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SURFACE WATER

SURFACE WATER. water cycle ( hydrological cycle) = continuous movement of water between atmosphere and earth’s surface STEPS: 1. evapotranspiration = processes of evaporation and transpiration occurring together a. evaporation = when liquid water changes into water vapor

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SURFACE WATER

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  1. SURFACE WATER water cycle (hydrological cycle) = continuous movement of water between atmosphere and earth’s surface STEPS: 1. evapotranspiration = processes of evaporation and transpiration occurring together a. evaporation = when liquid water changes into water vapor 1) heat from sun causes change to occur 2) usually on surface areas b. transpiration = plants give off water vapor to the atmosphere 1) occurs through pore spaces of plants as they breathe

  2. 2. condensation = water vapor cools and expands becomes tiny water droplets a. air is saturated b. will form clouds 3. precipitation = process by which water falls from clouds to earth’s surface a. clouds can no longer hold water vapor b. can be rain, snow, hail, or sleet c. 75% falls in the oceans d. 25% falls on land surface

  3. Water goes in several directions: 1. runoff = water that flows over land into streams and rivers; usually downslope 2. soak into ground forming groundwater 3. absorbed by plants → transpiration 4. evaporation → surface areas such as lakes and streams 5. may be added to a glacier

  4. Factors that determine runoff: 1. amount of rainfall a. rate of precipitation exceeds infiltration b. ground may already be saturated 2. time span over which rain falls: torrential downpours too fast for water to infiltrate ground 3. slope of land: a. steep slopes cause more water loss b. steeper the slope, faster the water flows

  5. 4. amount of vegetation: low vegetation or barren areas have more water loss 5. physical and chemical composition of soil affects water-holding capacity a. soils with high percentage of coarse particles has large pores between particles to hold water and allow it to pass through b. soils with high percentage of fine particles (clay) tends to clump together and has few or no spaces between particles therefore water cannot pass through as easy

  6. water budget = gains and losses of water from a region 1. precipitation is a gain 2. evapotranspiration and runoff are losses 3. world water budget is balanced due to amount of precipitation equaling amount of evapotranspiration and runoff 4. local water budget = one of a particular area a. usually is not balanced b. factors that affect: 1) temperature 2) presence of vegetation 3) wind 4) amount of rainfall 5) duration of rainfall 6) season of the year c. factors can vary geographically

  7. STREAM/RIVER SYSTEMS 1. made up of a main stream and all feeder streams a. all flow downslope to lower elevations b. path varies depending on slope of land and type of material through which stream flows 2. tributary = feeder stream that flows into main stream a. each one increases size of stream it is joining and adds water to it b. large stream is called a river c. small streams are called brooks or creeks

  8. 3. development: a. local precipitation exceeds evapotranspiration b. gully forms = narrow ditch eroded into land surface by running water c. each time it rains gully is eroded wider and deeper d. eventually a fully developed valley with permanent stream forms 4. watershed (drainage basin) = all of land area whose water drains into a stream system a. can be small or extremely large areas b. divides = ridges or elevated regions of high ground that separate watersheds c. each tributary has its own watershed and divides but are all part of larger stream system

  9. stream loads = materials carried by a stream 1. dissolved load = mineral matter carried in liquid solution a. how much is carried in solution depends on material through which water has passed b. groundwater adds most of dissolved load to stream, while runoff adds small amounts c. expressed as parts per million (ppm) 2. suspended load = sediment carried in suspension, free from contact with stream bed a. particles of fine sand and silt b. amount of material suspended varies with volume and velocity of water c. faster moving water can carry larger particles d. as water slows, heavier particles will begin to settle out

  10. 3. bed load = sediment transported on or immediately above stream bed a. larger, coarser material like gravel and pebbles b. saltation = movement of material by short jumps c. material is also moved by sliding or rolling on stream bed d. greatest erosional effect due to abrasion e. pothole = bowl shaped cavity in bed caused by large rocks being scraped over one area in a whirlpool motion

  11. STREAM CHARACTERISTICS 1. banks = edges of stream channel above water level 2. bed = part of stream channel below water level 4. carrying capacity = ability of stream to transport materials a. depends on both velocity and amount of water moving b. channel’s slope, depth, & width all affect speed & direction of water movement 5. discharge = volume of water that flows over a specific location within a given time period a. affected by velocity of water b. high velocity = high discharge = high erosion c. discharge = width X depth X velocity (m3/s) (m) (m) (m/s) d. as discharge increases, carrying capacity increases, erosion increases

  12. 6. gradient = change in elevation of stream over a given horizontal distance a. determines velocity of stream b. can vary along a stream channel c. headwater region will have steep gradient → high velocity 7. water gap = deep notch left where stream erodes through mountain as it is uplifted 8. wind gap = water eroded notch in mountain through which water no longer flows

  13. flood = when water spills over sides of stream’s banks onto adjacent land 1. floodwater carries large amounts of eroded sediments 2. as floodwater recedes, its volume and speed decrease, causing water to drop sediments 3. flood stage = level at which a stream overflows its banks and crest of stream is maximum height 4. it takes time for runoff to collect in streams, which causes water to continue to rise and may reach its crest days after precipitation has stopped 5. upstream flood = flooding of a small area, cause a lot of damage in short period

  14. 6. downstream floods = heavy accumulations of excess water from large regional drainage systems; heavy water volume, extensive damage 7. flood monitoring and warning system a. monitored by National Weather Service b. have established gauging stations = provide continuous record of water level in each stream c. warning system is first step in implementing emergency management plans d. allows people to safely evacuate an area in advance of the flood

  15. Stream Development: 1. changes in shape, width, size, and landscapes over which it flows 2. first and most important condition is adequate supply of water 3. headwaters = region where water first accumulates to supply a stream a. usually high in mountainous areas b. path not well defined when first begins to flow

  16. 4. stream channel = narrow pathway carved into sediment or rock a. network formed by main streams and its tributaries b. widens and deepens as more water accumulates and cuts into surface 5. stream banks = ground bordering stream on each side which holds water within area of stream 6. mouth = area of stream that leads into ocean or another large body of water a. streambed’s gradient flattens out and its channel becomes very wide

  17. Stream Erosion: water erodes more sediment than any other erosional agent 1. headward erosion = process of lengthening and branching of stream a. usually at upper ends, extends river system and watershed b. carries away sediments from slopes of watershed c. usually relatively small and narrow, often form waterfalls over steep inclines d. also called headward extension 2. stream piracy (stream capture) = capture of a stream in one water- shed by stream with higher rate of erosion in another watershed

  18. 3. rill erosion = water swiftly running down a slope creates small channels in soil a. begins when small stream forms during heavy rain b. leaves a scar on slope 4. gully erosion = rill channel that becomes broader and deeper 5. sheet erosion = water flowing over a gentle slope slowly removes sediment from entire land surface 6. erodes a V-shaped channel into region a. continue to erode until it reaches base level = elevation at which it enters another stream or body of water b. lowest base level = sea level

  19. STAGES OF A RIVER SYSTEM 1. young rivers = produces a V-shaped valley with steep sides a. found in mountainous or hilly regions b. may have white water rapids and waterfalls c. high level of energy d. erodes bed more than banks e. few tributaries and usually carries a small volume of water 2. mature rivers = curving stream that flows down a gradual slope and erodes its sides a. well established tributaries and carries more water b. gradient less steep = flows less swiftly → channel gets wider c. erodes valley walls and widens valley floor gradually forming U-shaped valley

  20. d. velocity of water in a river is fastest at the center 1) increases on outside of river bends 2) decreases on inside of curves e. forms meanders = wide curves that form in streams 1) will continue to develop and become wider over time 2) after some degree of winding common for stream to cut off f. oxbow lake = water remaining in an isolated meander in a floodplain 1) crescent shaped lake forms 2) ends become plugged with sediment 3) will eventually dry up g. found at bottom of mountains and hills Oxbow lake formation

  21. 3. old rivers = flows very slowly through a very broad, flat floodplain that it has carved a. gradient and velocity decrease b. no longer erodes land c. causes changes in the meanders d. fewer tributaries e. begins to deposit sediment in channel and on banks 4. rejuvenated river = gradient has been made steeper by movement of earth’s crust a. stream will resume process of downcutting toward its base level b. cut more deeply into valley floor c. cause increase in stream’s flow rate and channel will become V-shaped again d. if meanders are present then deep side canyons could be formed

  22. STREAM DEPOSITION 1. as water velocity decreases the ability to carry sediment decreases 2. delta = triangular shaped deposit at mouth of a stream a. shape and size determined by waves, tides, off-shore depths, and sediment load of stream b. occurs when a stream or river slows as it empties into an ocean, gulf, or lake c. sediments build up & slow stream water, sometimes even blocking its movement d. usually made up of consist of silt and clay e. surface is relatively flat

  23. 3. alluvial fan = fan shaped deposit with its tip pointing upstream a. occurs where stream descending steep slope reaches a flat plain b. common in arid and semiarid regions; dry, mountainous regions Ex: Death Valley, CA c. deposited on dry ground d. contains coarse, angular sand and gravel e. form at the base of slopes 4. bar = elongated mound of sediment in stream channel

  24. 5. floodplain = broad, flat valley floor carved by a meandering stream a. often covered with water if stream floods b. spring floods common near headwaters in areas where the winters are harsh c. ice jams increase chance of spring flooding d. human activities contribute to flooding - removal of natural ground cover e. commonly swampy areas 6. natural levee = raised riverbank that results when a river deposits its load at river’s edges a. can be quite high and prominent on old channels b. usually coarser sediment c. can be on both banks

  25. LAKES & FRESHWATE R WETLANDS 1. lake = depression in surface materials of landscape that collects and holds water a. gain water from streams and runoff b. get water from local precipitation, springs, and other sources c. most have outlets from which water flows to rivers and to ocean d. reservoirs = lakes made for primary purpose of storing water for community’s use e. ponds = manmade lake used for watering livestock, attracting wildlife, natural beauty, etc.

  26. 2. lake formation a. oxbow lakes form when meanders get cut off from main stream b. could also be formed when stream flow becomes blocked by sediment from landslides c. could be remnants of prehistoric lakes that have receded to lower lying areas d. some are formed by glacier movement e. kettle lakes = formed when blocks of ice left by melting glaciers eventually melted in depression f. can also be found in areas where limestone bedrock is located → water dissolves holes and forms caverns

  27. 3. undergo change a. precipitation, runoff, and underground sources maintain a lake’s water supply b. depression that receives more water than it loses to evaporation or use by humans will exist for a long period of time c. considered temporary water-holding areas d. over hundreds of thousands of years, usually fill with sediment and become part of new landscape Volcanic lake

  28. 4. eutrophication = process by which lakes become rich in nutrients from surrounding watershed causing a change in the kinds of organisms in the lake a. animals that live in lake use water’s oxygen and add waste products to water b. amount of dissolved oxygen helps determine quality of water and ability to support life c. can be sped up with the addition of nutrients (fertilizers) d. may cause excess algae and excess organisms that feed on algae which may use too much dissolved oxygen causing fish and other sensitive organisms to die

  29. 5. wetland = land area that is covered with water for large part of year a. bogs = receive water from precipitation, waterlogged soil rich in peat moss, acidic soil b. freshwater marshes = form along mouths of streams and in areas with extensive deltas c. swamps = low lying areas often located near streams 1) may develop from marshes 2) prehistoric swamps formed coal reserves used today

  30. 6. wetlands improve water quality a. act as filtering system that traps pollutants, sediments, & pathogenic bacteria in water sources b. provide vital habitats for migratory waterbirds c. provide homes for many other types of wildlife 7. in the past humans have filled in wetlands to create more land to build on 8. preservation of these have now become a global concern

  31. FLOOD CONTROL 1. flooding is natural stage of development of stream a. will continue to occur as stream matures b. best to leave floodplains in natural state in areas 2. indirect methods: forest and soil conservation that prevents excess runoff during heavy rainfall 3. direct methods a. building of a dam b. building of artificial levees c. create floodway = permanent overflow channel

  32. PREVENTING LAND EROSION: 1. planting vegetation 2. build terraces = broad, steplike cuts made into the side of a slope 3. put up retaining walls Terraces Stream retaining wall

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