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Interactions between surface water and groundwater play a major role in hydrological processes. Understanding the seasonal variations of the water exchange is important to clear drivers of water transferring in a catchment. However, the seasonal variations of water exchange have been limited by the resolution of methods and the experimental problems. In this paper, the Weihe River, in Shaanxi Province, China was chosen, as a case study area to access the seasonal variability of water exchange in the hyporheic zone (HZ). Five testing sites were in the main channel of the river, and seasonal field data were collected from fall 2012 to summer 2014. The temperature profiles and heat convection-diffusion equation were applied to analyze the hyporheic water exchange pattern (the type of movement) and its magnitude, as well as characterizing the seasonal variability of the water exchange features. The results indicate that the patterns and magnitudes of water exchange in the hyporheic zone vary significantly in seasons and test sites. The water exchange general in the fall season (71.5 mm/d) is larger than in other seasons (i.e., spring 54.14 mm/d, summer 56.19 mm/d and winter 23.26 mm/d). This study provides the guidelines for the water resources management in different seasons.

Estimation of instream flow requirements for sediment transport (IFRST) in the downstream Weihe River is important for the maintenance of a healthy ecosystem of the river. In this study, the IFRST for the lower Weihe River is estimated on the basis of the observed hydrological data during the period 1960–2001. The results showed that the mean annual IFRSTs for the reach between Lintong and Huaxian and the reach below Huaxian were 6·85 and 7·62 billion m3/year, respectively, and the standard errors were 0·50 and 0·76 billion m3/year, respectively. The results also showed that the Sanmenxia Reservoir is an important driver for the changes in channel morphology and hydraulics, as well as the IFRST. Furthermore, according to the hydrological frequency (p value) estimated from annual instream flow data during the period 1960–2001, four typical years (p = 25%, 50%, 75% and 90%) for the two reaches of the Weihe River were determined. The analysis showed that the IFRST has a negative power functional relationship with the sediment concentration. On the basis of the efficiency coefficients (R2) during three sub-periods 1960–1973, 1974–1990 and 1991–2001, the annual IFRSTs in the above two reaches for the four typical years were estimated under different deposition and erosion–deposition conditions. The results provide useful references for restoration and water resource management of the Weihe River. Copyright © 2010 John Wiley & Sons, Ltd.