1	Running Water, Chapter 9 Geoscience 1 Lancaster High School Mr. Hayhurst
2	Hydrologic Cycle The hydrologic cycle is a summary of the circulation of Earth’s water supply Processes involved in the hydrologic cycle Precipitation Evaporation Infiltration Runoff Transpiration
3	The Hydrologic Cycle
4	Sources of Earth’s Water
5	Running Water Begins as sheetflow Infiltration capacity is controlled by Intensity and duration of rainfall Prior wetted condition of the soil Soil texture Slope of the land Nature of the vegetative cover Sheetflow develops into tiny channels called rills
6	Running Water Streamflow Two types of flow determined primarily by velocity Laminar flow Turbulent flow Factors that determine velocity Gradient, or slope Channel characteristics including shape, size, and roughness Discharge – the volume of water moving past a given point in a certain amount of time
7	Running Water Changes from upstream to downstream Profile Cross-sectional view of a stream Viewed from the head (headwaters or source) to the mouth of a stream Profile is a smooth curve Gradient decreases downstream
8	Running Water Changes from upstream to downstream Factors that increase downstream Velocity Discharge Channel size Channel roughness
9	Longitudinal Profile of a Stream
10	Running Water Base level and graded streams Base level is the lowest point to which a stream can erode Two general types of base level Ultimate (sea level) Local or temporary Changing conditions causes readjustment of stream activities Raising base level causes deposition Lowering base level causes erosion
11	Adjustment of Base Level due to Changing Conditions
12	A Waterfall is an Example of a Local Base Level
13	Running Water Stream erosion Lifting loosely consolidated particles by Abrasion Dissolution Stronger currents lift particles more effectively
14	Running Water Transport of sediment by streams Transported material is called the stream’s load Types of load Dissolved load Suspended load Bed load Capacity – the maximum load a stream can transport
15	Running Water Competence Indicates the maximum particle size a stream can transport Determined by the stream’s velocity
16	Running Water Deposition of sediment by a stream Caused by a decrease in velocity Competence is reduced Sediment begins to drop out Stream sediments Generally well sorted Stream sediments are known as alluvium
17	Running Water Deposition of sediment by a stream Channel deposits Bars Braided streams Deltas Floodplain deposits Natural levees – form parallel to the stream channel by successive floods over many years Back swamps Yazoo tributaries
18	Formation of Natural Levees by Repeated Flooding
19	Running Water Deposition of sediment by a stream Alluvial fans Develop where a high-gradient stream leaves a narrow valley Slopes outward in a broad arc Deltas Forms when a stream enters an ocean or lake Consists of three types of beds Foreset beds Topset beds Bottomset beds
20	The Nile and Mississippi Rivers Exhibit Different Types of Deltas
21	Running Water Stream valleys The most common landforms on Earth’s surface Two general types of stream valleys Narrow valleys V-shaped Downcutting toward base level Features often include rapids and waterfalls
22	Running Water Stream valleys Two general types of stream valleys Wide valleys Stream is near base level Downward erosion is less dominant Stream energy is directed from side to side forming a floodplain
23	Running Water Stream valleys Features of wide valleys often include Floodplains Erosional floodplains Depositional floodplains Meanders Cut bank and point bar Cutoffs and oxbow lakes
24	Erosion and Deposition Along a Meandering Stream
25	A Meander Loop on the Colorado River
26	Running Water Incised meanders and stream terraces Incised meanders Meanders in steep, narrow valleys Caused by a drop in base level or uplift of the region Terraces Remnants of a former floodplain River has adjusted to a relative drop in base level by downcutting
27	Running Water Floods and flood control Floods are the most common and most destructive geologic hazard Causes of flooding Result from naturally occurring and human-induced factors
28	Running Water Floods and flood control Types of floods Regional floods Flash floods Ice-jam floods Dam failure
29	Satellite view of the Missouri River flowing into the Mississippi River near St. Louis.
30	Same satellite view during flooding in 1993
31	Running Water Floods and flood control Flood control Engineering efforts Artificial levees Flood-control Dams Channelization Nonstructural approach through sound floodplain management
32	The Drainage Basin of the Mississippi River
33	Running Water Drainage networks The land area that contributes water to a stream is called the drainage basin Drainage pattern consists of the interconnected network of streams in an area Common drainage patterns Dendritic Radial Rectangular Trellis
34	Drainage Patterns
35	End of Chapter 9