1. Drainage Basins

2. Hydrologic SystemSome of the water evaporated from the ocean falls onto continentalsurfaces. This water makes its way back to the ocean, in part, bysurface runoff. 3. Drainage BasinsA drainage basin is the area that collects water and sediment for aparticular river system. 4. Drainage Basin ZonesMostlyerosionErosion &depositionbalancedMostlydepositionDrainage basins can be divided into three zones based on the relativedominance of erosion and deposition. 5. Drainage Basins & Hydrologic SystemThe collecting zone consists mostly of mountainous regions.Transportation takes place primarily across the stable platform.Deposition occurs predominantly along the coast. 6. Graded ProfileRiver systems strive toward a state of equilibrium, in which a smoothcurve flattens from mountain peaks to the sea shore. 7. Base LevelBase level is the lowest level to which a stream can flow and iscontrolled by lake or sea level. 8. Graded Profile ChangesAny change to a graded profile eliminates earlier conditions ofequilibrium, and a new profile is developed. Changes are relatedmostly to tectonic movements or fluctuations in base level. 9. Photo by W. W. Little 10. Photo by W. W. Little 11. Photo by W. W. Little 12. Collecting ZoneThe collecting zone is found mostly in mountainous regions and isdominated by erosional processes, such as downcutting, headwardadvancement of channels, and slope retreat. 13. DowncuttingDowncutting is the vertical entrenchment (deepening) of a channel.Downcutting typically represents tectonic uplift but can reflect thelowering of base level. 14. Photo by W. W. Little 15. Photo by W. W. Little 16. Headward ErosionPhoto by W. W. LittleHeadward erosion is the lengthening of a channel due to theconcentration of runoff at the point where the channel begins. 17. Landscape DissectionHeadward erosionproceeds until thelandscape, typically aplateau, becomescompletely dissected.Once streams fromopposite sides meet,headward erosionceases. 18. Headward Erosion & Base LevelEither faulting or a change in base level can disrupt stream equilibrium.A new profile will develop, in part, through headward erosion. 19. Slope RetreatSlope retreat is the widening of a channel, due primarily to processes ofmass wasting (e.g. landslides). 20. Mass WastingSlumpSlideFallFlowCreepMass wasting (or movement) is the downslope movement of rockmaterial under the influence of gravity and can take the form of falls,slides, slumps, flows, or creep. 21. FallsFalls occur when rock breaks loose from a steep to vertical rock faceand drops to the ground. 22. TalusRock falls form cone-shaped accumulations at the base of the slope called talus. 23. Pueblo Bonito, CO 1941 24. Rock AvalanchesLarge masses of rock can break loose and move at high velocities asthey ride over a cushion of compressed air, in a manner similar to snowavalanches. 25. SlidesSlides take place when rock breaks loose and slips down an inclinedsurface, such as a bedding plane or a joint. 26. Vaiont Dam, Italy 27. SlumpsSlumps are large blocks of rock that break and rotate as a single massalong curved surfaces that resemble faults. Flows often occur at thetoes of slumps. 28. FlowsFlows develop when the rock body becomes completely saturatedwith water and moves as a fluid. 29. DeforestationRemoval of vegetation from muddy slopes is a major cause of mud flows. 30. Debris FlowsDebris flows consist of a fluid mixture of mud to boulder-size material. 31. SolifluctionSolifluction is a slow type of flow that takes place in thin layers ofsoil that overly frozen ground. 32. CreepCreep is a slow downslope movement of rock material in response tofreeze-thaw cycles. 33. Creep ProcessesIf the ground is damp, freezing will cause it to expand perpendicular tothe surface. Gravity then pulls it vertically downward. The result is agradual down slope movement of sediment. 34. Deflection Walls 35. Drainage Systems 36. Moisture Barriers 37. Rock Bolts