CES Section
  • 16 Aug 2022
  • 4 Minutes to read
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CES Section

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CES (Conveyance Estimation System) Section offers an alternative method of calculating conveyance for a River Section, using the Depth-Integrated Reynolds-Averaged Navier-Stokes Method.


Field in Data Entry Form


Name in Datafile

Section Label


Node label for cross section

First Spill


First spill label

Second Spill


Second spill label

Distance to Next


Distance to next cross section (a zero specifies the end of the reach) (m)

Reach Slope


slope estimate (m/m)

Default Sinuosity


default sinuosity (m/m)



Number of ensuing data lines



Cross chainage (m)



Elevation of bed (mAD)

Bank Marker


One of the following:

  • 'LI' to indicate a left bank on the inside of a bend
  • 'RO' to indicate a right bank on the outside of a band
  • 'LO' to indicate a left bank on the outside of a bend
  • 'RI' to indicate a right bank on the inside of a bend
  • 'LS' to indicate a left bank on a straight
  • 'RS' to indicate a right bank on a straight
  • ' ' (blank) if the current point is not a bank top



Sinuosity of the river between the current left bank and the next right bank, if different from the default sinuosity.  Only used if there is a left bank marker on the same line



The words LEFT', 'RIGHT', or 'BED' specifying the left bank top, right bank top and thalweg. These are for plotting purposes in the Flood Modeller UI only, and are not used in the calculation. Defaults are to the first, last and minimum levels specified respectively. A 'D' marker may also be used in this field to specify the lateral limits of dredging for the mobile bed sediment transport module, 1D Sediment Transport solver



Easting of point



Northing of point



Number of ensuing roughness zone lines

Zone Name


Roughness zone name



Roughness in zone


  1. The bank markers must appear in pairs separated only by lines without bank markers, as follows:
  • LI must be followed by RO
  • LO must be followed by RI
  • LS must be followed by RS
  • RO must be preceded by LI
  • RI must be preceded by LO
  • RS must be preceded by LS

Theory and Guidance

The CES Section offers a new, alternative method of calculating conveyance for a River Section. The approach uses the Depth-Integrated Reynolds-Averaged Navier-Stokes Method.

For advice on setting up CES sections e.g. positioning of bank markers, and the advanced options that are available, please refer to Conveyance User Manual.

Conveyance is calculated at a given water level through calculating the lateral unit flow rate q (m2s-1) distribution, integrating q across the section to determine the total flow rate Q (m3s-1 ) and then dividing by the square root of the longitudinal slope S to obtain the total section conveyance K (m3s-1) i.e.



Here, S is approximated from the reach-averaged longitudinal bed slope. The unit flow rate distribution is based on the depth-integrated Reynolds-Averaged Navier-Stokes [RANS] equation for flow in the streamwise direction, with empirical closure for the estimation of certain depth-integrated stresses, i.e.



1.0 = s (inbank)

1.0 £ s £ 1.015 (overbank)



s > 1.0 (inbank)

s > 1.015 (overbank)


g is the gravitational acceleration (m.s-2)

H is the local depth normal to the channel bed (m)

h is the surface water level (m)

y is the lateral distance across the channel (m)

b is the coefficient to account for influence of local bedslope on the bed shear stress

s is the reach-averaged sinuosity

For solution of Equation (2), the cross-section is discretised laterally (Figure 1) into 100 divisions (default value) and there are 25 (default value) depths for solution.

Equation (2) has four calibration coefficients: the local friction factor f, the dimensionless eddy viscosity l , the secondary flow parameter G and the coefficient of meandering Cuv. For detailed descriptions of the models for estimating these calibration coefficients see DEFRA/EA (2003, 2004a & 2004b)[1]. Variation of the calculation parameters is permissible. Advice on how these parameters may be varied to optimise model predictions is available in DEFRA/EA (2004b).

RiverNodesimagesCES001.gifFigure 1: Cross-section discretisation

 [1] DEFRA/EA, 2003, Reducing Uncertainty in River Flood Conveyance, Interim Report 2: Review of Methods for Estimating Conveyance, Project W5A- 057, HR Wallingford Ltd., United Kingdom.

DEFRA/EA, 2004, Reducing Uncertainty in River Flood Conveyance, Interim Report 3:Further Validation of stage-discharge prediction, application within Flood Modeller and Development and Statement of Advice on Uncertainty, Project W5A- 057, HR Wallingford Ltd., United Kingdom.

EA/DEFRA, 2004b, Reducing Uncertainty in River Flood Conveyance: Conveyance Manual, Project W5A- 057, HR Wallingford Ltd., United Kingdom.

Datafile Format

General Parameters

The general parameters section of the DAT file contains an absolute path to the roughness file:

Line 1 - Title - Up to 40 characters

Line 2 - #REVISION#1

Line 3 - Nnodes Frmin Frmax Dmin Stol

Line 4 - T Qtol Htol Θ P α η

Line 5 - RAD FILE

Line 6 - Absolute path to roughness file


CES Data

Items in square brackets are optional. Items in capitals are keywords.
Line 1 - RIVER [comment]


Line 3 - Label1 [Label2] [Label3] [Lateral 1] [Lateral 2] [Lateral 3] [Lateral 4]

Line 4 - dx [yshift] slope def_sinuosity

Line 5 - n1

Line 6 to Line 5+n1- c z [bank] [sinuosity] [lrb] [easting] [northing]

Line 6+n1- n2

Line 7+n 1 to Line 6+ n+ n- c rz



  1. Line 3 is in fields of either 8 or 12 characters, depending on a parameter set globally for the model. Lines 4 and 5 are in fields of 10 characters. The section data lines are F10.0, F10.0, A10, F10.0, A10, F10.0, F10.0. The roughness zone lines are F10.0, A.

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