6.12. jules_rivers.nml

This file sets the river routing options. It contains two namelists called JULES_RIVERS and JULES_OVERBANK.

Note

The river routing code in JULES is still in development. Users should ensure that results are as expected, and provide feedback where deficiencies are identified.

6.12.1. JULES_RIVERS namelist members

JULES_RIVERS::l_rivers

Type:logical Default:F

Switch for enabling river routing.

TRUE

Use the river routing algorithm specified by rivers_type to route runoff along river pathways.

FALSE

No river routing.

JULES_RIVERS::rivers_type

Type:character Default:rfm

Switch to select the river routing algorithm to use for river routing.

rfm

Use a standalone JULES implementation of the RFM kinematic wave model (see Dadson and Bell (2010), Bell et al. (2007)).

trip

Use a standalone JULES implementation of the linear TRIP model (see Oki et al. (1999)).

JULES_RIVERS::rivers_timestep

Type:integer Permitted:> 0 Default:-32768

The number of model timesteps per routing timestep.

For example, rivers_timestep = 5 means that runoff will be accumulated for 5 model timesteps before being routed on the 5th timestep.

Warning

The river routing parameter values can be highly dependent on model resolution, so care is required by the user to ensure that appropriate values are selected, tested and adjusted as required.

Suggested values for global and high-resolution runs are listed below, however these should be treated as a starting point.

Values for some typical configurations are included in the jules_riversparm module.

RFM parameters - used if rivers_type = rfm

JULES_RIVERS::cland

Type:real Default:0.2 Suggested:0.2 (global), 0.4 (high-resolution)

The land wave speed (m s^-1). See Bell et al. (2007).

JULES_RIVERS::criver

Type:real Default:0.62 Suggested:0.62 (global), 0.5 (high-resolution)

The river wave speed (m s^-1). See Bell et al. (2007).

JULES_RIVERS::cbland

Type:real Permitted:<= cland Default:0.1 Suggested:0.1 (global), 0.05 (high-resolution)

The subsurface land wave speed (m s^-1). See Bell et al. (2007).

JULES_RIVERS::cbriver

Type:real Permitted:<= criver Default:0.15 Suggested:0.15 (global), 0.05 (high-resolution)

The subsurface river wave speed (m s^-1). See Bell et al. (2007).

JULES_RIVERS::retl

Type:real Permitted:0-1 Default:0.0

The (resolution dependent) land return flow fraction. See Bell et al. (2007).

JULES_RIVERS::retr

Type:real Permitted:0-1 Default:0.005 Suggested:0.005 (global), 0.005 (high-resolution)

The (resolution dependent) river return flow fraction. See Bell et al. (2007).

JULES_RIVERS::a_thresh

Type:integer Default:1 Suggested:1 (global), ~10 (high-resolution)

The threshold drainage area (specified in number of cells) draining to a gridbox, above which the gridbox is considered to be a river point. This is resolution dependent.

Remaining points are treated as land (drainage area = 0) or sea (drainage area < 0). See Bell et al. (2007).

JULES_RIVERS::runoff_factor

Type:real Default:1.0

It is highly recommended that this is set to 1.0 (i.e. no runoff adjustment).

TRIP parameters - used if rivers_type = trip

JULES_RIVERS::rivers_speed

Type:real Default:0.4

The effective river velocity (m s^-1). See Oki et al. (1999).

JULES_RIVERS::rivers_meander

Type:real Default:1.4

The ratio of the actual to calculated river lengths in a river routing gridbox. See Oki et al. (1999).

JULES_RIVERS::l_riv_overbank

Type:logical Default:F

Switch for enabling river overbank inundation. Only used if l_rivers is TRUE. Default setting is FALSE.

TRUE

Calculate an overbank inundation gridbox fraction (frac_fplain_lp).

FALSE

No overbank inundation calculations

See also

References:

• Bell, V.A. et al. (2007) Development of a high resolution grid-based river flow model for use with regional climate model output. Hydrology and Earth System Sciences. 11 532-549
• Dadson, S.J. and Bell, V.A. (2010) Comparison of Grid-2-Grid and TRIP runoff routing schemes. Centre for Ecology & Hydrology Internal Report http://nora.nerc.ac.uk/10890/1/dadson_etal_2010_g2gtrip.pdf
• Dadson S.J. et al. (2011) Evaluation of a grid-based river flow model configured for use in a regional climate model. Journal of Hydrology. 411 238-250
• Falloon, P.D. et al (2007) New global river routing scheme in the Unified Model. Hadley Centre Technical Note 72, available from the Met Office Library.
• Jones R., Dadson, S. and Bell, V.A. (2007) Report on European grid-based river-flow modelling for application to Regional Climate Models. Met Office Hadley Centre deliverable report.
• Oki, T., et al (1999) Assessment of annual runoff from land surface models using Total Runoff Integrating Pathways (TRIP). Journal of the Meteorological Society of Japan. 77 235-255

6.12.2. JULES_OVERBANK namelist members

Warning

The overbank inundation parameter values can be highly dependent on model resolution, so care is required by the user to ensure that appropriate values are selected, tested and adjusted as required.

Suggested values for global and high-resolution runs are listed below, however these should be treated as a starting point only.

JULES_OVERBANK::l_riv_hypsometry

Type:logical Default:F

Switch for enabling use of a hypsometric integral calculation.

TRUE

Calculate inundated area from a hypsometric integral (recommended).

FALSE

Estimate inundated area from river width, ignoring topography (only to be used for testing).

River width allometry (used if l_riv_hypsometry is false or use_rosgen is true)

Allometry is: (WIDTH in m) = riv_a * ( (SURFACE RIVER INFLOW in m3 s^-1) ** riv_b) (Leopold & Maddock 1953:eqn1)

JULES_OVERBANK::riv_a

Type:real Default:7.20 Permitted:>=0 and <=(1/riv_c) Suggested:7.20 (global, from Andreadis et al. 2013)

Coefficient in the allometry for river width (units are (m / ((m3/s)^riv_b)), i.e. dependent on the value of riv_b)

JULES_OVERBANK::riv_b

Type:real Default:0.50 Permitted:>=0 and <=(1-riv_f) Suggested:0.50 (global, from Andreadis et al. 2013)

Exponent in the allometry for river width (dimensionless)

River depth allometry (used if l_riv_hypsometry is true or use_rosgen is true)

Allometry is: (DEPTH in m) = riv_c * ( (SURFACE RIVER INFLOW in m3 s^-1) ** riv_f) (Leopold & Maddock 1953:eqn2)

JULES_OVERBANK::riv_c

Type:real Default:0.27 Permitted:>=0 and <=(1/riv_a) Suggested:0.27 (global, from Andreadis et al. 2013)

Coefficient in the allometry for river depth (units are (m / ((m3/s)^riv_f)), i.e. dependent on the value of riv_f)

JULES_OVERBANK::riv_f

Type:real Default:0.30 Permitted:>=0 and <=(1-riv_b) Suggested:0.30 (global, from Andreadis et al. 2013)

Exponent in the allometry for river depth (dimensionless)

Rosgen stream classification parameters describing river channel morphology (Rosgen 1994)

JULES_OVERBANK::use_rosgen

Type:logical Default:F

Switch for applying the Rosgen entrenchment ratio approach

TRUE

When inflow rates are lower than bankfull flow, river width is calculated from the riv_a / riv_b allometry. However, when higher than bankfull flow, river width is constrained so that when river depth = 2 x bankfull depth then width = ent_ratio * bankfull width.

FALSE

River width follows the allometry specified above whatever the inflow rate.

Bankfull flow allometry (used if use_rosgen is true)

Allometry is: (BANKFULL DISCHARGE RATE in m3 s^-1) = coef_b * ( (CONTRIBUTING AREA in km2) ** exp_c ) (see e.g. Andreadis et al. 2013)

JULES_OVERBANK::coef_b

Type:real Default:0.08

Coefficient in the allometry for bankfull flow

JULES_OVERBANK::exp_c

Type:real Default:0.95

Exponent in the allometry for bankfull flow

JULES_OVERBANK::ent_ratio

Type:real Default:4.0

The Rosgen entrenchment ratio (single value for all water courses in the simulation): when river depth = 2 x bankfull depth then width = ent_ratio * bankfull width (i.e. ent_ratio can be used to specify how wide floodplains are allowed to be).

See also

References:

• Andreadis KM, Schumann GJ & Pavelsky T (2013). A simple global river bankfull width and depth database. Water Resources Research 49:7164-7168
• Leopold LB & Maddock T (1953). The Hydraulic Geometry of Stream Channels and Some Physiographic Implications. United States Geological Survey Professional Papers 252:1-57
• Rosgen DL (1994). A classification of natural rivers. Catena 22:169-199.