Technical note: Introduction of a superconducting gravimeter as novel hydrological sensor for the Alpine research catchment Zugspitze

GFZ (German Research Centre for Geosciences) set up the Zugspitze Geodynamic Observatory Germany with a worldwide unique installation of a superconducting gravimeter at the summit of Mount Zugspitze on top of the Partnach spring catchment. This high alpine catchment is well instrumented, acts as natural lysimeter and has significant importance for water supply to its forelands, with a large mean annual precipitation of 2080 mm and a long seasonal snow cover period of 9 months, while showing a high sensitivity to climate change. However, regarding the majority of alpine regions worldwide, there is only limited knowledge on temporal water storage variations due to sparsely distributed hydrological and meteorological sensors and the large variability and complexity of signals in alpine terrain. This underlines the importance of well-equipped areas such as Mount Zugspitze serving as natural test laboratories for improved monitoring, understanding and prediction of alpine hydrological processes. The observatory superconducting gravimeter, OSG 052, supplements the existing sensor network as a novel hydrological sensor system for the direct observation of the integral gravity effect of total water storage variations in the alpine research catchment at Zugspitze. Besides the experimental set-up and the available data sets, the gravimetric methods and gravity residuals are presented based on the first 27 months of observations from 29 December 2018 to 31 March 2021. The snowpack is identified as being a primary contributor to seasonal water storage variations and, thus, to the gravity residuals with a signal range of up to 750 nm s−2 corresponding to 1957 mm snow water equivalent measured with a snow scale at an altitude of 2420 m at the end of May 2019. Hydro-gravimetric sensitivity analysis reveal a snow–gravimetric footprint of up to 4 km distance around the gravimeter, with a dominant gravity contribution from the snowpack in the Partnach spring catchment. This shows that the hydro-gravimetric approach delivers representative integral insights into the water balance of this high alpine site.

Water balance component analysis of a spring catchment of western Nepal

Springs in the mountains and hills are getting affected by both climatic and non-climatic changes. Hydrologic models are used to simulate the response of spring systems to the changes; however, only a limited number of studies using the hydrologic modeling approach have been accomplished on studying springs and spring-dominated watersheds in Nepal. This research aimed at understanding changing hydrological processes through hydrologic modeling in a spring catchment. A micro-catchment named 'Sikharpur' of West Seti watershed of Nepal was selected to get insights into the process influencing the spring system. The RRAWFLOW models with gamma distribution and time variant IRFs were calibrated and validated for the catchment to get the best fit model. The discharge was simulated according to the future projected climate scenarios. Then, a water balance was assessed for the micro-catchment. The results showed that understanding of likely response of hydrologic variables to potential future climate scenarios is critical for water resource management. It was estimated that the spring discharge would be decreased by more than 40 percentage after 50 years mainly due to the increase in evapo-transpiration (91.47% of the precipitation). Evapo-transpiration was found as a major hydrologic process impacting upon water balance in the spring catchment; therefore, its management for better spring resource conservation is recommended by considering high evapo-transpiration months, water deficient period and crop factor. The change in the storage was observed to be 51.78%; so, detail isotopic analysis and long-term monitoring of water balance is required for further characterization of water balance components.

The potency of water availability and its use by the community around the Mount Merbabu National Park

Water is one of the basic needs for every living thing, including humans. This study aims to determine the availability of water in the two springs, the utilization of water by the community around MMNP, the vegetation characteristics of the spring catchment areas, and the Water Use Index (WUI). Data of water availability was taken using the volumetric method. Water utilization by the community is collected by doing the interviews with the respondents. The vegetation characteristics is analyzed based on the vegetation density by using the NDVI method. Meanwhile, the Water Use Index (WUI) is obtained from a comparison between water demand and water supply. The results showed that the water debit available in the Tuk Simuncar and Tuk sipendok was 23.22 liters/second and 31.20 liters/second which were classified as class IV. The area of Tuk simuncar is dominated by high density vegetation (75 Ha), while Tuk Sipendok is dominated by moderate density vegetation (102.28 Ha). The community around MMNP uses 211 liters of water for household needs, 59 liters for livestock, and 10 liters for agriculture. The Water Use Index (WUA) of the two springs has a value of 0.3 which is included in the low level.

A Steady-State Model to Simulate Groundwater Flow in Unconfined Aquifer

The hydraulic and hydrogeological features of the Caposele aquifer have been investigated by using a numerical groundwater flow model. In particular, groundwater flow simulations were performed for a multilayered, unconfined aquifer in steady-state conditions for different thicknesses of the aquifer’s saturated zone. The Caposele groundwater model was carried out starting from a generic model drained by a unique spring outlet in accordance with the geo-hydrological features of the study area. The conceptual model was built considering hydrogeological features of spring catchment, and was then implemented with the MODFLOW numerical code. A combined 2D-3D approach was adopted, and the model was calibrated on borehole data available for the time period 2012–2019. Different thicknesses of the aquifer were set, and a reliable relationship was found between the hydraulic head, saturated zone and hydraulic conductivity of the aquifer. Using the MODPATH package, the mean travel time (Darcian) of groundwater was computed for five different scenarios, corresponding to the model’s depths; the analysis that was performed shows that the travel time is higher for a greater and lower for a smaller thickness of the aquifer’s saturated zone, respectively. The Caposele aquifer model was zoned in different sectors, named flow pipe areas, that play different roles in groundwater recharge-discharge processes. A vector analysis was also carried out in order to highlight the ascendant flow near the spring zone.

An Intermittent Karst River: The Case of the Čikola River (Dinaric Karst, Croatia)

Intermittent and ephemeral streams (IRES) are responsible for transporting about half of the water on Earth’s surface. Their hydrological behavior is different in various landscapes. IRES are found more often in karst terrains than in any other regions, as a consequence of strong and direct interaction between groundwater and surface water. This paper presents a hydrogeological and hydrological analysis of the intermittent Čikola River and Spring catchment, which is located in deeply karstified and developed parts of the Dinaric karst in Croatia. Hydrological calculations determined that the catchment area covers approximately 300 km2 and very probably changes in accordance with rapid variations in groundwater level. The karst spring of the Čikola River is a cave, extracted for a public water supply with four drilled extraction wells. The results of the interrelated hydrological and hydrogeological analysis show interesting phenomena from an intermittent karst spring (cave) and its catchment, flowing downstream through a karst polje with several smaller confluences, then entering a karst canyon (where the river sinks during certain periods), and ending in an estuary before contributing to the larger Krka River. The research presented was based on water balance calculations, climatic and hydrological time series analyses, spring pumping tests, and thorough hydrogeological interpretation.

Utilizing Precipitation and Spring Discharge Data to Identify Groundwater Quick Flow Belts in a Karst Spring Catchment

In karst terrains, fractures and conduits often occur in clusters, forming groundwater quick flow belts, which are the major passages of groundwater and solute transport. We propose a cost-effective method that utilizes precipitation and spring discharge data to identify groundwater quick flow belts by the multitaper method (MTM). In this paper, hydrological processes were regarded as the transformation of precipitation signals to spring discharge signals in a karst spring catchment. During the processes, karst aquifers played the role of signal filters. Only those signals with high energy could penetrate through aquifers and reflect in the spring discharge, while other weak signals were filtered out or altered by aquifers. Hence, MTM was applied to detect and reconstruct the signals that penetrate through aquifers. Subsequently, by analyzing the reconstructed signals of precipitation with those of spring discharge, we acquired the hydraulic response time and identified the quick flow belts. Finally, the methods were applied to the Niangziguan Spring (NS) catchment, China. Results showed that the hydraulic response time of the spring discharge to precipitation was 3 months at Pingding County; 4 months at Yuxian County, Yangquan City, Xiyang County, and Heshun County; and 27 months at Shouyang County and Zouquan County. These results suggested that Pingding County is located at a groundwater quick flow belt, which is a major passage of groundwater and contaminants, in the NS catchment. This is important since Pingding County is not only the key development area of karst groundwater but also the key conservation area for sustainable development of karst groundwater resources in NS catchment.

Effective water quantity of multi-source water recharging aquifers in Yufuhe River based on groundwater and surface water semi-coupled modelling

With rapid urbanisation, a karst water recharge area of the Jinan spring catchment was damaged. Thus, managed aquifer recharge projects were built in the western Jinan spring catchment to protect the water supply of the spring. Yufuhe River was selected as the study area to compute the effective recharge rate into karst aquifers. This strong seepage zone has a large gradient and undergoes a specific hydrogeological condition in which two strata of a gravel layer and limestone change to three strata of gravel, impermeable clay shale and limestone at the open window of the karst aquifers. A hydraulic model called HEC-RAS was applied to simulate the river stage, and a numerical groundwater model called HYDRUS-3D was adopted to simulate the groundwater mound dynamics and estimate river flow seepage into the aquifers. The effective recharge rates are 64.9%, 65.2% and 68.1% when the buried depths of groundwater are 40, 30 and 25 m. An analysis of the electric conductivity, water table, temperature and water volume data found an effective recharge rate of 68.3%. Results of field monitoring confirmed the accuracy of the numerical simulation and showed that most of the recharged water in the study reach can be effectively recharged into the karst aquifers.