Streams

1. Streams 

2. The hydrologic cycle

3. Sources of Earth�s water

4. Running water Streamflow 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

5. Longitudinal profile of a stream

6. Base level and Graded Streams Base level is the lowest point to which a stream can erode Two types of base level Ultimate (sea level) Local or temporary Graded Streams restore original state Changing conditions causes adjustment Sudden extra sediment steeper gradient, faster flow erosion, sediment removed and equilibrium reestablished. Equilibrium is temporary

8. Stream - Sediment Terminology Transport of sediment by streams Transported material is called load Types of load Dissolved load � ions in solution from weathering Suspended load � fine particles Bed load Moves during high velocity events Sandy Portion � Saltation (bouncing) Cobbles � Traction (rolling) Capacity �maximum load stream transports Competence � Largest particles it can move Proportional to velocity squared

10. Competence maximum particle size a stream transports Proportional to velocity squared �K.E.

12. Stream valleys Most common landforms on Earth�s surface General features of stream valleys 1. Narrow valleys � Very Steep Gradient V-shaped Downcutting toward base level Can include rapids and waterfalls

13. Wide Stream Valleys Low bed load, high suspended load 2. Wide valleys often include Floodplains Erosional floodplains Depositional floodplains Meanders Cut bank and point bar Cutoffs and oxbow lakes Levees

14. Erosion and deposition along a meandering stream

16. Point Bar Sequence

17. Formation of natural levees by flooding

21. Incised meanders Meanders in steep, narrow valleys Caused by a drop in base level or uplift of region

23. Stream terraces Terraces Remnants of former floodplain River adjusts to drop in base level by downcutting

27. Braided Streams Very high bed load, intermittent flow Often adjacent to mountains w/ seasonal flow Mid-channel bars split the stream Many channels

29. Deltas Occur where stream hits slow water Suspended load is dropped Deposits build out into lake or sheltered sea, extending the length of the river Consists of three types of beds Topset beds - horizontal, surface delta Foreset beds - delta slope Bottomset beds � horizontal, bottom sea

32. Groundwater

33. Importance of groundwater Groundwater is water found between grains in sediment, and in narrow fractures in bedrock Groundwater is the largest reservoir of fresh water available to humans

34. Sources of Earth�s water

35. The water table Water table is the upper limit of saturation Variations in the water table Depth is highly variable Varies seasonally and from year to year Shape is usually similar to surface topography

37. Factors influencing movement of groundwater Permeability, aquitards, and aquifers Porosity � Volume of Pore Space Permeability � the ability of a material to transmit a fluid through pore space Aquitard � an impermeable layer that hinders water movement (such as clay) Aquifer � permeable rock strata or sediment that transmits groundwater freely (such as sands and gravels)

38. Springs may result from  a perched water table

39. Features associated with groundwater Hot springs Water is 6-9oC warmer than the mean annual air temperature of the locality The water for most hot springs is heated by cooling of igneous rock

40. Features associated with groundwater Geysers Intermittent hot springs Water erupts with great force Occur where extensive underground chambers exist within hot igneous rock Groundwater heats, expands, changes to steam, and erupts

46. Features associated with groundwater Wells To ensure a continuous supply of water, a well must penetrate below the water table Pumping of wells can cause Drawdown (lowering) of the water table Cone of depression in the water table

47. Formation of a cone of depression in the water table

48. Saltwater contamination due to excessive well pumping

50. Geologic work of groundwater Acidic groundwater dissolves limestone Groundwater is often mildly acidic Rain contains weak carbonic acid Forms when rainwater dissolves carbon dioxide from air Humic acid from decaying plants increses acidity Carbonic acid reacts with calcite in limestone to form calcium bicarbonate, a soluble material Cements particles � lithification Hard water � a problem for pipes

51. Geologic work of groundwater Caverns Features found within caverns Composed of dripstone (travertine) Calcite deposited as dripping water evaporates Includes stalactites (hanging from the ceiling) and stalagmites (form on the floor of a cavern)

52. Geologic work of groundwater Karst topography Landscapes that have been shaped by the dissolving power of groundwater on limestone Some common features include Irregular terrain Sinkhole or sinks (formed by groundwater slowly dissolving the bedrock often accompanied by collapse) Disappearing (aka sinking) streams

53. Karst Topography Sinkhole or sinks (formed by groundwater slowly dissolving the bedrock often accompanied by collapse) Disappearing (aka sinking) streams

55. Florida sinkholesFlorida sinkholes

56. End of Chapter 14