Isotope hydrograph separation in alpine catchments:a review

Isotope hydrograph separation （IHS） is a basic tool in applied hydrology. Its application has expanded to surface water and groundwater interaction, and eco-hydrological processes from runoff generation processes. This paper reviews the progress made in IHS for alpine catchments, with emphasis on its significance in reflecting the impact of global change on water resources. Also, the principle of IHS and its uncertainties are explained in detail. The mechanism of variation of stable isotopes in snow-melt water is discussed, and then methods are presented to improve the separation during snow-melt such as volume weighted average method （VWA）, current melt-water method （CMW） and runoff-corrected event water approach （RunCE）, with their advantages and disadvantages explained. New approaches may extend the applications of IllS, for example, large basin studies combined with GIS, and develop new theories of runoff generation combined with other pararneters such as deuterium excess and DOC.

Hydrological modelling in the anthroposphere: predicting local runoff in a heavily modified high-alpine catchment

Hydrological models within inflow forecasting systems for high-alpine hydropower reservoirs can provide valuable information as part of a decision support system for the improvement of hydropower production or flood retention. The information, especially concerning runoff, is however rarely available for the calibration of the hydrological models used. Therefore, a method is presented to derive local runoff from secondary information for the calibration of the model parameters of the rainfallrunoff model COSERO. Changes in water levels in reservoirs, reservoir outflows, discharge measurements at water intakes and in transport lines are thereby used to derive the local, "natural" flow for a given sub-catchment. The proposed method is applied within a research study for the ?BB Infrastructure Railsystem division in the Stubache catchment in the central Austrian Alps. Here, the ?BB operates the hydropower scheme "Kraftwerksgruppe Stubachtal", which consists of 7 reservoirs and 4 hydropower stations. The hydrological model has been set up considering this human influences and the high natural heterogeneity in topography and land cover, including glaciers. Overall, the hydrological model performs mostly well for the catchment with highest NSE values of 0.78 for the calibration and0.79 for the validation period, also considering the use of homogeneous parameter fields and the uncertainty of the derived local discharge values. The derived runoff data proved to be useful information for the model calibration. Further analysis, examining the water balance and its components as well as snow cover, showed satisfactory simulation results. In conclusion, a unique runoff dataset for a small scale high-alpine catchment has been created to establish a hydrological flow prediction model which in a further step can be used for improved and sustainable hydropower management.

Springs Emerging along the Elevation Gradient Indicate Intensive Groundwater-Surface Water Exchange in an Alpine Headwater Catchment, Northwestern China

Groundwater plays an important role in sustaining the streamflow in cold alpine area, but is poorly understood due to a lack of direct access. About 98 groups of springs are observed at the upper reaches of Heihe River Basin, which provide an opportunity to explore the main aquifers. Springs are clustered in three groups according to locations:(1) springs on the moraine and talus deposits;(2) springs at the end of alluvial plain in lower topography;(3) springs along the river bank. The hydrometric, geochemical and isotopic data of springs in a representative catchment were integrated and used to elucidate the groundwater flow paths. Results indicate the Quaternary porous aquifers in the alpine catchment have a profound influence on the regional groundwater flow paths and the groundwater and surface water(GW-SW) interactions. The aquifer consisting of alluvial-pluvial deposits has a great capacity of groundwater storage and plays a vital role in regulating discharge by attenuating the seasonal variation and maintaining the main stream in cold seasons. This is different from the fast recharge and discharge mode of the moraine and talus deposits. Our work highlights the importance of loose deposits in controlling the GW-SW interactions in the cold alpine area.

Runoff and sediment yield in relation to precipitation,temperature and glaciers on the Tibetan Plateau

The riverine sediment is an essential carrier for nutrients and pollutants delivery and is considered as an important indicator of land degradation and environmental changes.With growing interest in envi-ronmental changes over the Tibetan Plateau,this study investigated mean annual runoff and sediment yield from eight headwater catchments in relation to annual precipitation,air temperature,and glacier area ratio,etc.Results show that runoff(Q)is positively correlated with both precipitation(P)and temperature(T),i.e.,Q¼0.357Pþ20.3T-6.4,indicating combined water supply from rainfall and melt-water,increase of which may exceed the evapotranspiration water loss caused by temperature raise.Sediment yield(S)shows an inverted parabolic relationship with precipitation and at the same time positive correlation with glacier area ratio(Ag),i.e.,S¼0.000609 P2-0.470Pþ48.5 Agþ202.53,indicating that sediment yield is a minimum at about 500e600 mm of precipitation,increasing sharply on both sides of this minimum in one case owing to decreased vegetation protection and in the other to enhanced erosive power and that erosion rate in the glacierized area is generally higher than non-glacierized area.The variation in sediment yield with precipitation can be explained by the operation of two factors,i.e.,rainfall erosive action that increases continuously with increase in precipitation,and vegetation protective action that is unity for zero precipitation and decreases with increases in precip-itation.The above results may be useful in visualizing not only variations in rates of erosion among climatic zones on the Tibetan Plateau but also the probable changes of erosion during a climatic change.