Overland and Channel Routing in the Distributed Model

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Overland and Channel Routing in the Distributed Model

Lecture 4a

Yu Zhang

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Outline• Conceptual model

• Parameter estimation– Connectivity– Slopes– Channel hydraulic properties

• Local customization steps

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Overland flow routed independently for each

hillslope

(adapted from Chow et al., 1988)

HRAP Cell (~ 4 km x 4 km) Uniform, conceptual hillslopes within a modeling unit are assumed

• Drainage density illustrated is ~1.1 km/km2• Number of hillslopes depends on drainage density

Conceptual channel provides cell-

to-cell link

Overland flow routed independently for each

hillslope

(adapted from Chow et al., 1988)

HRAP Cell (~ 4 km x 4 km) Uniform, conceptual hillslopes within a modeling unit are assumed

• Drainage density illustrated is ~1.1 km/km2• Number of hillslopes depends on drainage density

Conceptual channel provides cell-

to-cell link

Real HRAP Cell

Hillslope model

Cell-to-cell channel routing

Routing Model

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Fast runoff components• Surface• Direct• Impervious

Slow runoff components• Interflow• Supplemental baseflow• Primary baseflow

Hillslope routing

Channel routing

Separate Treatment of Fast and Slow Runoff

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ABRFC ~33,000 cells

MARFC ~14,000 cells

• OHD delivers baseline HRAP resolution connectivity, channel slope, and hillslope slope grids for each CONUS RFC

• HRAP cell-to-cell connectivity and slope grids are derived from higher resolution DEM data.

HRAP Cell-to-cell Connectivity Examples

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Representative Slopes Are Extracted from Higher Resolution DEMS(North Fork of the American River (850 km2))

Slopes from 30-m DEM

Hillslope Slope (1/2 HRAP Resolution)Average = 0.15Slopes of all DEM cells within the HRAP pixel are averaged.

Main Channel Slope (1/2 HRAP Resolution)Average = 0.06Channel slopes are assigned based on a representative channel with the closest drainage area.

Local Channel Slope (1/2 HRAP Resolution)Average = 0.11

Slope (m/m)

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A

B

Main Channel Slope vs. Local Channel Slope

(1) Slopes of each stream segment are calculated from the DEM

(2) Model cell slopes are assigned from representative segments that most closely match either the cell’s cumulative or local drainage area. In this case, the slope of segment A is taken as the ‘main’ channel slope and slope of segment B is taken as the ‘local’ channel slope.

Segment Slopes (m/m)

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Channel Routing Model• Uses implicit finite difference solution technique• Solution requires a unique, single-valued

relationship between cross-sectional area (A) and flow (Q) in each grid cell (Q=q0Aqm)

• Distributed values for the parameters q0 and qm in this relationship are derived by using – USGS flow measurement data at selected points– Connectivity/slope data– Geomorphologic relationships

• Training on techniques to derive spatially distributed parameter grids is provided in this workshop

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Kinematic Wave Equations Solved by HL-RDHM:Hillslope FlowKoren et al. (2004)

sh Rx

qL

t

h

3

53

52hqh

n

SDq s

h

h hLx 0

q = discharge per unit area of hillslopeh = average overland flow depthRs = fast runoff from water balanceSh = hillslope slopenh = hillslope roughnessD = drainage densityLh = hillslope length

(continuity) (momentum)

Conceptual Hillslopes (higher D = more hillslopes and faster response)

DLh 2

1

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Kinematic Wave Equations Solved by HL-RDHM:Channel FlowKoren et al. (2004)

‘Kinematic’ wave solution assumes slope dominates all other forces (e.g. inertial (rapid changes), pressure, wind, tides)

c

cgL L

fRq

x

Q

t

Ah

cLx 0 mqAqQ 0

(continuity) (momentum)

Q = channel dischargeA = channel cross-sectional areaqLh = overland flow rate at the hillslope outletRg = slow runoff component from the water balanceFc = grid cell areaLc = channel length within a cell

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Kinematic Wave vs. Unit Hydrograph

• If (qm != 1), channel velocity will vary with flow level (linear superposition does not apply).• Typically qm > 1, resulting in faster flood propagation at high flows.•If qm == 1, channel flow behavior would be similar to a unit hydrograph in the case of uniform runoff (overland flow velocity can still be flow dependent).

0

200

400

600

800

1000

1200

1400

0 20 40 60 80

Time (hours)

Flo

w (

cms)

KW 12.7

KW 25.4

KW 50.8mm

2 x KW 25.4 mm

0.5 * KW 25.4

UG Peak Time

Smaller flood delayed

Larger flood accelerated

Treating KW 25.4 like UG

qmAQ q0

Same q0,qm

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Two Simple Channel-Flood Plain Models areAvailable in HL-RDHM

• The ‘Rating Curve’ model estimates the parameters q0 and qm directly for each model cell using hydraulic measurements at an outlet gauging station, cell drainage areas, and geomorphologic relationships. • The ‘Channel shape’ method assumes a simple parabolic channel geometry and uses outlet hydraulic measurements, cell drainage areas, slopes, the Chezy-Manning equation, and geomorphologic relationships to estimate q0 and qm for each cell. • Both models have produced good results in our applications.

q0 qm

qmAQ q0

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‘Channel Shape’ Model

• Assume simple relationship between top width (B) and depth (H)

• Solve for and at a USGS gauge using streamflow measurement data

• Use geomorphologic relationships to derive spatially variable a values (see Koren, 2004 for details)

• Compute q0 and qm as a function of and , channel slope (Sc) and channel roughness (nc)

B H

= 1

< 1

> 1

)1(32

0 )1(

c

c

n

Sq

13

5

mq

= 0

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‘Rating Curve’ Model

• Solve for q0 and qm at a USGS gauge using streamflow measurement data

• Use geomorphologic relationships to derive spatially variable a values (see Koren, 2004 for details)

qmAQ q0

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WATTS (1645 km2) KNSO2 (285 km2)

CAVESP (90 km2) SPRINGT (37 km2)

Model predicted relationships (p) at points upstream from TALO2 (2484 km2) compared with local fits (l)

ModelValidation

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Routing Parameter Grids

Default grid values:rutpix_ALPHC: -1 (nodata)rutpix_BETAC: 1rutpix_DS: 2.5rutpix_Q0CHN: -1 (nodata)rutpix_QMCHN: 1.333rutpix_ROUGC: -1 (nodata)rutpix_ROUGH: 0.15

Rutpix7 = ‘channel shape’Rutpix9 = ‘rating curve’

No. Grid Name Description Required for 1 rutpix_SLOPC channel slope (Sc) Rutpix7 2 rutpix_ROUGC channel roughness

(Manning’s n, nc) Rutpix7

3 rutpix_BETAC channel shape parameter ( in B = H)

Rutpix7

4 rutpix_ALPHC channel width parameter ( in B = H)

Rutpix7

5 rutpix_SLOPH hillslope slope (Sh) Rutpix7, rutpix9 6 rutpix_DS drainage density (D) Rutpix7, rutpix9 7 rutpix_ROUGH hillslope roughness (nh) Rutpix7, rutpix9 8 rutpix_Q0CHN q0 in Q = q0A

qm Rutpix9 9 rutpix_QMCHN qm in Q = q0A

qm Rutpix9

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Routing Parameter Customization Procedures (User Manual Chapter 9)

• Determine best HRAP cell to represent basin outlet (XDMS)

• Add outlet to connectivity file header• Adjust cell areas so the total drainage area

matches USGS area (cellarea program)• Download measurement data from USGS NWIS

site• (optional) Use preprocess.R to parse USGS flow

measurement data for multiple stations into separate files

• Use outletmeas_manual.R to analyze station data

• Use genpar utility program to generate grids

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2258 km2

285 km2

795 km2

HRAP Cell Connectivity

Model Resolution and Basin Size Considerations

Percent errors in representing basins with 4 km resolution pixels.• Open squares represent errors due to resolution only. • Black diamonds represent errors due to resolution and connectivity.• We correct for these errors by adjusting cell areas in the model so that the sum of the model cell areas matches the USGS reported area at the basin outlet.

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1 TIFM7 Elk River near Tiff City Mo 22582 POWEL Big Sugar Creek near Powell MO 3653 LANAG Indian Creek near Lanagan MO 619

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User must choose which cell is the best outlet for this basin.

Gauge Name Area (km2)ID

4 km resolution does not allow accurate selection of an outlet for this subbasin because

HRAP vs. ½ HRAP Implementation

2 km resolution allows more accurate delineation

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Connectivity File Example

Change this number when adding outlets

User defined header lines

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Outletmeas_manual.R: Additional Plots

Q vs. A for Two Methods

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R Scripts Provided to Assist with Flow Measurement Analysis

• Outletmeas_manual.R automatically generates several plots and computes reqressions• User can specify plotting and regression weight options• Derived parameters are saved to a file for later use

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Outletmeas_manual.R User Options

#---(1)--- input file namefile.list<-"/fs/hsmb5/hydro/users/sreed/flow_measurements/dmip2/talo2meas3_29_07.d"

#---(2)--- user specified weight exponent for regressionQwt.qa<-1 # for Q-AQwt.ab<-1 # for A-BQwt.n <-1 # for Manning's n

#---(3)--- User specified relative weights for each of the USGS data quality flagsws<-c(1,1,1,1,1)

#---------------------------------# Code Description # ---------------------------------# E Excellent the data is within 2% (percent) of the actual flow# G Good the data is within 5% (percent) of the actual flow# F Fair the data is within 8% (percent) of the actual flow# P Poor the data are not within 8% (percent) of the actual flow# -1 Missing# The ws vector is ordered as above c(E,G,F,P,-1)

#---(4)--- graph optionsplot_quality=Tnew_graphics=T

#---(5)--- info for the channel shape methodslope=0.002

#reread_data=TRUE

#--- (6)--- output file namesfile.out<-"param.final.d"

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Genpar Input Deck

#genpar.card#enter the connectivity file nameconnectivity = /fs/hsmb5/hydro/users/zhangy/RDHM/Genpar/sequence/abrfc_var_adj.con#specify an input location for parameter gridsinput-path = /fs/hsmb5/hydro/rms/parameterslx/abrfc#specificy an output locationoutput-path = /fs/hsmb5/hydro/users/zhangy/RDHM/Genpar/output#replace/update the existing grid or output the grid to the output-path, true or false#overwrite-existing-grid = false##create a new grid instead of modify existing grid, the boundary in this# case is the boundary of all selected basins, true or falsecreate-new-grid = true##if the create-new-grid is true, the grid will be created in this window.#if this window is not consistent with the window from the connectivity,#the windows are combined into a big window that contains both subwindows.#window-in-hrap = 480 505 298 306 ## Name of the parameter to be created, available names are:# slopc rougc betac alphc sloph ds rough Q0CHN QMCHM # They are case insensitive#genpar-id = slopc#genpar-id = rougc#genpar-id = alphc#the next line specifies the parameter for which values will be generatedgenpar-id = q0chn#genpar-id = qmchn#next line is an example input information for q0chn grid generationgenpar-data = TALO2 0.31 1.2 Table 9.3 tells you what to

put here

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No. genpar-id Arguments Comments

1 SLOPC 0.178 1.23 Use defaults

2 ROUGC no 0.272 -0.00011 The user should specify the first argument and use defaults for arguments 2 and 3.

3 BETAC

Betac

4 ALPHC

-1 Ao alphac Enter -1 for the first argument since it is no longer used. Ao is a representative

cross sectional area at the outlet.

5 SLOPH

constant Typically, this option is not needed since reasonable values of SLOPH can be derived from the DEM.

6 DS

Constant

7 ROUGH

Constant

8 Q0CHN q0chn qmchn

9 QMCHN qmchn

Required Arguments for Grid Generation

Condensed Table 9.3