GEOL 101 1nd Edition Lecture 20 Outline of Last Lecture I. Hydrologic CycleII. Running WaterIII. Stream FlowOutline of Current Lecture I. Stream ValleysII. Other Stream FeaturesIII. FloodsCurrent LectureStream Valleys-Floodplain deposits- Natural levees – form parallel to stream channel by successive floods over many years- Back swamps – marshy lands between the levels and the valley walls-Yazoo tributaries – small streams that run parallel to the main river, situated between the leveeand the valley wall.Stream Valleys- Consists of stream channel as well as surrounding terrain-The shape of a typical stream valley changes from the headwaters to the mouth:-The gradient is steeper at the headwaters, which causes valley deepening- Result valley is V-shaped- Downward erosion dominates, and develops features like rapids and waterfalls- Towards the mouth of the river, the gradient is more gentle, allowing for valley widening- Stream begins to meander side to side- This widens the valley and develops features such as floodplains, oxbows, yazoos, etcThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.-Meanders – bends in a stream or river-Cut bank and point bar- Cut bank – outside of a meander, erosion is active- Point bar – inside a meander, deposition is active-Cutoffs and oxbow lakes- As the streams mender, part of meander can be cut off from the rest of the river- These segments can form oxbow lakes-Incised meanders- Caused by a drop in base level or uplift of the region by tectonic forces- Meanders are carved in steep, narrow valleys- Common in the Colorado Plateau-Terraces- Remnants of a former flood plain- River has adjusted to a relative drop in base level by downcutting-Drainage patterns are formed by the network of streams in a given area-Common drainage patterns:- Dendritic--irregularly branching tributarieso Most common type- Radial--streams diverge from a center pointo Typical streams flow off of volcanoes- Rectangular--streams bend at right angleso Caused by fractures in the bed rock that are perpendicular to each other- Trellis--rectangular pattern where tributary streams run roughly parallel to each othero Form in areas of alternating resistance and less resistant bedrock-Flood – any event where the amount of water in a stream is too much for the channel to hold-Floods are the most common and most destructive geologic hazard-Floods may vary depending on the terrain of the land and the intensity and duration of the rainfall-Types of floods:- Regional floodso Caused by a long-duration precipitationo Flood waters cover a large geographic area- Flash floodso Caused by intense short-duration precipitationo More localized areas Commonly narrow canyons act as funnels Urban areas do not allow for infiltration, so runoff is maximized- Ice-jam floodso Ice flowing along partially frozen rivers may block part or all of the channelo The ice creates a dam, causing water to flood over its banks- Dam failureo Man-made and natural dams may fail under any number of circumstanceso Too much water from previous floods, earthquakes,
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