Kızılırmak river basin hydrogeological investigation

Overview

In all groundwater systems, the total amount of water entering, leaving, and being stored must be conserved. The EU’s river management plans requires Member States to use their river basin management plans and programmes of measures to protect and, where necessary, restore water bodies to achieve positive results, and prevent deterioration.

Our study of the Kızılırmak river basin tackled complex hydrogeological challenges through comprehensive Geo-data acquisition and integration, and precise conceptual modelling. By subdividing the basin into 27 manageable units and establishing an extensive monitoring network, we provided the client with reliable groundwater budget calculations (the flow in and out of the system) and sustainable management strategies, setting a new standard for large river basin hydrogeological investigations in Turkey.

Challenges

Data limitations

Inadequate or inconsistent data on recharge rates, discharge rates, and subsurface flow characteristics can lead to significant uncertainties. The limited number of meteorological stations able to provide long-term measurements made accurate hydrological budget calculations more complicated.

Complex hydrogeological systems

Diverse geological formations and structural elements contribute to the complexity of this hydrogeological system, making it harder to understand the interactions between ground- and surface water.

Location and time variations

This dynamic hydrogeological system varies across both time and location, with seasonal and long-term changes in climate and land use causing fluctuations in groundwater levels and recharge rates. Therefore, regular and long-term Geo-data measurements are essential for accurate assessment.

Human impact

High levels of groundwater extraction, land use changes, and contamination significantly alter natural groundwater flow patterns and budgets, leading to deficits and increased pressure on water resources. Additionally, water structures like dams, ponds, and canals, which alter natural flow directions and surface water/groundwater interactions, are crucial in groundwater budget calculations. Obtaining accurate operational volumes and data on diversions was challenging but essential for quantifying post-operational groundwater budgets.

Pressure from agricultural and industrial activities

Agricultural activities, livestock farming, and industrial use heavily impact groundwater quality and quantity. Therefore, detailed pressure, impact and risk analyses are needed to manage and mitigate the effects from these activities.

Solutions

Geo-data acquisition

We carried out thorough Geo-data acquisition and analysis, covering all aspects of groundwater dynamics. Our Geo-data included identification of almost 24,000 wells and over 600 springs; detailed groundwater level measurements and spring discharge measurements at approximately 1000 locations during wet and dry periods; and groundwater quality and isotope sampling at almost 800 locations. We also conducted geophysical studies, such as vertical electrical sounding, at nearly 600 critical locations to understand the depth of alluvium. Additionally, we reviewed huge amounts of historical Geo-data and integrated it with new Geo-data obtained from meteorological, hydrological, and demographic sources to provide a foundation for accurate groundwater budget calculations.

Geological mapping

To identify the water-bearing units of the basin, the geology of the entire basin was delineated at a 1:25,000 scale. During this study, we identified 468 different types of geological formations and examined their layers and structure, which are important for understanding how groundwater moves through the area. We then assessed the water-related properties of the rock layers and their ability to store water to help determine the best places to find and extract groundwater.

Multidisciplinary approach

Once we had our field data, we integrated the outcomes of all the geological, geophysical, hydrological, hydrogeological, and geochemical studies to provide a holistic understanding of the basin’s hydrogeology.

Subdivision into manageable units

At over 82,000 km², the Kızılırmak basin covers a large area, so we divided it into 27 hydrological sub-basins and 82 distinct groundwater systems. This subdivision allowed for detailed and precise management, facilitating a better understanding and control of groundwater resources.

Geo-data integration

We integrated Geo-data sources, including geological maps, geophysical measurements, hydrogeological data and long-term monitoring results, to ensure robust and accurate analysis, and to enhance the reliability of the groundwater budget calculations.

Hydrological conceptual models

Conceptual models reflecting both natural and post-construction conditions were developed. These models provided insights into the impacts of human activities on groundwater systems, helping in the formulation of effective management strategies.

Monitoring network

At the end of the study, based on the results obtained from groundwater budget calculations and pressure and risk assessments, we established an extensive network for future monitoring. This network will enable continuous and detailed observation of groundwater levels and quality, and over time it will help improve the accuracy of hydrogeological assessments. Regular and long-term Geo-data measurements at multiple locations will ensure that hydrogeological models are continuously updated and refined, allowing management strategies to be adjusted accordingly.

Impact

Our comprehensive hydrogeological solutions provided DSi with a detailed understanding of the Kızılırmak river basin’s groundwater dynamics that will help in locating reliable water sources for drinking, irrigation, and other needs.

The subdivision into manageable units, coupled with Geo-data integration and detailed conceptual models, enabled reliable groundwater budget calculations and development of sustainable management strategies.

Meanwhile, our monitoring network will provide more accurate assessments in the future and allow continuous improvement of these models through an iterative approach.

Our innovative approach took this study above and beyond conventional hydrogeological investigations in Turkey and set a new benchmark for groundwater management in large river basins.