CONCEPTS Conservational Channel Evolution and Pollutant Transport System

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1 CONCEPTS Conservational Channel Evolution and Pollutant Transport System Eddy J. Langendoen Watershed Physical Processes Research Unit National Sedimentation Laboratory USDA Agricultural Research Service Oxford, Mississippi

2 Input Data 2

3 Input data required by CONCEPTS n Geometries n Bank strength parameters- c, φ,φ b, γ s, τ c n Bed parameters- porosity, χ, bed layers, elevation of bedrock n Manning s n n Upstream and downstream boundary conditions 3

4 Input Data Hydraulics Data Requirements n Stream corridor geometry, i.e. cross section locations and profiles, and roughness n Hydraulic structure location, geometry, roughness, energy loss coefficients n Upstream discharge hydrograph n Downstream rating curve (optional) n Initial (base flow) conditions 4

5 Input Data Sediment Transport Data Requirements n Bed material stratigraphy, composition, and porosity n Percentage of fines (clay &silt) for which the bed can be assumed cohesive n Hiding coefficient n Critical shear stresses for erosion and deposition n Sediment load at upstream boundary n Percentage of bed control at the outlet 5

6 Input Data Streambank Erosion Data Requirements n Bank material properties Composition Unit weight Erodibility Shear strength n Bank roughness n Bank stability analysis options 6

7 Input Data Hydraulics Data Requirements n Stream corridor geometry, i.e. cross section locations and profiles, and roughness n Hydraulic structure location, geometry, roughness, energy loss coefficients n Upstream discharge hydrograph n Downstream rating curve (optional) n Initial (base flow) conditions 7

8 Geometries- How can we get it? n Many methods of terrestrial surveying exist, these include, but are not limited to: Tape, band or equivalent Leveling Total Station RTK Global Positioning System Terrestrial-based LIDAR Photogrammetry 8

9 Manning n Equation n The Manning equation calculates discharge as: 1 23 Q= K S = AR S n 9

10 Manning n n Many different equations. Most link n to Slope, Hydraulic Radius or Bed Particle Size n Descriptive methods. References: Chow (1959), USSCS (1975), USFHWA (1979), Coon (1998) n Cowan (1956) Component method.. n due to sediment size, surface irregularity, crosssectional variation, obstruction, vegetation, sinuosity n Photographic method Barnes (1967), Hicks and Mason (1999) 10

11 Manning n Equations Reference Jarrett (1984, 1990) Keulegan (1938) Limerinos (1970) Sauer (1990) Strickler (1923) Equation n= 0.32S R n= n = 0.035D R 0.16 R log D n= S R n= 0.039D

12 Input Data Hydraulics Data Requirements n Stream corridor geometry, i.e. cross section locations and profiles, and roughness n Hydraulic structure location, geometry, roughness, energy loss coefficients n Upstream discharge hydrograph n Downstream rating curve (optional) n Initial (base flow) conditions 12

13 Hydraulic Structures n 4 types of hydraulic structures (culvert, bridge crossing, drop structure, and generic structure) n Common parameters: name, river kilometer (km) Manning n, length (m), upstream and downstream inverts (m), upstream and downstream elevations of the structure above the streambed (m). 13

14 Hydraulic Structures- Culverts n Flow computation based on U.S. Federal Highway Administration's (1985) nomographs. n CONCEPTS can simulate the flow at box and pipe culverts. n Culverts require: USFHWA (1985) chart and scale number, entrance loss coefficient, number of culvert barrels in road crossing and their dimensions: diameter (m) for a pipe culvert, and span (m) and rise (m) for a box culvert. 14

15 Hydraulic Structures- Bridge Crossings n Shape of bridge crossing assumed to be trapezoidal with a horizontal bed. n Bridge crossings require: bottom width (m), side slope, total pier width (m), pier shape coefficient, pier loss coefficient. 15

16 Hydraulic Structures- Drop Structures n Cross-section of drop structure assumed to be trapezoidal with a horizontal bottom. n Bridge crossings require: bottom width (m), side slope, entrance loss coefficient. 16

17 Hydraulic Structures- Generic Structures n Any structure for which a rating curve is available. n Cross-section of walls of structure assumed to consist of linear elements. n Rating curve may comprise up to 4 segments, each segment being a power function. n Generic structures require: number of segments comprising walls of structure, bottom elevation (m) and slope of each segment, elevation of top of structure (m), details of rating curve, (number of segments, location of break points and coefficient and exponent of power function for each segment), 17

18 Input Data Hydraulics Data Requirements n Stream corridor geometry, i.e. cross section locations and profiles, and roughness n Hydraulic structure location, geometry, roughness, energy loss coefficients n Upstream discharge hydrograph n Downstream rating curve (optional) n Initial (base flow) conditions 18

19 Upstream and Downstream boundary conditions n Upstream (input) discharge n Downstream (output) rating curve (stagedischarge) n USGS has 7,292 stations, of which 4,200 are realtime n Computer database currently holds mean dailydischarge data for about 18,500 locations and more than 400,000 station-years of record, or more than 146 million individual mean dailydischarge values n Basic piece of data obtained at station is stage 19

20 What if there are no gaging stations nearby? n Interpolation between or extrapolation from gauging points on the same stream on the basis of drainage-area size. n Regional relations n Rational Method n Hydrological watershed models, e.g. variants of HEC-1 (including HEC-HMS, HEC-geoHMS), BASINS, SWAT, HSPF, the Watershed Modeling System, and USDA-ARS s AnnAGNPS 20

21 Input Data Streambank Erosion Data Requirements n Bank material properties Composition Unit weight Erodibility Shear strength n Bank roughness n Bank stability analysis options 21

22 Typical values for bank material parameters (from Selby, 1982). Description Friction angle φ' Cohesion c' (kpa ) Saturated unit weight (N/m 3 ) φ b (degrees) Gravel Angular sand Rounded sand Silt Stiff clay Soft clay

23 Cohesion and Friction Angle: Methods n in situ field techniques: borehole shear tester (BST) shear vane n laboratory techniques: shear box, triaxial shear test Shear Strength Envelope - Clay c' = 12.5, φ' = 16 degrees y = 0.296x n all (except shear vane) produce plots of shear stress vs normal stress Shear Stress at Failure (KPa) Normal Stress (KPa) 23

24 Flume methods of determining critical shear stress Device Annular Flume and Shaker Known Flow Conditions Field Tests Bedload Depth Range Armoring Erosion Rate Shear Stress Range Yes No No 0-2 mm Yes No 0-1 Pa SEDFlume Yes Yes No 0-1 m No Yes 0-10 Pa SEDFlume w/ Trap Channel Oscillatory Flume Yes No 1 Yes 0-1 m No Yes 0-10 Pa Yes Yes No 0-1 m Some Yes 0-10 Pa 1 from Gailani, personal communication,

25 In Situ Jet test device for determining critical shear stress n n n n n Developed by the Agricultural Research Service (Hanson, 1990). Based on knowledge of hydraulic characteristics of a submerged jet and the characteristics of soil-material erodibility. Apparatus: pump, adjustable head tank, jet submergence tank, jet nozzle, delivery tube, and point gage. The stress range = Pa. Maximum scour measurements are taken at five to ten minute intervals over a period of 60 to 120 minutes. 25

26 Materials properties (Particle sizes, Unit weight and Porosity) n Particle size distributions.. method: n dry sample either in air at room temperature or with a warming device not to exceed 60 C in temperature. n clumps of particles broken up using mortar and rubbercoated pestle, before weighing the sample. n sample then washed over a 2.0 mm sieve, dried and reweighed. n required minimum mass of soil retained on the 2.0 mm sieve is dependent on the maximum particle size: gravels > 4 kg, sands = kg, silts and clays = kg. 26

27 Materials properties (Particle sizes, Unit weight and Porosity) n Particle size distributions.. method: n separate retained portion into a series of fractions using the 75 mm, 50 mm, 37.5 mm, 25.0 mm, 19.0 mm, 9.5 mm, 4.75 mm and 2.0 mm sieves. n remainder ( kg) prepared for hydrometer analysis. n hydrometer readings should be taken at 2, 5, 15, 30, 60, 250, and 1440 minutes. n transfer suspension to a 75-mm sieve and washed until the wash water is clear. diameter of a particle is calculated according to Stokes law. 27

28 Materials properties (Particle sizes, Unit weight and Porosity) n Unit weight, γ s n defined as ratio of the weight of soil solids, W s to the total volume of the soil, V. n found by drying a sample of known weight and volume for over 16 hours at 110 ºC, before reweighing. 28

29 Materials properties (Particle sizes, Unit weight and Porosity) n Porosity, n n defined as the volume of air- and water-filled voids in a soil divided by the total volume of the soil. n Rearranging, this can be shown to equal 1 ρ ρ b m where ρ b is bulk density and ρ m is particle density (assumed to be equal to 2600 kg m -3 for organic materials, 2650 kg m -3 for granular materials and 2700 kg m -3 for clays). n Therefore, porosity can be calculated by subtracting laboratory values of bulk density divided by one of these constants from 1. 29

30 Typical porosity and unit weight values for a range of sediments. Unit weight, γ s, knm -3 Porosity, n Soil Type Max. Min. Max. Min. Clay (30-50% clay sizes) Skip-graded silty clay with stones or rock fragments Uniform, inorganic silt Silty sand Clean uniform sand (fine or medium) Clean, fine to coarse sand Micaceous sand Sandy or silty clay Silty sand and gravel Well-graded gravel, sand, silt, and clay mixture

31 INPUT FILES 31

32 Types of Input Files n CONCEPTS requires two types of input files to be created in order to run. XML-based input file containing physical data, channel models, and run data (*.concepts) Inflow files 32

33 Input Files XML data file 33

34 Input Files Inflow Files n Discharges (water and sediment by size class) inputted into the upstream end of the reach and tributaries. n Includes: all discharge records (in m 3 s -1 ), date and time, identifier signifying the start of a storm event, the end of a storm event or between storm events for each record. 34

35 Input Files Inflow Files (cont.) 35

36 Input Files Inflow Files (cont.) 36

37 OUTPUT DATA 37

38 Output Data. n CONCEPTS creates three types of output: output at a certain cross-section and for a certain runoff event, time-series output at a chosen cross-section, and output for a certain runoff event along a section of the modeling reach (profiles). 38

39 Output at a Certain Location and for a Certain Runoff Event n To request data for a chosen cross-section and runoff event, user has to: enter number of locations at which output is requested. for each location, user must enter: n type of data required, n location of required cross-section within modeling reach, n dates of runoff events for which output is requested, repeated for however many output cross-sections are required. 39

40 Output at a Location and a Runoff Event (Parameters) Outputted parameter Value peak discharge 1 peak flow depth 2 peak stage 4 peak friction slope 8 sediment yield 16 cumulative sediment yield 32 change in bed elevation 64 cumulative change in bed elevation

41 Output at a Location and a Runoff Event (Parameters cont.) Outputted parameter Value lateral erosion 256 cumulative lateral erosion 512 cross-sectional geometry 1,024 in-bank top and bottom width 2,048 bank height 4,096 characteristic particle sizes 16,384 particle size distribution 32,768 41

42 Time-Series Output at a Certain Location n n CONCEPTS checks if time falls between start and end time of all requested time series. When model time is within time series boundaries, the requested parameters are printed. To request output at a certain cross-section over a period of time, the user has to: enter number of locations at which output is requested. for each location, user must enter: n type of data required, n the location of the required cross-section within the modeling reach, n the start and end dates of the time series, repeated for however many output cross-sections are required. 42

43 Time-Series Output at a Location (Parameters) Outputted parameter Value discharge 1 velocity 2 flow depth 4 stage 8 flow area 16 flow top width 32 wetted perimeter 64 hydraulic radius 128 conveyance

44 Time-Series Output at a Location (Parameters cont.) Outputted parameter Value friction slope 512 energy head 1,024 Froude number 2,048 bed shear stress 4,096 sediment discharge (silt,sand,gravel,total) 8,192 cumulative sediment yield (silt,sand,gravel,total) 16,384 cumulative change in bed elevation 32,768 thalweg elevation 65,536 cumulative lateral erosion 131,072 44

45 Time-Series Output at a Location (Parameters cont.) Outputted parameter Value factor of safety 524,288 apparent cohesion 1,048,576 pore-water force 2,097,152 matric suction force 4,194,304 weight of failure block 8,388,608 weight of water on the bank 16,777,216 horizontal component of confining force 33,554,432 groundwater elevation 67,108,864 location of bank top 134,217,728 45

46 Output for a Certain Runoff Event along a Section of the Modeling Reach n In order to request output for a certain runoff event along a profile, the user must enter: number of profiles at which output is requested, type of data, locations of first and last cross-section of the profile are entered, dates of the storm events for which output is requested for that particular profile, n repeated for however many output profiles are required. 46

47 Output for Runoff Events along a Profile (Parameters) Outputted parameter Value peak discharge 1 peak stage 2 thalweg elevation 4 cumulative change in bed elevation 8 in-bank top width 16 bank height 32 sediment yield (silt,sand,gravel,total) 64 characteristic particle sizes

Open Channel Flow Part 2. Ch 10 Young, notes, handouts

Open Channel Flow Part 2. Ch 10 Young, notes, handouts Open Channel Flow Part 2 Ch 10 Young, notes, handouts Uniform Channel Flow Many situations have a good approximation d(v,y,q)/dx=0 Uniform flow Look at extended Bernoulli equation Friction slope exactly