River Systems - Runoff

Running Water Integral part of sculpting the Earth’s surface MOST IMPORTANT AGENT OF EROSION Indirectly results in the formation of sedimentary rocks

Stream Formation Sheetflow or Sheetwash – overland flow of water Repeated precipitation events cause a preferential channel to form – downcutting Tributaries form & the main channel continues to grow up slope – headward erosion

Stream Morphology Streams increase in length by headward erosion – erosion occurring at the beginning of the stream Streams become wider through lateral erosion – mass wasting of the stream banks Streams become deeper through downward erosion of the channel by abrasion of the sand and gravel

Fig. 11.13

Stream Terminology Stream System – main stream plus tributaries Drainage Basin – area drained by main stream and tributaries Drainage Divide – area of higher elevation that divides drainage basins Function of size/scale For Example: Kickapoo Creek Sangamon River Illinois River  Mississippi River

Stream Terminology Stream System Drainage Basin Drainage Divide Function of size/scale Fig. 11.7

Fig. 11.6

Stream Subsystems Collecting System Transporting System Tributaries is head water region Funnel water and sediment to main channel Primarily erosion and transport Transporting System Main tributary Main process is the movement of the sediment and water Erosion, transport, and deposition all occur Dispersing System Distributaries at mouth region Primarily deposition of the sediment Coarse sediment along the confluence Fine particles carried further in to body of water

Drainage Patterns Fig. 11.8

Streamflow Dynamics Examine the physical and hydraulic properties of the stream Discharge Velocity Gradient Channel Properties Wetted Perimeter Shape Size Roughness Sediment Load

Daily Question Duplicate the chart to the right. On the chart add lines that represent how the following properties change: Discharge Velocity Cross-Section Area Gradient Channel Roughness Base level The property “drainage basin area” is provided as an example

Discharge (Q) Volume of water passing a given point over a specified length of time (length3/time), generally given in ft3/s or m3/s Calculated by: Where A is the cross-sectional area (length2) & v is the velocity of the water (length/time)

Velocity The speed of the water at a given point along a stream Directly related to a stream’s ability to erode and transport material High velocity water can carry heavier sediment Is a function of Gradient Channel Properties Wetted Perimeter Shape Size Roughness

Stream Gradient Slope or steepness of the stream channel Vertical drop (relief) of a stream over a fixed distance Controls the potential energy of the water Steeper the gradient – the higher the velocity, the lower the gradient – the lower the velocity Meanders decrease the gradient by increasing the horizontal distance of the stream

Wetted Perimeter The area in which water touches the channel walls Channel shape and size controls the wetted perimeter Most efficient streams have small wetted perimeters Roughness of the channel controls the frictional resistance to water movement A smooth channel decreases frictional force A rough channel increases frictional force