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Understanding Watershed Flux Data and Sediment Transport Dynamics

This document explores the critical interactions affecting river systems, including the influence of large woody debris, atmospheric conditions, and hillslope processes on sediment transport. It details the measurement of sediment loads (bedload, suspended load, and dissolved load) and addresses the complexity of integration over all flows for accurate mass loading assessments. We also examine historical data, such as the 1927 flood, to illustrate the effects of extreme weather on river dynamics. Understanding these factors is essential for effective watershed management and addressing human impacts.

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Understanding Watershed Flux Data and Sediment Transport Dynamics

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  1. Interactions class • Getting and understanding watershed flux data • Influence of Large Woody Debris (LWD) on rivers • Influence of Hillslope materials and processes on rivers • Influence of the Atmosphere on rivers, 1927 flood example

  2. 1 Sediment Transport Through Rivers Bedload -- material moving along the bed, shear forces exerted by water sufficient to move clasts -- rarely measured (at % level) Suspended Load -- material kept in the water column by turbulence and lift forces (easy to measure in grab samples) Dissolved Load -- material in solution (easy to measure in grab samples) Bedload usually <<< than suspended load and ignored Dissolved load varies, usually < than suspended load

  3. 1 Sampling for suspended load…….

  4. 1 Mass Loadings and Erosion Rate Estimation Integrate suspended load over all flows (mass/time) + Integrate bedload load over all flows (mass/time) + Integrate dissolved load over all flows (mass/time)

  5. 1 Dissolvedload varies over time and discharge

  6. 1 USGS Water Quality Data on lineDissolved and Suspended Load http://nwis.waterdata.usgs.gov/nwis/qwdata?site_no=04282815&agency_cd=USGS&begin_date=&end_date=&format=html_table&inventory_output=0&rdb_inventory_output=file&date_format=YYYY-MM-DD&rdb_compression=file&qw_sample_wide=0&submitted_form=brief_list

  7. 1 Data Manipulation Data supplied in mg/l (1/1000 g per 1000 g) or ppm Need to sum all constituents (Ca, Na, Mg, Cl, C03) Need to know daily flow (in liters). How many liters/m3? Multiply concentration by flow m3 = 100 cm* 100 cm* 100 cm = 106 cm3 =103 liters 100 l/s* 60s/min*60min/hr*24hr/day*15mg/l*0.000001kg/mg= 129.6 kg/day dissolved load

  8. 1 TO GET YEARLY LOADIntegration over all flows is a non trivial problem!Need Rating Curves (suspended, dissolved, bedload) Suspended Load Note Scatter Hysteresis loop

  9. 1 Other Approaches…Reservoir trapping (may miss dissolved) Nahal Yael, Negev Desert

  10. 1 SEDIMENT YIELD = what comes out = or ≠ Timescale Steady state Human impact Episodic disturbance SEDIMENT GENERATION = Material generated by erosion

  11. 1 Trimblegram

  12. 2 Importance of Vegetation Bank Stabilization, effective soil cohesion Source, Large Woody Debris

  13. Queets River, Olympic Penninusla, Washington 2 LargeWoodyDebris

  14. 2

  15. 2 Queets -- Meander Jam

  16. 2 Most rivers have been de-snagged Montgomery et al., 2003 Putget Lowland

  17. 2

  18. 2 Reach Scale Effects

  19. 2 In-Channel Effects

  20. 2 Valley Bottom Effects - Wood adds Complexity Nisqually River w/wood Floodplain Elevation (m)

  21. 2 Effects Felt Downstream

  22. 2 • Briaded Rivers • Weak banks • High sediment load • Flashy

  23. 2

  24. 3 Influence of Hillslope Materials and Processes on Channels Slides are frequent in mountain environments Example: Chris Brummer, Squire Creek, North Cascades, Slide into Channel

  25. 3 Toe of Slide - QT VR

  26. 3 Sediment and Woody Debris Supply - pulsed delivery

  27. Stepping of Channel Profile Damming of ephemeral lakes by slides 3 Outlet, overtopping dam

  28. 3 Help set channel roughnessboulders may be delivered by older slides….or underlying bedrock or till

  29. 3 Here, stratigraphic evidence this is not the first slide… Recent Slide Debris Older Slide Debris

  30. 4 1927 Flood • Antecedence --Rainfall during the month of October averaged about 150 percent of normal across the state. In northern and central sections, some stations received 200-300 percent of normal.

  31. 4 Major Channel Change and Realignment - Proctor

  32. 4 Major damage at constrictions, e.g., bridges • Isohyet map

  33. 4 Winooski-Burlington response

  34. 4 Cause of the 1927 Flood Mositure-laden air was forced to rise as it encountered the Green Mountains, resulting in torrential downpours. Rainfall in Northfield totaled 1.65 inches from 4:00 am to 11:00 am on the 3rd, with 4.24 inches falling from 11:00 am to 8:00 pm. The total from late evening of the 2nd to late morning on the 4th was 8.71 inches.

  35. Wednesday Lab • Meet in classroom • Move to the field, Bolton • Cooler weather, be prepared. • Wear sturdy shoes please

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