1 Distribution of Earth’s water Fig. 10.2, p. 267 2 The hydrologic cycle Processes involved in the hydrologic cycle: Fig. 10.3, p. 267 Evaporation & Transpiration Precipitation Infiltration & Runoff 3 The Hydrologic Cycle 4 Drainage basin Def.: The entire area from which a stream and its tributaries receive their water Separated from another drainage basin by a divide http://www.ndsu.nodak.edu/tricollege/watershed/image/wpe1.gif 5 Drainage Basins and Divides Def. Divide: a line that separates two drainage basins Fig. 10.30, p. 289 6 Mississippi River drainage basin Fig. 10.31, p. 290 7 Rivers of North America (lots of them flow Northward!) http://www.worldatlas.com/webimage/countrys/namerica/printpage/nanewriv.htm 8 Picture: The "Continental Divide," the line that separates the Nelson/Red River drainage basin from the Mississippi/James drainage basin is marked by a sign along I_94, midway between Valley City and Jamestown, ND. 9 Classification of Streams Drainage Patterns Flow 10 Drainage Patterns Def: Pattern of the interconnected network of streams in an area 3 common: Dendritic Radial Rectangular (Trellis) 11 Drainage Patterns Fig. 10.32, p. 291 12 Dendritic drainage pattern 13 Flow Does the stream flow on a regular basis or not? 3 types: Perennial Intermittent 1 Ephemeral 14 Stream flow Velocity Gradient Discharge 15 Velocity ft/sec or metric equivalent Fig. 10.5, p. 269 16 Gradient The slope, or vertical drop per distance ft/mile or metric equivalent Fig. 10.7, p. 271 17 Discharge Def: the volume of water moving past a given point per unit time CFS = cubic feet/second = ft3/second = channel width x channel depth x velocity Ex: 100ft (width) x 15ft (depth) x 6 ft/sec = 9000 ft3/sec 18 Laminar vs. Turbulent Flow Laminar: Water flow parallel to bed of stream Turbulent: Disrupted flow 19 Velocity ft/sec or metric equivalent Fig. 10.5, p. 269 20 “Ideal” vs. Typical stream channel velocity profile 21 22 Factors that change downstream: INCREASE: Velocity (because of greater discharge, smoother and larger channel) Discharge Channel size (larger, smoother channel, greater discharge) DECREASE: Gradient Channel roughness 23 Transported material: the stream load Load: The quantity of material transported by the stream 2 Capacity: the maximum load a stream can transport Competence: the maximum SIZE particle a stream can transport 24 1) Dissolved load Mostly from groundwater leaching of soils and bedrock Amount not dependent on stream energy Quantity depends on climate 25 26 2) Suspended load Largest part of the load Controlled by water velocity and the settling velocity of each particle Usually silt or clay 27 Diagram of Load types 28 Suspended load 29 3) Bed load Coarse particles that move along the stream bottom Rolling Sliding Saltation (jump, skip, leap) Do not move constantly <10% of a stream’s load 30 31 Classification of Particle Size Gravel Pebble-cobble-boulder > 2.0 mm Sand 0.06 - 2.0 mm Silt (gritty in your teeth) 0.004 - 0.06 mm Clay (smooth in your teeth) < 0.004 mm 32 Erosion, Transport and Deposition Hjulström Diagram Velocity vs. Particle Size 33 Hjulström Diagram OBSERVED erosive power 3 34 Is there a downward limit to stream erosion? Yes, the downward limit is the base level, the lowest point to which a stream can erode Two general types of base level: Ultimate (sea level) Local (temporary) 35 Longitudinal profile of a stream 36 Changing stream conditions cause: Readjustment of stream activities Raising base level causes deposition Lowering base level causes erosion 37 A waterfall is an example of a local base level 38 Can streams achieve equilibrium? A graded stream is in equilibrium neither eroding nor depositing material but: only transporting material a self-regulating system, constantly adjusting toward equilibrium 39 Fig. 10.8, p. 273 40 Longitudinal profile of a stream 41 Graded stream 4.