Identifying flow regime in the aquifer of fractured rock system in Germi Chai Basin,Iran

Considering the importance of fractured rock aquifers in the hydrogeologic process,this research aimed to analyze the flow regime,internal degree of karstification,and estimate storage volume in fractured rock aquifers of the Germi Chai Basin in northwest Iran,which is attributed to its active tectonics,erosion,and the lithological diversity.Given the geological setting,the hypothesis is that this basin is characterized by a high degree of karstification and diffuse or intermediate flow regime leading to variation in discharge flow rate.The hydrodynamic and hadrochemical analysis was conducted on 9 well distributed springs across the basin from 2019 to 2020.The maximum flow rate in most of the springs appeared in the early wet season despite their different levels of fluctuations on the monthly discharge time series.Analyzing the spring recession curve form revealed an aquifer containing multiple micro-regimes withαrecession coefficients and a degree of karstification ranging between 0.001 to 0.06 and 0.55 to 2.61,respectively.These findings indicated a dominant diffuse and intermediate flow system resulting from the development of a high density of fractures in this area.The electrical conductivity of the spring changes inversely proportional to the change in flow discharge,indicating the reasonable hydrological response of the aquifer to rainfall events.Hydrograph analysis revealed that the delay time of spring discharge after rainfall events mostly varies between 10 to 30 days.The total dynamic storage volume of the spring for a given period(2019-2020)was estimated to be approximately 1324 million cubic meters reflecting the long-term drainage potential and high perdurability of dynamic storage.Estimating the maximum and minimum ratio revealed that the springs recharging system in Germi Chai Basin comes under the slow aquifers category.This finding provides valuable insight into the hydrogeological properties of fractured rock aquifers contributing to effective water management strategy.

A Two-parameter Exponential Recession Model for Simulating Cropland Soil Moisture Dynamics

To simulate the soil moisture variation in cropland, a two-parameter exponential recession model was derived to depict the recession process of soil moisture in the root zone. The model is based on the assumption that the recession rate of soil water is proportional to the potential evapotranspiration rate and the difference of soil water content and steady soil water content. Two parameters in this model are soil texture-dependent recession constant and steady soil water content. The model was calibrated and validated with measured soil water data at two experiment sites in North China with different soil textures and cropping systems. Coefficients of determination between measured and model simulated soil water content were all greater than 0.7, indicating that both models gave satisfactory simulation results. Results showed that values of two parameters mentioned above are both larger for finer soil than those for coarser soil. At the same potential evapotranspiration rate and soil water content, the recession rate of finer soil is usually lower than that of coarser soil. The proposed model can be used in irrigation management to predict approximate date for irrigation, as well as be embedded into watershed hydrological models to estimate the antecedent precipitation index.

Study of the Impact of Climate Change on Water Resources in the Sangha Watershed at Ouesso Hydrological Station, Republic of the Congo-Brazzaville (1961-2020)

The Sangha River basin is the largest sub-basin of the Congo River basin, which drains the northern part of the Republic of the Congo-Brazzaville. It is the most important economic zone in this part of the country, with a strong timber industry, agriculture and hydroelectricity. The catchment also boasts the country’s third-largest river port, located in the town of Ouesso. Unfortunately, increasingly frequent low-water levels in recent years have led to a decline in river navigation and economic activities. So, the aim of this study is to show the effects of climate change over the last six decades in the Sangha watershed at Ouesso hydrological station, located in the north of the Republic of the Congo-Brazzaville, and elucidate its impact on water resources. To achieve this, several statistical and hydrological methods were used. The application of change-point or shift detection tests to flow series from 1961 to 2020 revealed variability in the hydrological cycle, characterized by two major phases of homogeneous flows: a wet surplus phase and a dry deficit phase. The results show one shift in flood flows in 1971 (Buishand test), one shift in yearly average flows or modules in 1971 (Pettitt test and Buishand test), and one shift in low-water flows in 1976, with all two tests. These disruptions were accompanied by a drop in flow of around 15.63%, 21.70% and 35.67%, on average, for floods, modules, and low-water, respectively, a drop in rainfall of around 9.6% and a rise in temperature of around 0.76?C. These flows show an overall downward trend. The calculated recession coefficients show that, over the entire study period, a recession occurred in March 1985.

Surface Flood and Underground Flood in Xiangxi River Karst Basin： Characteristics, Models, and Comparisons

Xiangxi River Basin, located in western Hubei Province in central China, is a karst ridge-trough area with an inhomogeneous and complicated distribution of water resources. This paper compares the characteristics of surface and subsurface floods in this karst basin, utilizing a one-parameter Darcian model and the traditional exponential model. The observed hydrographs and inferred water components are strikingly similar for surface and subsurface floods. The Darcian model and the exponential model are based on different views of the flood generation process, with the former fitting the entire hydrograph with a single time constant, and the latter fitting only the recession limb with multiple time constants. Due to the anisotropy and heterogeneity of karst media, a combination of physical and chemical techniques including the use of 3S（remote sensing, geographical information system, global positioning system） method is proposed for an enhanced hydrological investigation to assess and characterize karst water resources in mountainous areas.