GEOLOGY 102 Lecture 31 – Streams 1) Introduction and Definition a) When more water falls on the land that can ________________ into the ground – referred to as _________________________ b) _____________________ - water that flows on the land surface c) Running water transports _____________________ products - eroded from higher areas to lower areas d) By far, the most dominant ______________ shaping the Earth’s surface e) _____________________ - a body of water, confined to a ________________, which flows under the influence of ________________ i) Regardless of size 2) Forming Streams a) A stream channel _____________________ by erosion up slope __________________________________________ b) ______________________________ form in the area at the same time c) Array of _______________ streams evolves – forming a drainage network 3) Parts of a Stream a) _____________________ - outlet of a stream b) headwater - source of a stream c) ___________ - floor of a stream d) _____________________ - flat land on either side of the stream that becomes covered with water during _____________________ e) _____________________ - smaller streams f) _____________________________ - larger stream that tributaries flow into g) _____________________ - specific segment of a stream i) ____________ reaches – lie near the _____________________ ii) ____________ reaches – lie near the _____________________ 4) Stream Flow a) Laminar flow – water particles travel in _____________________ line paths that are ________________ to the channel i) No mixing ii) _____________ velocity iii) Occur in smooth channels b) Turbulent Flow - water moves in a _______________, erratic fashion i) Whirlpool eddies ii) Due to ___________________ of water particles and __________________ of particles by obstacles (rocks) iii) Turbulent flow common in: (1) _________________ water (2) shallow streams (3) Stream flowing in a _______________, gravelly channel 5) Stream Parameters a) _____________________ - slope of a stream = i) Typically decreases downstream b) _____________________ - rate of flow = i) Directly related to gradient c) Discharge (___) – volume of water that passes a ______________ in a given period of _____________ as it flows through a channel of a certain width and depth i) _________________________________ ii) Depends on 2 factors: (1) _______________________________ (2) _______________________________ Q = AV = w x d x V iii) Measured by a stream-_______________ station (1) Well measures the ____________ of the water (2) A current meter measures the ____________ iv) Varies along along a stream’s path v) Can also vary with time (_____________________) vi) All water in a stream _____ _______ travel at the same velocity vii) _____________________ at the channel surface slows the flow viii) Water ___________ the channel walls and floor moves more ______________ than water in the ______________ of the flow ix) _______________ flow lies near the _______________ in the center of the channel d) _____________________ - deepest part of a channel i) In a _____________ stream, the thalweg shifts to the _____________ of a curve ii) Water flows in a ____________ motion 6) Work of Running Water i) 3 components: (1) _____________________ load: material carried in ______________ (a) Ions released by weathering (b) Nitrates, calcium carbonate (2) _____________________ load: material being carried in _____________ (a) Bulk of sediment carried by a stream (b) Intermittent or permanent (c) ______________ particles _______________ faster (3) __________ load: material carried along the ____________ by rolling or sliding (a) Moved by water ______________ or grain collisions (b) Material _____________________ (c) Mainly large particles, > sand-sized ii) any place where a stream’s velocity ____________ down, the stream’s ability to carry sediment decreases and sediment is _________________ iii) What causes water to slow down? (1) If water passes from a ___________ part in the stream to a ______________ part (2) If water _________________ out over a floodplain (a) In both cases - _______________ between the bed slows water down (3) If water enters a _____________________ body of water (4) When the _____________________ of a stream (the downstream slope ) _____________________ 7) Changes along a stream’s length a) _____________________ Profile – a crosssection showing the variation in a stream’s _____________________ along its length i) Roughly _____________________ curve ii) Gradient is _____________________ near the headwaters than the mouth iii) Near headwaters: flows down deep _____________ and _____________, over water falls iv) Near mouth: flows over nearly ____________________ plain 8) Stream Patterns a) Meandering vs. Braided i) Function of (amount of _______________ (climate), type of ________________ carried, stream gradient) b) _____________________ stream – single, sinuous channel with broadly looping curves, or meanders i) Common on _________ gradient slopes – coastal areas & midcontinents ii) Typically form ___________ valleys iii) _______________________ - sediment deposited on the _____________ of a meander (1) Composed of relatively coarse material (2) Grows by ________________ accretion iv) _____________________ - erosional bank on the ________________ of a meander (1) Energy of the river focused on the outside of the curve (2) Material eroded and transported ________________ v) A stream gradually works its way across the valley by ________________ on one side and ________________ on the other side (1) A stream wants to follow a more _______________ route (2) Eventually a meander will be ________________ forming an oxbow lake (3) ________________________________ (4) Later, the lake fills with ________________ vi) __________________________ - part of the stream valley subject to ________________ (1) Grows by ________________ deposition c) _____________________ Stream – many channels that ___________ apart and then rejoin i) Large variations in flow ability to carry sediment, high sediment _________, and easily ________________ banks ii) Usually found near _____________________, ________________ areas, or ________________ climates i) Areas with ________________ discharge d) ________________ - a wedge of sediment formed where a stream enters ________________ water, the current _____________, the stream loses it’s ability to carry sediment, and sediment ________________________________ i) River tends to divide into small streams (___________________________) (1) Mississippi River deltas (a) Indicate that the main ________________ of the river has ________________ on several occasions (b) Occur when the ________________ builds so far out into the sea that the ________________ of the stream becomes to ________________ to allow the river to flow 9) Floods a) A flood occurs when the ________________ of water flowing down the stream ________________ the volume of the stream ________________ i) Water rises out of the normal channel and ___________________________ over the floodplain ii) Flooding stream is more ________________, has more ability to carry sediment, and exerts more ________________ on structures in its path iii) When do they occur? (1) During abrupt, heavy rains - ________________ > ________________ (2) After a long period of continuous rain – ground is ________________ (3) When heavy snows melt rapidly (4) When an artificial or natural ________________ suddenly collapses iv) Flood stage - water surface in the stream is ________________ than the ___________ of the normal channel (1) Takes time to develop – hours to days v) Prediction (and prevention?) (1) U.S. Army Corp of Engineers (2) Built 300 + dams along tributaries of the Mississippi River – store ________________ ________________ in reservoirs to be released ________________ (3) ________________________________ - sand and mud levees and concrete flood walls to ________________ the channel’s volume (4) Could not contain the 1993 flood (a) ________________________________ - increasing water pressure on the river side ________________ water through the levee to the dry side vi) Other ways (1) Transforming parts of the ________________ back into natural ________________ - wetlands ________________ water like a sponge (2) ______________________ - regions likely to be flooded – abandon or move buildings located in these regions vii) ________________________________ Interval – the average ___________ between successive floods of a given ________________ (1) Depends on ________________ of the flood (______________________) (2) The ________________ the flood, the ________________ the recurrence interval, ________________________ the flood with occur in a given year