possibility of increasing the pumping quantities at the Mala Mlaka water pumping station for the future development of the area.

Impact of Hydrological Conditions on the Isotopic Composition of the Sava River in the Area of the Zagreb Aquifer

“…Furthermore, the results show much more deviation in the isotopic signature at the DM bridge. Together with the results of in-situ measurements and previous research, where it was shown that the connection between Sava River and Zagreb aquifer system is not uniform [6,33,42,43], these results indicate that mixing between surface water and groundwater is more pronounced in the downstream part of the Zagreb aquifer. Greater aquifer depth in the downstream part, as well as the existence of TE-TO Zagreb, generates slower velocities and enables more time for infiltration of the Sava River into the Zagreb aquifer, which is consistent with the results of the previous research [6].…”

“…Although it has been found that the main boundary condition related to the recharge of the Zagreb aquifer is the Sava River, which generates recharge from 67.5% up to 83.74% depending on the area which is evaluated [6], no research was focused on the evaluation of the Sava River isotopic pattern at the entrance of the Zagreb aquifer, i.e., the inflow area, and its isotopic difference with respect to the exit of the aquifer, i.e., the outflow area. The latest hydrogeological research confirmed that the hydraulic connection between the Sava River and groundwater is complicated and not uniform [33].…”

Water Recharges Suitability in Kabul Aquifer System within the Upper Indus Basin

“…Therefore, improved groundwater management is needed to ensure an adequate water supply to the expanding city. One of the most appropriate ways to enhance the condition of the aquifer is to use the managing aquifer recharge (MAR) technique, which is widely used for different regions [13][14][15][16][17][18]. Regional recharge studies in the Kabul aquifer have been limited to traditional approaches to groundwater and recharge exploration which only utilized drilling and geophysical methods in some small areas sporadically due to the expensive field work investigations and the regional complexity with confrontations and wars [19].…”