GEOL 101 1nd Edition Lecture 19 Outline of Last Lecture I. Radioactivity II. Geologic Time ScaleOutline of Current Lecture I. Hydrologic CycleII. Running WaterIII. Stream FlowCurrent LectureHydrologic Cycle-The hydrologic cycle is a summary of the circulation of Earth’s water supply- The cycle is driven by energy from the sun, whereby the atmosphere is the link between the ocean and the continents-Processes involved in the hydrologic cycle- Precipitation: condensed water molecules that fall from the atmosphere to earth- Evaporation: the transfer of liquid water at the surface to water vapor in the atmosphere- Infiltration: the movement of surface water into the ground through the soil or rock fractures- Runoff: water that flows over the surface, and does not infiltrate into the subsurface- Transpiration: the release of water vapor into the atmosphere by plantsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Running Water-Begins as sheet flow: thin broad sheets of water flowing across the ground- Amount of sheet flow depends on the infiltration capacity of the soil (how much water can seep into the ground)- Infiltration capacity is controlled byo Intensity and duration of rainfallo How wet or dry the soil was before the raino Soil textureo Slope of the lando Nature of the vegetative cover- Sheet flow develops into tiny channels called rills which eventually form larger channels-Drainage Basins:- A drainage basin is the land area that contributes water to a stream- Drainage pattern consists of the interconnected network of streams in an area- Drainage basin of one stream is separated from the drainage basin of another by an imaginary line called a divideo Divides range in scale from ridges separating 2 small gullies, to continental dividesStream Flow-Streams may flow in one of two ways, depending on the velocity:- Laminar flow – slow moving water moves in a relatively straight line- Turbulent flow – faster moving water is more erratic and may have whirlpools, eddies, and rapids-Stream flow velocity is fastest in the center of the channel-Factors that determine velocity:- Gradient – slope, or steepness of the stream- Channel characteristics including shape, size, and roughness- Discharge – volume of water moving past a given point in a certain amount of timeo Calculated by finding the cross-sectional area, and multiplying the area by the stream velocity-Changes from upstream to downstream- Profileo Cross-sectional view of a streamo Viewed from the head (headwaters or source) to the mouth of a streamo Profile is a smooth curveo Gradient decreases downstream (i.e. gets flatter)-Changes from upstream to downstream- As we go from the headwaters down towards the mouth:o Discharge increase as a result of more tributary streams that drain into the main streamo Channel size increases to accommodate more water from the tributary streamso Gradient decreases to a more gentle slopeo Channel roughness decreases with a gentler slope- Base level is the lowest point to which a stream can erode.o Two general types of base level: Ultimate (sea level) Local or temporary (lakes, resistant rock layers, larger main layers)Work Done -Streams are the earth’s most important erosion agents- Streams erode, transport, and redeposit massive amounts of sediment-Erosion by streams- Stream currents may dislodge clay, silt, sand, and even larger particles from the stream bed and carry those particles along with the currento Stronger currents pickup small and larger particleso Weaker current can only pick up clay and silt- Stronger currents carrying larger particles are able to scour and erode the stream bed faster than slower currents carrying small particles- Transport of sediment by streamso Material that is being transported by the stream is called the loado Types of load Dissolved load – material that is a solution from the chemical erosion of soluble rocks (limestone, marble, rock, salt, rock gypsum)  Suspended load – Silt and clay sized particles that are carried with the current Bed load – coarse particles (sand-sized increase) more along the bottom of channelo Capacity – the maximum load a stream can transport-Deposition of sediment by a stream- As a stream loses velocity, such as when it reaches its base level it cannot continue to carry its load- Sediment begins to drop out and form deposits known as alluvium- Stream sediments are generally well sorted- Deposition may occur in any number of areas along the stretch of the river- Examples: include point bars, braided streams, sand and gravel bars deltas-Areas where alluvium is deposited:-Channel deposits:- Barso May be in the middle of a channelo May be on the inside of a stream meander- Braided streams – many channels that interlace, very commonly associated with glaciers and deltas- Deltas – fan shaped areas of deposition of mouth of river that flows into the