Karasu Karst Kaynağı (Bilecik) Hidrojeolojik İncelenmesi

Abstract

In Turkey, there are many springs used for drinking and domestic water one of them is Karasu Karst Spring. The Karasu Karstic Spring is located in Bozalan village of Bozüyük district, Bilecik province in the western part of the Central Sakarya Basin. The Karasu Karst Spring is a karstic spring discharging from Jurassic-Cretaceous aged marbles with an average flow rate of 1.842 m³/s. According to the Protection Announcement of the Karasu Spring in Bilecik-Bozüyük District published by the General Directorate of State Hydraulic Works (DSI) Geotechnical Services and Groundwater Department, the Karasu Karst Spring is used for drinking, domestic, and industrial water primarily for Bilecik province and Osmaneli, Pazaryeri, Söğüt, and Bozüyük districts and some other settlements. Therefore, the protection of this spring is of great importance. In this context, the Karasu Karst Spring was placed under protection in 2012 in accordance with the "Regulation on the Protection of Groundwater Against Pollution and Deterioration" and the "Communiqué on the Determination of Protection Zones of Aquifers and Springs Supplying Drinking Water."

Karst springs are affected more quickly by natural (e.g., precipitation, temperature) and anthropogenic (e.g., human-induced pollution) activities accuring in their recharge are connected to other groundwater sources, and their response to this impact is also more rapid. In this respect, ensuring the sustainability of the Karasu Karst Spring in terms of both quantity and quality is only possible by managing the spring on the basis of a properly designed hydrogeological conceptual model. Within the scope of this thesis, the geological and hydrogeological structure of the spring and its associated hydrogeological system have been identified through maps and cross-sections, geomorphological studies have been conducted, the recharge, storage, and discharge processes of the spring have been determined through existing spring flow data and drawdown analyses, and the origin and recharge mechanism of the spring have been identified through major ion and isotope analyses. It has been concluded that 96.88% of the discharge of Karasu Karst Spring is derived from infiltration within the recharge area of the Geyiktepe Formation, while 3.11% comes from the surface drainage area located upstream of the spring’s discharge point. Hydrogeochemical and isotope analyses indicate that calcium (Ca) and bicarbonate (HCO3) are the dominant ions in all samples, and that diffuse flow occurs within the aquifer. The residence time of water discharging at the main spring outlet was calculated to be approximately 13.2 to 18.3 years during dry periods and 6.3 to 11.4 years during wet periods. Additionally, a vulnerability map to pollution of the aquifer associated with the spring was created using the EPIK method, showing that 3.3% of the study area falls into the S1 (very high) vulnerability class, 39.7% into the S2 (high) class, and 57% into the S3 (moderate) class. Furthermore, in assessments of the impact of climate change on the spring’s discharge, under the RCP8.5 scenario, it is projected that the discharge rate of Karasu Karst Spring will decrease by 17.79% (0.312 m³/s) between 2041 and 2070.

This thesis aims to contribute to the achievement of the 6th Goal, “Clean Water and Sanitation,” and the 13th Goal, “Climate Action,” as outlined by the United Nations Sustainable Development Goals, which seek to ensure the availability and sustainable management of water and sanitation for all and to take urgent action to combat climate change and its impacts. Furthermore, within the scope of the thesis, information that will form the basis for the sustainable management planning of the spring for the General Directorate of State Hydraulic Works and related municipalities.