This readme file describes the functionality introduced in the NIWA Sedprocs Branch of the Delft3D source code. Richard Measures, NIWA, Richard.Measures@niwa.co.nz 1. Additional Sediment Transport Formula for gravel bed rivers -------------------------------------------------------------- Three new sediment transport formula have been introduced. These formulas are included as additional options to the formula already described in the manual (section 11.5). The additional formula added are: -> Wilcock and Crowe (2003, "Surface based transport for mixed size sediment", Journal of Hydraulic Engineering) -> Modified Wilcock and Crowe (Gaeuman et al, 2009, "Predicting fractional bed load transport rates: Application of the Wilcock-Crowe equations to a regulated gravel bed river" Water Resources Research) -> Gaeuman et al (2009, "Predicting fractional bed load transport rates: Application of the Wilcock-Crowe equations to a regulated gravel bed river" Water Resources Research) These formula can be accessed using the sediment transport input file as described in section B.9.3 of the manual. The input parameters are: Formula IFORM Input Parameters ---------------------------------------------------------------------------------- Wilcock and Crowe 16 calibration coefficient alpha (default=1) Modified Wilcock and Crowe 17 Theta c0 (default = 0.21), Alpha 0 (default = 0.33) Gaeuman et al 18 Theta c0 (default = 0.03), Alpha 0 (default = 0.30) Additional optional output parameters added to trim file. Outputs can be turned on by addition of keywords to *.mor file in the same way as other existing optional outputs (e.g. MudFrac): DgSD geometric standard deviation of surface grain size mixture (all fractions) SandFrac Sand Fraction (required by Wilcock Crowe ST formula) - Fraction of surface composition consisting of sand sized particles. Note: This has now been implemented in main D3D trunk. 2. Limiting slope bank erosion mechanism ---------------------------------------- A slope based bank erosion mechanism has been introduced (possibly similar to the existing avalan subroutine?? undocumented part of the code) but better in several ways (no directional bias due to calculation direction, no (? or certainly less) directional bias due to grid orientation. Handles multiple size fractions.) This option is turned on using the keyword "Repose" in the [morphology] part of the .mor file (B.9.2 in manual). The Repose keyword specifies the repose gradient (in m/m) above which slope failure will occur, for example Repose = 1 specifies a slope of 45degrees. For this erosion mechanism to be effective in the model: grid size [m] < (water depth at bank [m] - SedThr [m]) / ((2^0.5) * Repose [m/m]) This can be quite limiting - it may be possible to lower the value of Repose to allow a bigger cell resolution although you need to take care that this doesn't cause unrealistic slope failure in the grid (dry or wet areas). The method works by calculating slope from a cell based on 4 seperate planes, each drawn from the cells center (WL point) to the centres of 2 adjoining cells. If the slope of any of these planes exceeds the repose slope then sediment is moved from the cell to the adjoining cells connected by that plane. The volume of material moved is related to how much the slope has been exceeded and the geometry of the cells. In the case of a multi-layer bed the composition of the material transfered is taken from the active layer of the cell. 3. Spatially varying BedUpd --------------------------- This allows the bed to be fixed in specific areas (for example the inflow channel) whilst still allowing sediment transport to take place. This is set by setting the "BedUpd" parameter to a quickin type file rather than a logical value. The quickin file should contain a grid of cell centered values between 0 and 1, where 0 = no bed updating and 1 = full bed updating. Intermediate values may be used to smooth the transition between fixed and updating beds. 4. Grain Roughness trachytope ----------------------------- Implemented trachytope 107 which specified roughness (ks) from sediment composition (with no bedforms). Grain roughness specified in the form ks = a * Db where a and b are input parameters. b can currently only take the form 50, 84 or 90 (i.e. D50, D84, D90) but could easily be extended to other grain size percentiles. Trachytope called in *.tdf file with trachytope number 107 which has 2 input parameters: a and b.