Hydrogeology Journal (2015) 23: 1617–1626 DOI 10.1007/s10040-015-1288-4 Spatial variability of streambed vertical hydraulic conductivity and its relation to distinctive stream morphologies in the Beiluo River, Shaanxi Province, China Weiwei Jiang & Jinxi Song & Junlong Zhang & Yuanyuan Wang & Nan Zhang & Xinhua Zhang & Yongqing Long & Jiaxuan Li & Xiaogang Yang Abstract Streambed vertical hydraulic conductivity (Kv) sediments are significantly different on each side of the is a key parameter in the analysis of interactions between channel. The erosional and depositional forms are one of streams and aquifers, and of stream ecosystems. However, the driving dynamics for the distribution of streambed knowledge of the streambed hydraulic conductivity grain size that trigger the differences in the distribution of associated with different stream morphologies is relatively the Kv. scarce. An in-situ standpipe permeameter test method was used to determine the spatial variability in streambed Kv Keywords Geomorphology . Streambed vertical hydraulic measured along 18.5 km of stream reach in the Beiluo conductivity . Erosion and deposition . Groundwater/ River, Shaanxi Province, China. The 59 total measure- surface-water relations . China ments were conducted at four test sites in three different stream morphologies: straight channel, anabranching channels and a nearby meander bend. There was great Introduction spatial variability in Kv among the four test sites and three K distribution patterns can be determined: (1) higher K v v Accurate estimation of streambed hydraulic conductivity values appear on the erosional bank in contrast to lower K fi K values on the depositional bank at the two sites near ( ) is of signi cance in the analysis of the magnitude and v extent of water exchange and contaminant transfer meander bends; (2) the Kv distribution in straight channels shows that the higher K values occur in the center of the between groundwater and surface water, and is even v important in dealing with a number of geotechnical channel; (3) the Kv values are generally highest on the branch with more alluvial forms in the anabranching problems involving the management of groundwater and surface water (Cardenas et al. 2004; Chen et al. 2008; channels. Moreover, grain-size analysis results illustrate K that the average grain-size distributions of streambed Song et al. 2009; Sebok et al. 2014). Streambed can be measured through a variety of approaches and techniques which have been discussed by Landon et al. (2001) and Received: 15 December 2014 /Accepted: 19 June 2015 Published online: 14 July 2015 Kalbus et al. (2006). It should be taken into account, however, that each method has its own limitation because * Springer-Verlag Berlin Heidelberg 2015 of measurement scale and field conditions (Kalbus et al. 2006; Min et al. 2013). It is known that the streambed W. Jiang I J. Song I J. Zhang I Y. Wang I Y. Long I J. Li I X. Yang vertical hydraulic conductivity (Kv) always varies spatial- College of Urban and Environmental Sciences, ly; some studies have revealed that the Kv has large Northwest University, Xi’an, 710027, China variations along a river transect (perpendicular to the river J. Song ()) flow direction; Chen 2005; Min et al. 2013). Streambed State Key Laboratory of Soil Erosion and Dryland Farming on the Kv is spatially variable in a river and the occurrence of the Loess Plateau, largest Kv is in the center of the stream channel (Genereux Institute of Soil and Water Conservation, CAS & MWR, Yangling, et al. 2008). Landon et al. (2001) and Chen (2005) 712100, China K e-mail: [email protected] reported that v variation could occur on a scale as small as 3 m. In addition, even over a short distance (less than N. Zhang K Yellow River Institute of Hydraulic Research, Zhengzhou, hundreds of meters), the v can change appreciably (Chen 450003, China 2004; Genereux et al. 2008). Moreover, hydraulic con- ductivity decreases with increasing depth according to the X. Zhang State Key Laboratory of Hydraulics and Mountain River study results of Song et al. (2010) and Min et al. (2013). Engineering, The channel morphologic features are important factors Sichuan University, Chengdu, 610065, China in the analysis of the hydraulic relationship between 1618 streams and aquifers (Cardenas et al. 2004; Käser et al. is relatively scarce. In the present study, the study focuses 2009; Sebok et al. 2014). Hyporheic interaction is on an investigation of spatial variability in streambed Kv controlled by variable pressure heads in the streambed spanning 18.5 km of stream reach in the Beiluo River, sediments and its environmental conditions (Koch et al. Shaanxi Province, China. An in-situ field standpipe 2011). Stream morphologies create the pressure variations, permeameter was utilized to collect 59 total measurements including meanders (Nowinski et al. 2011), cobbles using 4 test sites in 3 stream morphologies (one in the (Edwardson et al. 2003), bedforms (Bardini et al. 2013), straight stream channel, one in anabranching channels and riffles and pools (Käser et al. 2009), and beaver dams two near distinctive meander bends). All sediment (Genereux et al. 2008). The across-stream gradient can be samples were collected after the Kv tests and they were induced by flow along meander bends, which is enhanced used for grain-size analysis. by the natural alignment of large stream K along the The objectives of this study were to (1) investigate direction of maximum gradient (Cardenas et al. 2004). spatial variability in streambed hydraulic conductivity (2) Compared to homogeneous bedform, small-scale perme- determine the links between this variability and stream ability heterogeneity produces more irregular flow patterns morphologies, bedforms and water depth, and (3) analyze (Bardini et al. 2013). Downwelling and upwelling flow the relationship between the distribution of vertical paths can be caused by bedform and sinuosity at small hydraulic conductivity and the sediment grain size. scale (1–100 m), and width and depth of bedrock at large scale (km; Malard et al. 2002). For a pool–riffle sequence, exchange between channel and hyporheic water can induce rapid downwelling at the head of riffles and varies Study area upwelling in riffle tails (Edwardson et al. 2003). Furthermore, regional groundwater-flow attributes are The field study was conducted in the Beiluo River, which predominately controlled by stream geomorphology such is one of the tributaries of the Weihe River, and is a as channel gradient, sinuosity, width/depth ratio, stream- meandering stream located in Shaanxi Province, China. bed hydraulic conductivity and so on (Larkin and Sharp The river system has a feather-like distribution with a total 1992). It has been reported that either bankfull cross- length of 680.3 km, and the total area of the Beiluo River sectional area or bankfull width are significant for all peak Basin is approximately 26.9 km2. It covers two Chinese discharges (Lawlor 2004). High hydraulic conductivity topographic regions, the Loess Plateau and the Guanzhong produces saturated subsurface flow (Irvine et al. 2012). Basin. Its flow is from northwest to southeast and empties The interaction of streams and aquifers can be enhanced into the Weihe River. The study area is located in a by growth of meander length and reduced by decrease in continental monsoon climate area and has a mean annual river sinuosity (Boano et al. 2006). Due to the transport of precipitation of 541.7 mm and a mean temperature of fine materials, the hydraulic conductivity of shallow 13.2 °C. Seasonal variations in precipitation are distinctive alluvial aquifers under condition of sinuosity-driven and non-uniform. The majority of floods occur from July hyporheic flow is dynamic (Nowinski et al. 2011). to October. The river system has a stream gradient of 1.98 A meandering stream is one of the important sedimen- ‰ and the average stream flow is 14.99 m3/s. This area is tological forms that connects regional aquifers and streams in the transition region between the Loess Plateau and the (Dong et al. 2012). Sebok et al. (2014) demonstrated that Guanzhong Basin. The streambed sediment is alluvial there are more variable streambed features in the meander loess sandy clay and sand-gravel stratum of Pliocene and bend than in the straight section. The existence of several Holocene Epoch. Meandering channel morphologies orders of magnitude in range of streambed anisotropy occur because of the change from an erosional regime to values has been observed close to stream banks (Sebok a depositional regime. et al. 2013). The water exchange in the main channel can The Beiluo River is an important local river that move into slower pools by anabranch diversions, and provides water supplies for agricultural activities and promotes the exchange process into the subsurface (Koch human consumption (Zhang et al. 2007). However, et al. 2011). A combined study of the Kv and erosion and because of a long history of wastewater drainage and deposition processes of streambed sediments has been platform runoff from nearby rapidly developed petroleum conducted by Genereux et al. (2008) and Levy et al. industries, the natural environmental systems have been (2011). Bardini et al. (2013) showed that the bedform is an affected. In this process, the Beiluo River has received important hydrologic factor impacting hyporheic water contaminants and has been influenced by the input of a exchange. The streambed and point bars influence the large amount of organic matter and heavy metals (Shi process of water exchange and solute transport between et al. 2008). Furthermore, the annual average amount of streams and surrounding groundwater systems (Dong runoff for the Beiluo River has markedly decreased, et al. 2012). Those previous studies suggested that there especially from spring to autumn, during the period from are many influences on hydraulic conductivity including 1964 to 2008 (Dong et al. 2014). Therefore, determination stream morphology and geomorphology attributes, river- of the hydraulic conductivity of the Beiluo River’s bed forms, erosion and deposition process, and the riverbed is essential for estimating the water discharge riverbed sediments.