Topic 12 - Earth Surface Processes: Running Water (Rivers)

1. Topic 12 - Earth Surface Processes: Running Water (Rivers) • Importance of Running Water (Rivers) • Running Water- Sources of River Water- Drainage Basins - Drainage Patterns- Stream Ordering and Basin Morphometry

2. Topic 12 - Earth Surface Processes: Running Water (Rivers) • Open Channel Hydraulics and Downstream Changes:- Channel Hydraulics: Stream Discharge, Velocity, Stream Power, etc.- Hydraulic Geometry and Downstream Streamflow Changes- Stream Channel Flow and Stream Channel patterns- Longitudinal Profile of Stream Channel

3. Topic 12 - Earth Surface Processes: Running Water (Rivers) • Geomorphic Functions of Running Water:- Stream Erosion and Fluvial Landforms- Stream Transportation and Fluvial Landforms- Stream Deposition and Fluvial Landforms • River Rejuvenation • Rver Floods and Flood Controls

4. Importance of Running Water (Rivers) • Rivers serve as highways for moving people and goods since the beginning of human history • A source of irrigation water for agriculture. Ancient Egypt irrigation networks of the Nile River produced food surpluses for its region • A source of domestic and industrial water and utilized for hydro-Electric Power (Tennessee Valley Authority)

5. Importance of Running Water (Rivers) • River is a major human resource and also a source of natural hazards; Global river floods alone are responsible for huge yearly loss of life and property damages • River systems, as part of the hydrologic cycle, are involved in recycling water between the world oceans and continents

6. Importance of Running Water (Rivers) • Running water is found everywhere and the most important agent of denudation surpassing wind, glacier, and ocean waves in sculpturing and producing landforms across the globe

7. Running Water: Sources of River Water • The dominant source of water in stream flow hydrograph is determined by:- climate - geology - topography - soil characteristics - vegetation - land use

8. Running Water: Source of Water in Rivers • Precipitation is the only source of water found in rivers. • Rain water or snow melt water gets to the river through several pathways:- Hortonian Overland Stormflow- Subsurface Storm flow- Saturation Overland Stormflow- Groundwater Delayed Flow

9. Running Water: Pathways of Rainwater to Streamflow Path 1 is Overland Storm Runoff Path 2 is Groundwater/Delayed Flow Path 3 is Subsurface Storm Flow Path 4 is Saturation Overland Storm Flow NOTE: Unshaded top soils are highly permeable Shaded subsoils or bedrocks are less permeable

10. Sources of Water in Rivers: Overland Stormflow • Hortonian Overland stormflow occurs when rainfall intensity is greater than soil infiltration capacity (i.e., the maximum limiting rate soil can absorb rainfall) • Once rainfall intensity > infiltration capacity, water will fill all depression storages • When surface storages are exhausted, water spills as irregular sheet of overland flow called Hortonian Overland Stormflow occur

11. Overland Flow Moves Downslope as an Irregular Sheet After Filling Up All Depression Storages

12. Hortonian Overland Flow (Feet of W.B. Langbein)

13. Sources of Water in Rivers: Overland Stormflow • Horton believed that sheet flow will occur everywhere in the basin during a rain storm • But Betson (1964) argued that only a small portion of the basin contributes Hortonian overland flow to streamflow hydrograph because of differences in soil infiltration capacity even across a small area • Betson idea became known as the partial-area concept of storm runoff generation

14. Sources of Water in Rivers: Overland Stormflow • Horton overland flow velocity ranges from 10 - 500 m/hr as depth of flow reaches 1 cm • Hortonian Overland Storm flow is common in: - urban areas where urban impervious surfaces reduce soil infiltration capacity- farmlands where cropping equipment and animal trampling reduce soil infiltration capacity and- arid lands where soil crusting by intense sun occurs- Construction sites with low infiltration capacity

15. Sources of Water in Rivers: Subsurface Stormflow • Subsurface Flow occurs in well vegetated/forested humid areas where plant roots opening up highly permeable soils for more infiltration • Subsurface flow occurs within the soil layer • Saturation overland flowoccurs along saturated river channel walls where subsurface flow emerges as returnflow +direct rainfall (see figure)

16. Saturation Overland Stormflow Areas at the Beginning (dark color) and End of the Rain Event (light color)

17. Examples of Runoff Producing Areas in the Broad Run Creek Catchment, PA (Dunne & Leopold 1978)

18. Runoff Processes in Relation to Their Major Controls

19. Sources of Water in Rivers: Groundwater Flow • Groundwater/Delayed Flow: It is precipitation water infiltrating deep to become part of the groundwater below the water table. It is delayed flow because it goes through pore spaces and arrives the river several months later • It forms the base flow of rivers and keeps the river flowing all year round • For example: In humid areas, perennial rivers carry water all year round and sustained by the delayed groundwater flow

20. Sources of Water in Rivers: Groundwater Flow • Whereas, intermittent or seasonal rivers carry water only when groundwater table is well above channel floor, especially during the wet season • And when water table is far below the river floor, dry river valley occurs . Intermittent Rivers are common in arid and semi-arid environments • Ephemeral rivers carry water during a rainstorm and dries up shortly after; It does not depend on groundwater supply

21. Drainage Basin • A drainage basin is the land area drained by a river and all its tributaries. • It is the land area where a river and all its tributaries collect all the rainwater flowing through their channels • It is defined by the basindivide (i.e., the highest mountain point) separating rainwater flowing into one river system from another

22. Drainage Basin: Mississippi River Basin Basin is the area the Mississippi River collects all its water

23. Drainage Basin Mississippi River Basin and the Nested Basins of its Major Tributaries

25. Stream Drainage Patterns • Each stream channel displays unique ways its numerous networks of tributaries are connected into a distinct stream drainage pattern • Stream drainage pattern reflects the underlying geologic structure of the basin • The basic stream drainage patterns are:- Dendritic Drainage Pattern- Trellis Drainage Pattern - Rectangular Drainage Pattern- Radial Drainage Pattern- Annular Drainage Pattern

26. Stream Drainage Patterns

27. Stream Drainage Pattern: Annular Pattern Annular (ring) pattern develops on domes (Black Hills) with excavated interior exposing soft layer with curved rivers & outer hogback hard rocks; May cut hard rocks to link circular river at a lower river below

28. Stream Drainage Patterns: Dendritic Pattern

29. Stream Drainage Patterns: Trellis Pattern

30. Drainage Basin and Stream Channel Orders • The concept of stream ordering describes how all the stream channels are arranged, organized, classified and ranked to reveal its size and importance in a drainage basin • Stream ordering was first introduced by Robert Horton in 1945, modified by Arthur N Strahler in the 1950s and Ronald L Shreve • Strahler’s method is the most commonly used. A first order stream has no tributaries and when two first order streams meet at a river

31. Drainage Basin and : Stream Channel Orders junction, a second order stream begins • When a lower order stream meets a higher order stream, it does not change its order • When two second order streams meet, a third order stream begins and the second order stream ends • A fourth order stream begins where two third order streams meet and so on

32. Drainage Basin and Stream Channel Orders • Use the next two diagrams to confirm that the stream order of the streams flowing out of the two drainage basins are fourth order streams • What is the stream magnitudeusing Shreve’s method of thisfourth order stream (Strahler method) in the diagram to the right?

33. Drainage Basin and Stream Channel Orders

34. Drainage Basin and Stream Orders - Shreve’s Method • In Strahler’s method, when a lower stream order meets a higherstream order, the lowerstream order is ignored • Shreve defines stream magnitude as the total number of stream segmentsflowing into it. Streammagnitude is a great predictor of stream discharge

35. Drainage Basin and Stream Orders - Shreve’s Method • Whereas, Strahler’s stream orders are known to be closely related to drainage basin morphometric properties like:- Network Properties: * Drainage density * Stream frequency * Length of overland flow- Areal Properties: * Texture ratio * Circulatory ratio parameter * Elongation ratio- Relief Properties: * Basin relief, etc (see next slide complete list)

36. Drainage Basin and Stream Channel Orders Drainage Basin and Morphometric Properties of Stream Networks

37. Stream Channel Flow • Rivers flow from higher to lower elevations in open channels subject to gravitational and frictional resistance forces • The force of gravity propels the water downslope, while frictional forces prevent the water from moving downslope due to water viscosity and channel surface roughness • In general, open channel flow may be turbulent or laminar

38. Stream Channel Flow • Laminar Flow: Thinlayers of water with flow resistance causedby molecular viscosity;Occurs near channelbed & sustained when Reynold Number (Re) is 500. Velocity Profiles of Laminar & Turbulent River Flows • Turbulent Flow: Mostimportant flow in a river;thicker chaotic flow layersuperimposed on theforward flow of the river;Frictional resistance is dueto molecular and eddy viscosities; Occurs whenVariables Used in describing StreamflowRe > 2000; Re is 500 – 2000, laminar/turbulent flows are present

39. Stream Channel Flow • In natural streams, flow velocity controls the switchbetween subcritical tosupercritical flow • Hydraulic Jump is a suddenchange from supercritical to subcritical flow causing astationary wave and increasein stream depth • Hydraulic Drop occurs when there is a change from subcritical to supercritical causing a drop in stream depth; Common in mountain streams and waterfalls

40. Stream Channel Flow • Bedforms in a sandy alluvial channel change as the Froude number (F) changes (see diagrams): Source: Richard J. Huggett (2017)

41. Discharge and Open Channel Flow Hydraulics • Discharge (Q) is the volume of water passing through a given river cross-section per second and expressed in cubic meter/second (m3/s) or cubic feet/second (ft3/s) • Hence stream discharge (Q) is defined as: Q = wdv where w = channel width, d = channel depth, and v = velocity • Confirm that thestream dischargefor the left channel is 30 m3/s andand that for the right channel is 180 m3/s • Confirm that the stream discharge for the left channel

42. Discharge and Open Channel Flow Hydraulics • Stream discharge in open channel is subject to two principal forces:- force of gravity propelling water down slope to produce tractive force (): = yds where: y = specific weight of water (63.3 Ib/ft3 or 1000 kg/m3), d = depth & s = channel slope

43. Discharge and Open Channel Flow Hydraulics - frictional resistance of water molecules and/or water & channel boundaries • the difference between both forces determines water flow velocity • Chezy derived flow velocity equation from both forces

44. Discharge and Open Channel Flow Hydraulics • Chezy velocity (V) equation is given as: ___ V = C RS where: R = hydraulic radius (cross-section area divided by wetted perimeter) S = channel slope C = smoothness coefficient NOTE:depth-slope product is related to tractive force or shear force on the stream bed

45. Discharge and Open Channel Flow Hydraulics • Manning's velocity (V) equation is an improvement on Chezy's and given as:         1.49V = ------ R2/3S1/2       nwhere:'n' = channel roughness factor

46. Discharge and Open Channel Flow Hydraulics • And channel roughness is controlled by: - grain size of bed & bank material - channel vegetation - channel cross sectional form - alignment of channel plan

47. Discharge and Open Channel Flow Hydraulics • 'n' is often calculated from median grain diameter (D50) as follows: n = 0.016D501/6where:D is measured in mm

48. Discharge and Open Channel Flow Hydraulics • Stream power () is a measure of work expended or energy loss of the stream • Stream power () is given as:  = yQs or = ywdvs • Stream power per unit channel width is: ywdvs = ------- = ydsv w

49. Discharge and Open Channel Flow Hydraulics • Since stream power is the product of tractive force and velocity or  = v = ydsv and • Chezy equation tells us that V2  RS • Therefore,   V3

50. Discharge and Open Channel Flow Hydraulics • Hence, a slight change in velocity greatly increases the amount of work done in a stream channel • Stream energy is expended as follows:- sediment transport = 3-5%- frictional heat = 95%