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Groundwater is the major source for resident drinking, industrial development, and agricultural irrigation in the Huai River Basin (HRB). With the development of industry and agriculture, exploitation of the deep groundwater increases dramatically in the HRB in recent years. Therefore, analysis and evaluation the renewability of the deep groundwater in the HRB is critical. In our study, a total of 390 groundwater samples were collected along four profiles in 35 cities and counties within the HRB to obtain their hydrochemical characteristics and isotopic data. Based on the isotopic data of these samples, three deep groundwater subsystems: the Shaying River System, the Guohe River System, and the Ancient Yellow River System were identified. The further comparison indicates that the deep and shallow groundwater systems of Guohe River System and Shaying River System have good differentiation. While, the connection of deep and shallow aquifer of Ancient Yellow River System is strong. According to the calculation results based on the combination of stable isotopes and water chemistry, the renewable ability of deep groundwater of Ancient Yellow River, Shaying river, and Guo river are 36%, 22%, and 12%, respectively, which implies faster renewal rate and greater exploitation potential. [ABSTRACT FROM AUTHOR]

Rainfall-runoff relation is the basic and critical issue in hydrology, as well as in the hydrologic experiments. Supported by Chuzhou Hydrology Laboratory, this study conducted experimental investigation of the rainfall-runoff relation of Hydrohill experimental catchment during its historical (1982-1995) and modern (2013-2018) practice periods. Hydrohill is equipped with a separate-runoff system which can measure the runoffs in different layers: the uppermost trough collects rain; the next lower trough collects surface runoff (RS); the three lower troughs collect subsurface low from soil layers of the depths of 0–30, 30–60, and 60–100 cm (inferred as R30, R60, and R100). A network of 21 aluminum alloy access tubes for neutron moisture gauges were constructed in the historical period. Since the last month of 2012, all aluminum alloy access tubes have been displaced with 31 profile soil moisture sensors (PR2) with six sensor points located at the 10, 20, 30, 40, 60, and 100 cm. Eight profiles with another kind of soil moisture sensors (SM-1) were installed as well since 2017. This type of SM-1 has nine sensor points located at the 10, 20, 30, 40, 50, 60, 70, 80, and 90 cm. An array of 22 galvanized tube wells intersect through the soil till the concrete aquiclude. Water table measurement is performed with pressure-type sensors (LEV1) located at the bottom of each well. According the experiment results, conclusions are determined as following: (1) The proportion of RS decreased from 57.3% during the historical period to 35.3% during the modern period, and thus the runoff structure became subsurface runoff dominated from surface runoff dominated. During the historical period, the proportion of RS accounted for 54.4%, 57.3% and 70.3% under the conditions of 10≤P<25 mm, P≥25 mm, and P<10mm (P represents rainfall amount of events), respectively. (2) the synthetic runoff coefficient of RS decreased while that of R100 increased from historical period to modern period; the synthetic runoff coefficient of R30 decreased but R60 increased under the condition of P≥25 mm. (3) The maximum discharges of all separate runoffs during historical period were larger than those during the modern period. (4) The average rising times of RS, R30 and R60 during historical period were longer than that during the modern period, but R100 was just the opposite. The average peak times of RS during historical period were shorter than those during the modern period. The duration of all separate runoffs in both catchments were during historical period were longer than those during the modern period. (5) The depths of soil distinction layers were located at the range of 30-40 cm based on the data of profile soil moisture. (6) Saturated overland flow just occurred in the unchanneled upstream based on the analysis of the dynamics of water table in Hydrohill. This investigation can enhance the in-depth understanding of rainfall-runoff relation in the small headwater catchments. [ABSTRACT FROM AUTHOR]

Hydrology, to date, has confronted its developmental bottleneck due to lack of newmonitoring and experimental data for hydrological processes in watersheds. Fortunately, newconcepts and techniques have been emerging to better meet the demands in the acquisition ofnew monitoring and experimental data. In addition, some artificial experimentalcatchments or watersheds, whose boundaries and inner structures can be designed anddefined in advance, have been established to investigate hydrological processes underwell-controlled conditions. In order to clarify the mechanism and regularity ofwatershed hydrological cycle, this study designs hydrological experiments withcoupled natural and artificial system using two-direction multi-scale approach, i.e.upward and downward. Thus, hydrological experiments at Huashan Watershed inChuzhou City, representative of the low-altitude warm region in China, are designedand being performed by adopting new and advanced monitoring techniques andequipments. Within Huashan Watershed with a drainage area of 80.0 km2, two representativewatersheds are selected: Sanchahe Watershed (17.6 km2) and Huangwa Watershed (2.6 km2).Four smaller catchments act as critical zone experimental blocks, including WangyingCatchment (0.27 km2), Gaochong Catchment (0.08 km2), Nandadish Catchment (0.008 km2)and Hydrohill Catchment (artificial, 0.0005km2). These catchments or watersheds jointogether to form an excellent multi-scale experimental system, including artificial and naturalexperimental blocks. At the outlets of Wangying, Gaochong, Huangwa, Sanchahe, andHuashan watersheds, V-notch weirs grooves and hydrological cables have been combined toobserve total stream discharges. Hydrohill and Nandadish catchments have been wellinstrumented to automatically measure hydrological elements such as precipitation,discharge, soil moisture, groundwater level, and evapotranspiration with high precision. Inaddition to the above measurements of water quantity related hydrological elements,precipitation, stream water, soil water, and groundwater in Hydrohill Catchment,Nandadish Catchment, Sanchahe Watershed and Huashan Watershed are sampled atdifferent location through water sampling systems designed and manufactured byourselves to determine the δ2H, δ18O, EC, pH, DO, and concentration of mainions. Hopefully, the experimental work and results in this site may push forward the emergenceof new data, new discoveries and new ideas for the development of hydrology, especiallyhydrological models. Key words: hydrological experiment; Nandadish; Hydrohill; Chuzhou HydrologicalExperimental Site; coupled natural and artificial system Acknowledgements: This study is supported by the National Natural Science Foundationof China (No. 91647203, 91647111, 41330854 and 41371063) and the Science Foundation ofNanjing Hydraulic Research Institute (No. Y516027, Y516032 and Y517016). [ABSTRACT FROM AUTHOR]

Distribution of residence time has been commonly used to characterize the responsecatchment runoff processes. Most previous studies on water residence time have been mainlyfocused on large scale analysis in time and space and on estimating residence timedistribution of total runoff. In this study, we analyzed residence time distribution (RTD) ofdifferent runoff components at event scale in Hydrohill experimental catchment, which islocated in Chuzhou City, Anhui Province, China. Hydrochemical and isotopic data, i.e., 18O,D, anions (HCO3−, Cl−, NO3−, SO42− and F−), cations (K+, Na+, Ca2+ and Mg2+) anddissolved Si in water samples were collected during the rainfall events in 2016, which areused to characterize the response of different runoff components by combining lumpedparameter models. Results showed that 18O and Cl− are the most suitable indicators toevaluate RTD of runoff components. On the experimental catchment scale, groundwaterrunoff gets the longest residence rime among all three runoff components. Residencerime of interflow runoff is approximately 1.38 times longer than that of surfacerunoff. Hydro-chemical tracing provide an effective way to easily measure andunderstanding hydrological processes for critical zone, which could support hydrologicalmodel development by strengthening physical base of hydrological cycle. However,what caused difference in residence time of runoff components and how to quantifyinteraction between different runoff components should be enhanced in furtherstudy. Key words: water residence time; runoff components; lumped parameter models;hydro-chemical and isotopic data; Hydrohill experimental catchment Acknowledgements: The work has been supported by National Natural ScienceFoundation of China (Grant No. 41830863) and National Key Research and DevelopmentPrograms of China (Grant No. 2016YFA0601501) [ABSTRACT FROM AUTHOR]