Three‐dimensional model of modern channel bend deposits

Abstract

[1] We present a three-dimensional model of heterogeneous modern channel bend deposits developed through purely structure-imitating interpolation (kriging) of hydraulic properties. This model, augmented with ground-penetrating radar data and directional variograms, agrees with detailed observations in similar modern environments and leads to a process-based interpretation of the presented hydraulic conductivity structure. Integration of all available information permitted delineation and characterization of the modern streambed as a distinct hydrostratigraphic unit without coring or outcrop studies. Our results imply that the modern streambed is commonly oversimplified in available analytical and numerical models of groundwater-surface water interactions where it is assumed to be homogeneous and isotropic and characterized by a constant width and thickness. This three-dimensional approach that integrates concepts and principles developed in sedimentology, hydrogeology, geophysics, and geostatistics has potential implications on model development of stream-aquifer systems.

Spatio‐temporal variations of hyporheic flow in a riffle‐step‐pool sequence

“…In some cases, the distribution of bed permeability may be attributed to sediment sorting (e.g. Cardenas and Zlotnik, 2003;Ryan and Boufadel, 2007). This can hold for the riffle versus pool pattern (discussed later), but the deposition of finer sediments next to eroding banks seems counter-intuitive, as the velocity of stream water is indeed higher in the outer part of the bend, where erosion shapes the bank.…”

“…Nevertheless, such heterogeneity also controls exchange patterns, both at the bedform scale and the reach scale (Wroblicky et al, 1998). In streambeds, permeability can be expected to exhibit strong 3D variability over a few metres (Cardenas and Zlotnik, 2003;Conant et al, 2004), and can be altered by erosion/deposition processes occurring over time scales of years (Ryan and Packman, 2006), seasons (Genereux et al, 2007) or days (Wondzell and Swanson, 1999).…”

Effects of Streambed Conductance on Stream Depletion

“…Along the length of a stream, the streambed naturally exhibits spatial variability of C [20][21][22][23][24][25][26][27][28], which, combined with aquifer heterogeneity, has been shown to affect the small scale and intermediate scale water fluxes between the stream and the aquifer. In a field investigation of fluxes along a stream reach that is 60 m long, Conant [29] found the fluxes can vary significantly in both magnitude and direction.…”

Evaluation of the streambed leakage concept in analytical models using data from three pumping tests

“…It is instructive to check the magnitude of l using independent estimates of characteristic parameters at the site. Experimental data of Cardenas and Zlotnik (2003), which were collected in the summer of the year 2000, yielded K′=15-20 m/day using various averaging techniques for hydraulic conductivity of the streambed sediments from constant-head injection tests. They also proposed to use the depths of scour surfaces as a proxy for the streambed thickness m′; estimates of this value from ground-penetrating radar surveys indicate that m′ varies between 2 and 3 m. With the stream width W varying between 10 and 20 m (Table 1), an estimate of l= (WK′)/m′ yields values between 60 and 100 m/day.…”

“…In spite of the recent progress in streambed characterization, the problem of in situ determination of the hydraulic conductivity distribution and alluvial architecture (delineation of the streambed) remains. Small-scale hydraulic testing and geophysics (Bierkens and Weerts 1994;Butler et al 2002;Cardenas and Zlotnik 2003;Ritzi et al 2004) can be used with upscaling to obtain these parameters at scales commensurate to modeling applications. However, these types of studies are labor-intensive and time-consuming and are, thus, limited to site scales of 10 0 -10 1 m.…”