Bed-load transport

By trapping the sediment from used alpine waters, reservoirs reduce the transport of suspended load to residual flow reaches. In these sections with a reduced channel flow, the tractive force and shear stress is drastically reduced. This additionally reduces the bed load transport, which may then result in solid matter originating from unaffected tributary streams remaiiung in the main channel, thus significantly increasing the debris-flow hazard for episodic high water discharge [36]. 

Molnar P, Anderson RS, Kier G, Rose J (2006) Relationships among probability distributions of stream discharges in floods, climate, bed load transport, and river incision. J Geophys Res 111, doi 10.1029/2005JF000310 Montgomery DR, Balco G, Willett SD (2001) Climate, tectonics, and the morphology of the Andes. Geology... 

It can be seen in Table 9.7 that the particulate load constitutes by far the most important contribution (88%) of total river discharge of materials to the ocean. The amount carried as solids should be increased by bed load transport, which usually is considered to be about 10% of the total suspended load (Blatt et al 1980). The mean chemical composition of river suspended matter closely approximates that of average shale (Table 9.8). This resemblance is expected because suspended solids in rivers are derived mainly from shales. Sedimentary rocks constitute about 66% of the rocks exposed at the Earth s surface fine-grained rocks, like shales, comprise at least 65% of the sedimentary rock mass. Thus, roughly 50% of surface erosion products come from shaly rocks. 

Laboratory investigations on bed-load transportation and bed roughness (a compilation of published and unpublished data). Soil Conservation Service, U. S. Dept. Agriculture, Washington, D. C. (Mimeographed). 

Tsujimoto, T., and Kitamura, T. (1995) Lateral bed-load transport and sand-rigde formation near vegetation zone in an open-channel, J. Hydroscience and Hydraulic Engineering 13(1), 35 15. 

If the skin friction exceeds the critical threshold for resuspension, sedimentary material is I ifted off from the bottom and is transported into the water body. Grainy particles may also be moved by the so-called bed-load transport that occurs already at a lower threshold. Deposition results from the settling of the sediment particles, if the shear stress falls below a certain limit. The critical thresholds, the settling velocities, and the erosion and deposition rates are material constants derived from experiments (Soulsby, 1997). 

The frequency of occurrence plot given in the right panel of Fig. 19.13 confirms that the regions shallower than 30 m are potential erosion areas, where fluffy layers are washed off with a probability of 10% or more. Naturally, the erosion area is smaller and is affected with lower frequencies if the threshold for incident movement is higher, as for example 1.2 cm/s for the bed-load transport of fine sand, or 2 cm/s for its resuspension. 

In vegetated area, the shear velocity to govern sediment transport is evaluated by using equation 6 from the obtained depth-averaged velocity in horizontal 2D flow analysis, and it is applied to evaluate bed load transport rate, entrainment flux of suspended sediment and so on. 

Bed load transport can be described by the formula proposed by (Ashida Michiue 1972), and written as follows. 

Ashida, K. M. Michiue. 1972. Hydraulic resistance of flow in an alluvia bed and bed load transport rate. Proc., JSCE 206 59-69 (in Japanese). 

Kuhnle R.A. 1992. Bed load transport during rising and falling stages on two small streams. Earth Surface Processes and Landforms 17(2) 191-197. 

Liu C.J. 2004. Experimental study on unsteady open-channel flow and bed-load transport properties. Tsinghua University. 

Ma A.X. Lu Y. Lu Y.J. 2012. Advances in velocity distribution and bed-load transport in unsteady open-channel flow. Advances in Water Science 23 (1) 134-14. 

Jeon, H.S., M. Obana T. Tsujimoto. 2014. Bed roughness boundary layer and bed load transport in vegetated area. Proc. Conf. on Hydarulic Eng., Hong Kong. 

D. M. Hanes and A. J. Bowen. "A granular-fluid model for steady intense bed-load transport," /. Geophysical Research, 90(C5), 9149-9152, 1985. 

Van Rijn, L. C. 1981. Comparison of Bed-Load Concentration and Bed-Load Transport. Report prepared by the Delft Hydraulic Laboratory, Delft, The Netherlands. Report No. 5487, Part I. 

To represent better conditions in situ, a test was established to take into account the abrasive load induced by hydraulic processes on the bank and bottom of waterways. The rotating dmm test (RPG, 1994) was developed for geotextile filter layers under riprap. The single armourstone always has some space that allows rocking movements under hydraulic loads which can abrade the fabric. This test also proved suitable for checking resistance against abrasion of geotextiles that are not protected by armour and are loaded by sediment and bed-load transport. Recovered samples proved the similarity to fabric that was tested in that device. 

The EEDC and SEDZLJ models are based on similar theory for cohesive and nonco-hesive sediment transport and representation of the sediment bed. Both models have the capability to simulate multiple cohesive and noncohesive particle size classes, as well as bed load transport and suspended load transport. There are some key differences between how these models implement sediment transport, however. EFDC calculates net erosion or deposition for a given particle size class at a given simulation timestep. In the case of noncohesive sediments, the net rate of water-bed sediment exchange is defined by the suspended and bed load transport capacities of the water... 

Meyer-Peter, E. and R. Muller. 1948. Formulas for bed-load transport Proc. hit Assoc. Hydr. Struct. Res., Report of 2nd Meeting, Stockholm, Sweden, pp. 39-64. 

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