Sediment Supply & Hydraulic Continuity: Workshop Review

Transcription

1 Sediment Supply & Hydraulic Continuity: Workshop Review Joe Magner, Ph.D., P.H., P.S.Sc. Minnesota Pollution Control Agency Adjunct Faculty, University of Minnesota

2 Denudation Globally, conventional plowing ~ erosion is 1-2 orders of magnitude > soil production. Ecologically unsustainable. No-till: erosion rates ~ soil production rates, thus sustainable. D.R. Montgomery (2007) Dirt: the erosion of civilization, University of California press, Berkeley, 285p

3 Sediment Pathways & Processes Surface or denudation: sheet, interrill, rill, (stripping off the surface) Hillslope: (sloping area between hilltop and channel) ground water, wetland, ephemeral gully Geotechnical: landslides, mass wasting, bluffs Channel: hydraulic bed scour, toe slope scour, sediment deposition

4 Raindrop Impact K e = 0.5MV 2 K = kinetic energy (ergs or ft-lbs) M = mass of falling raindrop (g or lbs) V = velocity of fall (cm/s or ft/s)

5 Pathways?

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7 Process?

8 Hillslope Saturation?

9 Hillslope Degradation

10 Geotechnical Failure

11 Confluence Aggradation

12 Is sediment always a WQ problem? Sediment Yield: total sediment export from a watershed. Sediment Delivery Ratio: D r = Y s /T s Y s = sediment yield (mass/area/yr) T s = total watershed erosion at measured point (mass/area/yr)

13 Sediment Delivery Ratio (SDR) Function: climate, geology, drainage area, steepness, network density, sinks SDR = sediment yield/total erosion (mass/drainage area/unit time) Y = 95(Qq) 0.65 KLSCP, (Williams, 1975) where: Y = single-storm sediment yield in tons, Q = runoff volume in acre-ft, q = peak discharge in cubic ft/second

14 Fishable and Swimmable Do we know how to restore streams to meet the Clean Water Act goals? 1. Impairment is based on failure to meet water quality standards. 2. Assumed disturbance stressor. 3. What is measured? TURBIDITY = fishable & swimmable? 4. If we measure biological response directly can we infer cause and effect linkages to stressor?

15 WHY?

16 United States Environmental Protection Agency EPA-822-R Office of Water March 2006 Office of Research and Development FRAMEWORK FOR DEVELOPING SUSPENDED AND BEDDED SEDIMENTS (SABS) WATER QUALITY CRITERIA

17 Gather Information 1. Review current designated uses and criteria for a set of waterbodies BEDDED Need to Understand Pathway & Process 1 st, Then BEDDED Synthesize State of Knowledge Analyze Available Data 2. Describe SABS effects on the waterbodies designated uses 3. Select specific SABS and response indicators 4. Define potential ranges in value of the SABS and response indicators 5. Identify a response indicator value that protects the designated use 6. Analyze and characterize SABS/response associations Select Criteria Values 7. Explain decisions that justify criteria selection

18 What drives a water quality (WQ) sediment problem? Intrinsic geologic properties? Climate change? Land use change?

19 Intrinsic Geology

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21 Upper Midwestern Climate Cyclonic (Frontal or Air Mass) Storms: Cold Front: rain behind front, high intensity, short, small area. Warm Front: rain in advance of front, low intensity, long, large.

22 Novotny & Stefan (2007) Overall upward trend in Minnesota streamflow (~1%/yr for 36 stations 1900 s thru 2002). No change in snow-melt runoff. Summer runoff increased. Higher base-flows. More higher flow days. Amplitude of change was strong after 1980.

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24 Story of Disturbance & Recovery 4070 km 2 Watershed in N. Central MN Forest and Wetlands Dominate Landscape Lacustrine Soils: Glacial Lake Agassiz Sparsely Populated and Remote Historical Logging from 1890 s 1937 Current Land Use; Forest Management and Tourism M H S

25 Precipitation, Raw Data- 3 Periods Precipitation- Three Segments, Little Fork River Precip Precip Precip Inches Year Trends for each separate time period: positive, positive & flat.

26 Peak Flow, Raw Data- 3 Periods 25,000 Peak Flow- Three Segments, Little Fork River Peak flow Peak flow Peak flow ,000 15,000 cfs 10,000 5, Year Trends for each separate time period: positive, flat & negative.

27 Functional Process Zones

28 Different Functional Processes: Physical slope Chemical reducing Biological No Fish

29 What defines a Stream? Energy = the capability to do work Power = work/time (units = watt) (channel work = stream power) so, a stream is a response to a continuous energy gradient No gradient (slope) = No stream = ponded water (Lake or Wetland)

30 Stream Fundamentals Potential energy gradient = E = mass*gravity*(elevation) Kinetic energy occurs by virtue of the velocity of flowing water, defined by: E = 0.5*mass*(velocity) 2 Loss of E (via law of Entropy) = heat from friction & transfer of momentum or force = F (units, kg-m/s 2 ) F = (momentum) = (mass)*(velocity) 2

31 Bernoulli s Equation P/(ρg) + V 2 /2g) + z = constant, where: P = pressure (N/m 2 ) ρ = density of fluid (kg/m 3 ) g = acceleration due to gravity (m/s 2 ) V = velocity (m/s) and z = elevation above some datum (m)

32 Stream Fundamentals For a given Q (discharge) there must be conservation of mass, even though the crosssection of the channel may change Section 1, A 1 V 1 = A 2 V 2 at Section 2, thus z 1 + d 1 = V 12 /2g) = z 2 + d 2 + V 22 /2g) + h L Where: d = mean water depth (m) h L = head loss due to energy loss (friction)

33 Flow (Q) = Velocity*Area Specific Stream Energy (given A, Q and S) = E s = d (potential) + (kinetic) V 2 /2g Stream Power = Ω = γavs = QS Unit Stream Power = ώ = Ω /(γa) = VS where: γ = unit weight of water (9803 N/m 3 ) d = flow depth, A = flow width*depth V = velocity, S = slope, and g = gravitational acceleration = 9.8 m/s 2.

34 Energy Balance E = z +V 2 / (2g) + P/ (ρg) Any change in E status of a water parcel as it flows, must correspond to changes in at least one of the above components (elevation, velocity or depth) or Change in surface elevation along the stream E = z

35 How important is Slope? We can determine the energy status by measuring S (channel slope) A stream adjusts its energy status by changing its S A stream losses energy (h L ) to its channel by exerting stresses on the channel (τ = shear stress) h L = function of Mannings n

36 Flow and Resistance from Rosgen (1996)

37 Degradation

38 Aggradation

39 Rush & High Island Creek Watersheds Circa 1900 (After Anderson, 1998) Isolated Depressions

40 Rush & High Island Creek Watersheds Circa 1960 (After Anderson, 1998)

41 Photo, Magner Channel Enlargement

42 Sediment Delivery Ratio?

43 Bankfull or Channel forming from Simon (1989)

44 Stable or Unstable? Lentz Section D, Riffle E le v a t io n h c? Width

45 Knickpoint Knickpoint

46 Loss of Pool Habitat Buffalo Creek 96 bed water srf bankfull x-section riffle crest pool run glide sed depth Elevation (ft) Channel Distance (ft)

47 Knickpoint (Down cutting) Armored Riffle, Class III

48 Class IV Channel widening Midchannel bar formation Photo, Hansen

49 Class V Class VI Channel Evolution in a Ditch?

50 What Happened?

51 Novotny & Stefan (2007) Largest changes occurred in the Minnesota River ( Stats were considerably higher in the 1990 s than any previous period.) MN River Winter low-flow rates increasing at a higher rate than any other statistic. Related to an increase in Precipitation? Between 88-02, no significant change.

52 Ground Water Discharge A relatively new hydrologic pathway

53 Seven Mile Creek (Circa 1854) from Kuehner, (2004)

54 Subsurface or Tile Systems from Kuehner (2004) ~600 Miles of subsurface conveyance in 7-Mile Creek

55 Too Little Sediment? Class IV Toe slope scour resulting in undercut

56 Hydraulic Continuity Rosgen (1996)

57 Resistance to Flow Mannings n = (R 0.67 )(S 0.5 )/V Relative roughness = d/d 84 = f (V * D/V) Critical Shear Strength (τ c ) Erosion rate = ε = k (τ o τ c ) where: R = hydraulic radius = (A/2d + w), D = particle size, k = erodibility coefficient, f = Darcy-Weisbach resistance coefficient, τ o = boundary shear = γrs, V * = shear velocity

58 τo > τc

59 Excessive sediment supply & build-up of bed sediment

60 What Happened?

61

62 Stable Design?

63 the river is the carpenter of its own edifice (Leopold, 1994) Is there a relationship between channel form and drainage area?

64 Drainage Area? YES! There is a relationship between Channel Cross-sectional Area & Drainage Area?

65 Quasi-dynamic equilibrium For a given climate, geology, land use a channel X-SA will adjust to find quasidynamic equilibrium with respect to the contributing Drainage Area = BANKFULL.

66 USGS Streamflow Gage Lorenz, et al., 1997 Identify stage associated w/ channel forming flow Plot X-S area vs DA.

67 C r o s s - S e c t i o n a l A r e a ( S q F t ) Southwestern Minnesota Regional Curve y = x R 2 = from, Magner & Steffen (2000) Drainage Area (Sq Mi)

68 Red River Regional Hydraulic Geometry by Rosgen Type "C" "F" "E" Power ("F") Power ("C") Power ("E") y = x Cross-Sectional Area (Sq-Ft) y = x R 2 = R 2 = y = 2.585x R 2 = Drainage Area (Sq-Mi)

69 Bankfull Width Comparison B an kfu ll W id th Ohio curve y = 5.12x 0.5 Minnesota curve y = x Measured Bankful Width Ditches y = x Drainage Area (mi2) from Hansen et al., (2006)

70 Velocity and Sediment Transport

71 JD #8 Trapezoidal ώ = Ω /(γwd) = VS

72 JD #8 Natural Channel What happens when we decrease width-todepth ratio?

73 JD #8 Class V Is this a stable ditch?

74 JD #8 Trapezoidal Photo, Christner, jr

75 from Rosgen (1996) Channel Geometry

76 JD#8, Trapezoidal E le v a tio n (ft) from Christner, jr, Magner, & Brooks (2004) Width from River Left to Right (ft)

77 Low + High Flow JD #8 X-section Station 2000', Reach #2, JD#8, Swift Cty, MN JD#8, Natural Channel E le v a tio n (ft) from Christner, jr, Magner, & Brooks (2004) W idth from River Left to Right (ft)

78 Is Channel Form linked to TSS? WQ Violation?

79 Questions

80 From Brooks et al, 2003

81 From Brooks et al, 2003