We describe the first detailed reach-scale study of an incisional till-bed river. Our analysis focusses on boundary till characteristics, bare patch features, annual erosion rates, bedform dimensions and spacing, grain size distributions bedforms. Results show that exposures constitute a relatively small portion bed rates are high compared to bedrock rivers, although highly variable between pat...

Field studies of forest gravel-bed rivers in northwestern Washington and southeastern Alaska demonstrate that bed-surface grain size is responsive to hydraulic roughness caused by bank irregularities, bars, and wood debris. We evaluate textural response by comparing reach-average median grain size (D50) to that predicted from the total bank-full boundary shear stress (t0bf), representing a hypo...

The geometry of a river bed surface is determined by the arrangement and size of the particles that form the bed. In gravel-to-boulder bed rivers, the surface geometry around any individual particle may be complex and highly variable, and tends to include multiparticle structures. These textural and structural characteristics influence whether an individual particle is entrained. The effect on ...

The lowermost Mississippi River, defined herein as the river segment downstream of the Old River Control Structure and hydrodynamically influenced by the Gulf of Mexico, extends for approximately 500 km. This segment includes a bedrock (or more precisely, mixed bedrock-alluvial) reach that is bounded by an upstream alluvial-bedrock transition and a downstream bedrock-alluvial transition. Here w...

In large rivers, complex sediment dynamics cause rapid changes in the position and shape of bed deposits. Regular monitoring of changes in river bed geometry is essential for assessing the nature of morphological change and associated bed load during low, high, and medium flow conditions. We demonstrate the application of Direct Sampling (DS) for patching partial river morphological surveys to ...

The effects of exposed pipe encasements on the local variation of hydrodynamic and sediment conditions in a river channel are examined. Laboratory experiments are performed to assess the response of water level, flow regime and bed deformation to several representative types of concrete encasements. The experimental conditions considered are: three types of exposed pipe encasements exposed on t...

Depending on their grain sizes (settling velocities), sed iments are t ransported in rivers as bed load, in suspens ion , or as wash load. The coarsest material rolls or bounces along the bot tom as bed load whereas finer material is placed into suspens ion by the water turbulence. The finest sed iments are t ranspor ted as wash load. evenly distr ibuted through the water depth and effectively ...

This study addressed a research concern that employing fixed value for the bed roughness coefficient in lowland rivers (mostly sand-bed rivers) is deemed practically questionable presence of mobile and time-dependent changes vegetation patches. Accordingly, we set up 45 cross-sections four streams to investigate seasonal flow resistance values within year. The results revealed significant sourc...

rivers are unstable environments affected by natural or human factors in changing their directions and patterns. in this study, the tectonic effects on the pattern of the gharasou river in the north of kermanshah city have been studied. aerial photos (years 1955 & 1990), satellite images (etm, year 2000) and topographic as well as geologic maps were used as research tools. the procedure of the ...