Hydraulic Geometry and Theory of Equilibrium Water Depth of Branching River

Abstract

Based on the flow continuity formula, resistance formula, sediment transport capacity formula and width-depth ratio relationship, the hydraulic geometry relationship and theory of equilibrium water depth for a branching river are established and are suitable for arbitrary section shape. The ratio of cross-sectional area of a distributary channel and the main stream is a power function of its bifurcation ratio with an exponent of 6/7. This was applied to a 12.5 m deep-water channel of the Yangtze River (the North Passage, Fujiangsha Waterway and Shiyezhou Waterway). The reliability of the equilibrium water depth was verified and the construction effect of the channel regulation project was predicted. The results show that the regulation project has achieved certain results on the whole, but some waterways still cannot meet the requirement of 12.5 m navigation depth. It is necessary to adjust the layout of the regulation project and focus on increasing the bifurcation ratio and reducing the flow resistance so as to increase the maximum equilibrium water depth.

Morphological Evolution of Euphrates River Cross-Sections in Central Iraq: Response to Streamflow and Sediment Load Variability

“…This is happened due to the spiral movement of water current when the main water is rapidly moving and collides with the concave area [23]. A reactionary water current is down warded and works slowly with a quantity of sediments that have been deposited in the convex side [24]. Also the barrier islands are play a large role especially in the straight parts as at sites of the course for generation water stream running towards outer side of meander resulting in the scouring in it as at site 612+730 km [25].…”

“…The river bars are played a large role in formation floodplains as their continued growth which leads to added new lands, which consequently increase the area of the floodplains [24], especially, if their components are cohesive through the natural plant, which will grow over the time [26]. The bars range of channel section consists of "strip adjacent" to the bank extending along the length of the bank have formed due to the combination of some reasons, including: Low water level and lack of discharge with the presence of a large load borne by the river water, especially in the summer or drought season and with reduction in longitudinal slope and direction of river stream.…”

“…If the result is less than 15% then the islet is "strip", and between 15 and 26% the islet then is "longitudinal". While the percentage between 26 and 30% the island or bars is "arc", and between 30 and 45% the island is "irregular "in shape, but if the result is between 46 and 57% the island is "round", and between 60 and 90% sorting as "semi-regular" in shape [24,25]. Different shapes of island have taken in studied reach including "Oval", or irregular because of the difference in their dimensions Islands in studied reach are divided into; "Permanent islands" which types of islands surrounded by water from all sides throughout the year, which has been clear morphological features from long time period of time as in sections sites 605+00 km, 609+860 km, 612+620 km, 615+720 km, 616+630 km, and 620+550 km.…”

“…As a part of expansion by current of flow due to processes of scouring and transportation from banks would provide opportunity to be middle barriers in the river stream. In addition, with the time there is a more increase in river expansion through the decline of the original banks, it will help to increase the growth of the island located in this location of river course [24].…”