Chapter 6 Notes.docx

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University of Manitoba
Geological Sciences
GEOL 2390
William M.Last

Chapter 6 Notes Rivers and Flooding Floodplain the flat surface adjacent to the river channel that is periodically inundated by flood water. It is produced by the process of flooding hydrology the study of the water cycle involving the transport of water thought evaporation to the atmosphere, fall to the land by precipitation, and runoff the land into the oceans drainage basin (or watershed) region drained by a shingle river or river system river slope or the vertical drop of the channel over some horizontal gradient distance base level theoretical lowest lever to which a river may erode, most often at sea level longitudinal a graph of elevation of a river against distance downstream Profile total load the total quanitiy of sediment carried in a river, includes bed load moves by the bouncing, rolling, or skipping or particles along the bottom of the channel, usually composed of sand and gravel and less than 10% of total load suspended composed mainly of silt and clay, carried above the load streambed by the flowing water, accounts for 90% of the total load and makes river look muddy dissolved load carried in chemical solution and is derived from chemical weathering of rocks in the drainage basin Discharge (Q) The volume of water moving by particular location in a river per unit time Continuity Discharge calculation Q=W X D X V equation W = width of flow D = depth of flow V = velocity of flow Alluvial fans Streams that flow from mountains onto plains that form fan-shaped deposits Delta rivers flowing into the ocean or some other body of water of water that deposit sediments in a triangular or irregular shaped landmass extending into a sea or lake distributary many channels that carry flood waters to different parts of channels the fan or delta, may change position rapidly during a flood dynamic steady state between the work done (sediment equilibrium transported) by the stream and the load imposed (sediment delivered) to the stream from the tributaries and hill slopes Ventura Beach Planners did not recognize that the park was constructed RV Resort on a historically active distributary channel, engineering models that predict flood inundation are inaccurate when evaluating distributary channels, historical documents were not reviewed that would have shown the distributary channels were present Channel The configuration of the channel as seen in an aerial view, pattern can be braided or meandering Braided Channels characterized b numerous gravel base and islands channels that divide and reunite the channel, steep slop and coarse sediment occur Meanders Bends that migrate back and fourth across the floodplain, cutbank is on the outside of the bend (erosional) and point bars are on the inside (depositional) Pools Deep areas produced by scour, or erosion at high flow and characterized at low flow by relatively deep slow movement of water Riffles Shallow areas produced by depositional process at high flow and characterized by relatively shallow, fast moving water at low flow Flooding The natural process of overbank flow, a function of the total amount and distribution of precipitation in the drainage b
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