Sediment Boundary Conditions

All upstream boundaries must be specified. Either GTBDY (sediment transport rate against time), CTBDY (sediment concentration against time) or QCBDY (sediment rating curve) units may be used. The boundary data are contained in the mobile bed module datafile ('filename.sed'). They can be specified in any order in the data file and may use any combination of GTBDY, CTBDY or QCBDY units. An example of the structure of this section of the file is shown in Figure 3.

Datafile Format - sediment boundary data block

Line 1                             keyword 'GTBDY' or 'CTBDY' or 'QCBDY'                         [comment]

Line 2                             Label

Line 3                             n1, [tm]

Line 4 to Line 3+n1        Gi, ti     for GTBDY

                                      Ci, ti     for CTBDY

                                      Qi, Ci    for QCBDY

Line 4+n1                      sizedist= 'BED' or 'NEW'

(Input files for earlier versions of 1D Sediment Transport Solver may not include this line. If it is omitted then 'BED' is assumed.)

The following lines are only required if sizedist=NEW

Line 5+nto Line 4+n+nsed P_i

Where

Label = node label at boundary

n1 = number of ensuing data pairs

tm = optional keyword or value for units of time in following data set. Can be any numerical multiplier or one of the following: seconds (default), minutes, hours, days, weeks, months (=30 days) or years.

G_i= sediment transport rate (kg/s) corresponding to time, t(for GTBDY units)

C_i= sediment concentration (ppm) corresponding to time, t(for CTBDY units)

t_i= time (in units of t)

sizedist = keyword setting the size distribution for sediment inflows. Enter:

NEW if new distribution is to be used

BED to use default distribution given in General Data.

P_i= new grading data for sediment inflow (only required if sizedist=NEW)

General

For QCBDY boundaries the data format is pairs of flow rate (m3/s) and concentration (ppm). The flow rates must encompass the flows calculated during the simulation.

For GTBDY and CTBDY boundaries it is important that the start and end times specified encompass the entire computation time space for the model run.

The data pairs specified need not coincide with computational time steps. However, when digitising data to capture the shape of the graph, it is important to bear in mind that linear interpolation is used between data points, and therefore more points may be needed where the curvature is high.

Concentrations (C) in ppm by weight are converted to transport rates (G) in m/s using the following equation:

Where

Q = water flow rate in m/s

s = specific gravity of first sediment size fraction