Basic Hydrology

1. Basic Hydrology Water Quality: Sediment production and transport

2. Sediment in streams • The significance of sediment in streams has two aspects • the water quality aspect is related to suspended sediment • unwanted suspended sediment can cause domestic water quality problems, and can cause physical damage to fish • supply and movement of coarse sediment in streams is a channel morphology issue • excessive coarse sediment in streams can adversely affect fish habitat and fill in water control structures

3. Sediment movement in streams • Sediment movement in stream channels can be categorized by grain size or by the process that transports it • suspended sediment consists of fine particles of silt and clay that are carried by the water column • suspended sediment movement is independent of flow rate • wash load is a term that refers to sediment that is carried by the water column, that has grain size distribution smaller than the channel bed

4. saltating bed load • consists of fine to medium sand • movement is dependent on the velocity of flow: at low flow it may not move, but at high flow it may bounce high up into the water column • behaviour may be similar to suspended sediment for fine sand at high flow • bed load consists of coarse sand, gravel and larger sized particles that are transported by rolling along the channel bed. • bed load transport is also dependent on flow rate • there is a threshold flow velocity needed to get it moving

5. Grain size classes

6. Sediment production vs. transport • Sediment production refers to the addition of new sediment to the channel system • landslides • surface erosion • channel bank erosion • Sediment transport refers to the movement of sediment that is already in the channel system

7. Types of sediment transport systems • Supply limited • most rivers are supply limited in terms of sediment production • the stream has the ability to move all the sediment that is supplied to it, hence sediment transport is limited by the supply • sediment transport tends to exhibit pulse behaviour, sediment movement occurs mostly on the hydrograph rising limb • hysteresis occurs where sediment concentration for a given flow is greater for rising than falling streamflow

8. Suspended sediment pulse, Russell Creek

9. SS concentration vs. discharge 19 - 20 November 1991 Russell Creek Supply limited Rising Falling

10. Spray River near Banff, 1973 Supply limited

11. Sediment transport types • Transport limited • transport limited sediment transport is far less common than supply limited • occurs when the sediment supply to the stream is in excess of the ability of the stream to transport it • occurs in braided and anastamosed rivers where sediment supply is high • as a result, more sediment moves on the falling limb than the rising limb of the hydrograph • hysteresis occurs where sediment concentration for a given flow is greater for falling than rising streamflow • large rivers can exhibit both types of transport behaviour

12. Dual behaviour of large rivers • Large rivers tend to be transport limited during freshet periods • sediment concentrations tend to be high during spring freshet because • flow is low - sediment is “concentrated” • sediment production occurs as a result of supply of sediment accumulated over winter that enters the system all at once • As flows increase, they become supply limited • sediment transport capability increases

13. Fraser River at Mission, 1983

14. Transport vs. supply limitedFraser River 1983 transport limited April supply limited May - June rising falling falling rising

15. Columbia River 1976somewhere south of Golden transport limited event

16. May 1976 Columbia River Falling Rising

17. Measurement of suspended sed. • Direct method: sample analysis • a sample of stream water is collected using a manual DH48 depth integrated sampler or an automatic sampler such as ISCO 3700 • the sample is filtered through a 2 mm filter to determine sediment concentration in mg/l • Indirect method: turbidity is measured and interpreted as SS conc. by field and lab calibration

18. Sediment production processes • rain splash erosion • sheet wash erosion - surface runoff • freeze-thaw erosion • expansion and contraction of erodible rock surfaces • frost expansion • needle ice development • animal movement • ravelling of loose sediment surfaces • undercutting and slumping of loose surfaces • mass wasting

19. Factors controlling sediment production • Cause of runoff • rainfall produces more sediment than an equivalent volume of snowmelt • rain erosion on exposed sediment sources vs. water yield from snowpack that blankets the exposed sed. • rainfall produces larger peaks than streamflow, hence greater sediment transport and channel scour • Size of storm • larger storms generally produce more sediment • larger yield, and greater peak concentration

20. Controlling factors • Watershed morphology • lithology: softer more erodible bedrock (e.g., basalt - Catherine Cr.) produces more sediment than harder more resistant bedrock (e.g., granite - Russell Creek) • type and connectivity of sediment sources • debris flow deposits are big producers • hillside sediment sources • landslide scars, road cuts • slope stability

21. Controlling factors • Land use, e.g. logging and related activities • related to other factors such as slope stability and surface erosion from road surfaces and cut and fill slopes • increase in mass wasting processes following logging • yarding disturbance • potential increase in streamflow after logging • increase in sediment transport capability • increase in stream channel and bank erosion

22. Sediment Production at Russell Cr.

23. How does logging affect sediment production? • Studies show that increased sediment after logging is related to logging roads • surface erosion from road surfaces • road related landslides • Open slope failures increase after logging • If soil disturbance is minimized, clear-cuts are not sediment sources • burning • ground skidding