# Model help:AgDegNormalGravMixHyd

## AgDegNormalGravMixHyd

This is a module that calculates the evolution of a gravel bed river under an imposed cycled hydrograph.

## Model introduction

This program is a close relative of AgDegNormGravMixPW. It computes aggradation and degradation in gravel-bed river subject to a repeated hydrograph. The sediment is modeled as mixture of different grain sizes and the bedload formulation is that of Parker (1990) that was derived to compute the transport of gravel only.

## Model parameters

Parameter Description Unit
Input directory path to input files
Site prefix Site prefix for Input/Output files
Case prefix Case prefix for Input/Output files
Parameter Description Unit
number of hydrograph entries between 2 and 16 values
number of cycles per year -
bed elevation at downstream end m
initial bed slope -
reach length m
Time step days
Number of intervals
Number of printouts -
Iterations per each printout -
factor by which Ds90 is multiplied for roughness height -
factor by which Ds90 is multiplied for active layer thickness -
Manning-Strickler cofficient r
Submerged specific gravity of sediment
bed porosity, gravel
upwinding coefficient for load spatial derivatives in Exner equation (> 0.5 suggested)
Coefficient for material transferred to substrate as bed aggrades
Parameter Description Unit
Model name name of the model -
Author name name of the model author -

## Uses ports

This will be something that the CSDMS facility will add

## Provides ports

This will be something that the CSDMS facility will add

## Main equations

• time duration of a short flood
 $\displaystyle{ \Delta t_{w} = n_{step,w} \Delta t_{f} }$ (1)
• Total time for flood
 $\displaystyle{ P = \sum\limits_{w=1}^W n_{step,w} }$ (2)

## Notes

This program computes the time evolution of the long profile of a river of constant width carrying a mixture of gravel sizes, the downstream end of which has a prescribed elevation. In particular, the program computes the time evolution of the spatial profiles of bed elevation, total gravel bedload transport rate and grain size distribution of the surface (active) layer of the bed.

The flow is specified in terms of a hydrograph repeated a specified number of times annually, rather than a constant flood discharge and an intermittency.

The river has constant width. The upstream point, at which sediment is fed, is fixed in the horizontal to be at x = 0. The vertical elevation of the upstream point may change freely as the bed aggrades or degrades.In the program it is assumed that all gravel reaching the topset-foreset break is captured in the delta.

The reach has constant length L, so that the downstream point is fixed in the horizontal at x = L. This downstream point has a user-specified initial elevation ηdI.

Gravel bedload transport of mixtures is computed using the Parker (1990) surface-based formulation. Sand and finer material must be excluded from the grain size distributions before implementing this relation.

The grain size distributions of the sediment feed, initial surface material and substrate material must be specified. It is assumed that the grain size distribution of the sediment feed rate does not change in time, the initial grain size distribution of the surface material is the same at every node, the grain size distribution of the substrate is the same at every node and does not vary in the vertical.

The program does not store the vertical and streamwise structure of the new substrate created as the bed aggrades. As a result, is cannot capture the case of aggradation followed by degradation. Again, the constraint is easy to relax, but at the price of increased memory requirements for storing the newly-created substrate.

To perform a numerical calculation with a flow hydrograph, the actual hydrograph must be specified in terms of W constant water discharges Qw, where w = 1 … W, each extending for time duration Δtw. The river is assumed to be morphologically inactive when it is not in flood. The morphodynamic evolution is computed solving the equation of sediment continuity (i.e. Exner equation).

• Note on model running

The program may take a few seconds to calculate, depending on the user’s inputs—this is a calculation intensive program—please give the program some time to make the calculations.

There are no output values at time=0 for the geometric mean diameter of the load and the ration between the total bedload transport rate and the feed rate, because these are calculated in the time loop; they are not initial values.

Due to the many variables that are dependent upon user inputted values in this function the “ReadIn” function is called in the main, instead of in the Initialize portion of the code.

## Examples

An example run with input parameters, BLD files, as well as a figure / movie of the output

Follow the next steps to include images / movies of simulations: