Az unprecedented low water level of the Danube in Budapest has revealed more than just historical artifacts and wartime remnants. Beyond bridge foundations and explosives, numerous previously hidden thermal springs have become visible in the riverbed. This extraordinary situation underscores the intricate connection between surface and subsurface water systems, prompting experts to emphasize the critical need for responsible water management.
During recent research, Dr. Erőss Anita, an ELTE hydrogeologist, and her team discovered significantly more thermal springs in the dry or shallow sections of the Danube bed than the three previously documented in the 1920s. These 42-43 Celsius-fokos források, bubbling up between the Szabadság híd and Erzsébet híd, became observable because the river's drastically lowered level could no longer suppress their flow. The unexpected presence of thermal water directly in the river highlights a fundamental hydrological principle: surface and subsurface waters are not isolated entities but are in constant interaction.
Historically, only three thermal water upwellings were officially recorded in the Budapest section of the Danube during the 1920s. Under normal circumstances, the river's volume conceals these natural phenomena. However, the current extreme drought conditions and record-low water levels have made these areas accessible for renewed scientific investigation. This visibility offers a unique opportunity to study the dynamics of these geothermal outflows and their interaction with the river system.
The phenomenon mirrors situations seen elsewhere, such as with Lake Velence, where a significant drop in subsurface water levels due to drought directly impacts the lake's water volume. The lake faces severe challenges when the surrounding groundwater level falls below its bed, illustrating the direct consequences of inadequate subsurface water management.
Dr. Erőss Anita emphasizes the critical importance of how Hungary manages its subsurface water resources, which are vital for various sectors. A substantial portion of the nation's drinking water originates from these underground reserves, and they are extensively utilized by industry and agriculture. While household consumption, including garden watering and pool filling, represents a smaller proportion, every form of water usage contributes to the overall demand, especially during periods of scarcity.
Despite Hungary's advantageous geological conditions, with sedimentary basins efficiently storing water, these resources are not limitless. The key challenge lies in maintaining a sustainable water balance, ensuring that precipitation replenishes the extracted quantities. The hydrogeologist cautions against a generalized approach to water extraction, stressing that the feasibility of further withdrawal depends entirely on the specific location, the depth and type of aquifer, and its natural replenishment rate.
The increasing frequency of intense, short-duration rainfall events due to climate change poses a significant challenge, as the ground often cannot absorb such large volumes of water. This leads to rapid runoff into drainage systems, rivers, and ultimately out of the region. Erőss Anita advocates for a stronger focus on effective rainwater management, proposing strategies to retain precipitation locally and systematically return it to subsurface water systems. Such methods could include targeted infiltration, which would help replenish both shallow and deep aquifers, a practice gaining traction globally.
Regarding thermal water utilization, the expert suggests prioritizing its heat energy potential through closed-loop systems. This approach would involve using the thermal water for heating or other purposes and then reinjecting it underground, thereby preserving the quantity of subsurface water resources. She strongly opposes discharging used, often saline, thermal water into freshwater rivers or streams, as this introduces alien substances harmful to local ecosystems.
The overarching goal should be the long-term preservation of both the quantity and quality of subsurface waters, ensuring their diverse utility and their crucial role in naturally sustaining surface waters, particularly during dry periods. Understanding the interconnectedness of surface and subsurface water is crucial for recognizing how human activities impact these complex systems. The low Danube water level serves as a visible reminder of these hidden processes, highlighting the need for both large-scale and individual efforts in sustainable water stewardship.
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