U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2005–3078

March 2006

Modeling Surface-Water Flow and Sediment Mobility with 

the Multi-Dimensional Surface-Water Modeling System 

(MD_SWMS)

Printed on recycled paper

Surface-Water Model

	FaSTMECH - 2D vertical average and quasi-3D general

steady-state flow.

Applications:

Flood reconstruction.

Habitat analysis.

Instream-flow requirements.

Bridge-pier analysis.

Sediment mobility.

Capabilities:

Import, view, and edit ancillary scatter data sets.

Interactively build data sets for the computational grid,

material properties, and boundary conditions.

Specify model parameters and run the model.

Visualize model results.

Compare model results to measurements.

Requirements:

Topography suitable for multi-dimensional models.

Single thread channel at the upstream boundary.

Measured water-surface elevations for model calibration.

Measured velocity for model verification.

Downstream stage and discharge for flows of interest.

MD_SWMS Version 1

The U.S. Geological Survey’s (USGS) Multi-Dimensional

Surface-Water Modeling System (MD_SWMS) is a pre- and

post-processing application for computational models of surfacewater hydraulics. The system is both a tool and framework that

provides an easy to use interface to a variety of environmental

hydraulic models.

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The tool is a Graphical User Interface (GUI) (McDonald

and others, 2005) that allows the modeler to build and edit

data sets of the modeling system’s computational surfacewater models. The framework links the GUI tool with the

modeling applications. New applications can be adapted to the

framework through modification of the input and output software

routines. In this way, MD_SWMS is flexible and generic, easily

incorporating new models and avoiding the necessity of writing

a new GUI for each modeling application.

The GUI tool is a sophisticated 1, 2, and 3-dimensional

interactive GUI (fig. 1) that is used to build and visualize all

aspects of computational surface-water applications. Surfacewater modeling is a process whereby the modeler builds the grid,

applies boundary conditions, runs the simulation, and evaluates

the results. The MD_SWMS GUI tool facilitates this process by

providing an easy way to apply this process iteratively until a

useful result has been obtained.

The Computational Fluid Dynamics General Notation

System (CGNS) is used to provide the framework for

incorporating surface-water models into MD_SWMS. CGNS

is a database developed to assist the exchange of data between

aerodynamic Computational Fluid Dynamic (CFD) applications

and it consists of two parts: (1) a standard format for recording

the data, and (2) a software interface that reads, writes, and

modifies data in that format (Legensky and others, 2002; http://

www.cgns.org). CGNS provides a bridge between MD_SWMS

and its environmental surface-water applications in the following

ways:

All data designed in the MD_SWMS GUI tool is

written to a CGNS database including descriptions of

the computational grid, boundary conditions, initial

conditions, and application specific parameters.

Modeling applications in MD_SWMS read from the

CGNS database to initialize and run the model after

which the model solution is appended to the database.

The model solution is then read by MD_SWMS for

visualization, analysis, and verification.

The CGNS framework is used to separate the GUI from the

computational models, which allows MD_SWMS to be a single

tool that can be used with many applications.

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The Multi-Dimensional Surface-Water Modeling System (MD_SWMS) is a Graphical User Interface for surface-water flow and 

sediment-transport models. The capabilities of MD_SWMS for developing models include: importing raw topography and other 

ancillary data; building the numerical grid and defining initial and boundary conditions; running simulations; visualizing results; 

and comparing results with measured data.
Multi-Dimensional Surface-Water Modeling

Multi-dimensional models are used where spatially

distributed values of velocity, depth, water-surface elevation, or

bed-shear stress are required. Applications include flood-flow

predictions, flood reconstruction, in-stream flow requirements,

habitat analysis, and sediment transport.

A series of technological advancements have made the use

of multi-dimensional surface-water models more efficient in

terms of time and ultimately cost. These advancements include

modern computing, new channel mapping methods using survey

grade global positioning systems (GPS), and velocity mapping

using acoustic Doppler current profiler (ADCP) linked with

GPS. The majority of effort in using multi-dimensional models

is in the collection of field data, especially bathymetry at suitable

scales; that is, scales corresponding to scales of the desired

results. Field surveys of water-surface elevations and velocity are

used for model calibration and validation. These data are now

efficiently collected using roving or boat-mounted systems.

MD_SWMS Applications

Version 1 contains a single steady-state model of flow,

FaSTMECH, developed at the USGS (Nelson and others, 2003).

Future plans and additions are discussed later in the text. Here

we present a variety of applications that have been modeled

using FaSTMECH within MD_SWMS.

Flow Modeling

Basic output from a hydraulic model such as water-surface

elevation, depth, and velocity magnitude and direction can be

used by engineers in the design and location of bridge piers.

MD_SWMS was used to model the 100-year recurrence interval

flood on the Tanana River in Alaska to aid in the relocation and

realignment of the Alaska Highway Bridge over the Tanana

River, near Tok, Alaska.

Figure 1. The MD_SWMS GUI tool shown with an application of the Kootenai River, Idaho. The GUI features menus, toolbars, treeview of data objects loaded 

into the project, graphics view with tools for zooming and panning, status bar and probe bar for dynamic feedback of data values. The main panel of the application 

shows a portion of a 10-kilometer reach of the Kootenai River with a model prediction of velocity overlain on a georeferenced digital orthoquad. A detail (inset) of 

the solution shows the complicated flow pattern in a sharp bend of the river. Velocity magnitude is shown by color and velocity vectors are shown in black. 
Bridge designs are required to accommodate 100-year

recurrence interval and to withstand the associated streambed

scour around bridge piers. An initial step in the design is

selecting a location that will have low susceptibility to general

scour over a range of hydraulic conditions. If properly designed,

the location, dimensions, and alignment of bridge piers can

reduce the potential for local streambed scour at the piers.

An extensive bathymetric data set and a properly calibrated

hydrodynamic model are needed to design a sound structure.

Detailed topography, water-surface elevations, and velocity

were collected in a 1.5-kilometer reach of the Tanana River that

spanned the existing bridge and a potential downstream location

for the new bridge. The model was first calibrated to a measured

flow discharge of 725 m3/s (cubic meters per second), by

adjusting the roughness or flow resistance in the model so that

the simulated and measured water-surface elevations matched.

The observed spatial pattern of velocity magnitude and direction

with the simulated values were compared (fig. 2).

A model of the 100-year recurrence interval discharge of

1,452 m3/s (fig. 3A) was then calculated by using the calibrated

parameters and a starting water-surface elevation calculated

with a one-dimensional model. Simulated flow angle of

attacks, on the existing bridge piers, which are used to calculate

the susceptibility to bridge pier scour, increased from 38 to

45 degrees on the left bank pier and from 45 to 55 degrees on

the right-bank pier. A second hypothetical simulation (fig. 3B)

of this discharge was run with the existing piers removed from

the channel. Flow directions from this scenario can be used

to determine channel flow angle of attack on piers for the

replacement bridge. Simulated velocity magnitude and direction,

Figure 3. Velocity vectors and contours of velocity for the 

simulation of the 100-year recurrence interval discharge with 

(A) the existing bridge piers and with (B) the existing piers 

removed.

water-surface elevations, and flow angles of attack from these

simulations will aid engineers in the design of a new bridge in

the event that the existing bridge is removed from the channel.

Conaway and Moran (2004) provide a more detailed description

of this project.

Sediment-Mobility Modeling

Sediment mobility can be used to establish the flow

necessary to maintain the geomorphic characteristics of a

channel (Nelson, 1996). The Deer Flats Wildlife Refuge on the

Snake River, Idaho, consists of many islands that provide diverse

riparian habitat for nesting birds. Channel islands usually are

separated from the banks of the river by a relatively swift main

channel and a slower secondary channel. Sedimentation in the

secondary channels can result in attachment of the island to

the bank. Removing sediment from the secondary channels is

necessary to maintain the island and nesting habitat.

Figure 2. Comparison of simulated and measured velocities 

for the 780 m3/s calibration flow. The velocity was measured 

along traverses by using an ADCP; three seperate traverses 

across the river are shown. Measured velocities represent the 

velocity at a point in space and time compared to simulated 

velocities, which represent an average. Therefore, the 

measured velocities are expected to have more variability 

than the simulated velocities.
Figure 4. Model solutions for the Snake River sediment-mobility model. The topography and velocity vectors for three discharges of (a) 200, (b) 425, and 

(c) 700 m3/s show the increasing magnitude and inundation of the island in the center of the channel. In general, the flow rate in the back-bar channel to the 

left of the island is slower than the main channel. The transport strength for each of the three discharges is shown in d-f respectively. At increasing discharge, 

flow rates are sufficient to mobilize coarse sediments in a larger area of the backbar channel. The highest discharge (700 m3/s) is necessary to remove coarse 

sediments and maintain flow in the backbar channel.
To simulate flows needed to maintain the secondary

channels, a two-dimensional model is required that can resolve

the flow routing around an island and the spatial distribution

of bottom shear stress. For preservation of channel islands, the

variations of flow and shear stress with discharge are crucial.

The modeled channel consists of a main channel along the river

right side of the island and a shallow low-velocity secondary

channel. Bottom shear stress and hence sediment transport

capacity of the secondary channel generally is much lower

than the main channel. Figure 4A-C shows the topography and

velocity vectors for three discharges—200, 425, and

700 m3/s. During periods of relatively low discharge, fine

sediment accumulates in this channel. Over time, in the absence

of higher flows, this channel may become completely blocked

with sediment.

To identify the flow that can prevent long-term aggradation

in the secondary channel requires, knowledge of the bed

material within the reach is required. The bed material in this

example reach is composed primarily of coarse gravel that is

rarely mobile, even at relatively high discharge. However, fine

sediments are supplied by tributaries and bank failure, and these

fine sediments are deposited in the interstices of the gravel in

regions of low flow. The principal condition for maintaining

the secondary channel is removal of the fine material. In the

presence of mixed grain sizes, this requires flows that are at a

minimum, capable of moving the coarser material at very low

transport rates.

For the Snake River example, the low-velocity channel

contains gravel approximately 2 centimeters in size. The

initiation of motion for this size is expected to occur at a bottom

shear stress of 10 newtons per meter squared. Using this value, it

is possible to compute the transport rate, defined as the simulated

bottom shear stress normalized by the critical shear stress minus

unity. When the bottom shear stress equals the critical shear

stress, the transport rate is zero and when the bottom shear stress

is twice the critical value the transport rate is one. Results for

the transport strength are shown in figure 4 for the same series

of discharge used to show the flow velocity. For the 200 m3/s

discharge, the coarse material moves in the main channel

only. At 425 m3/s movement is very limited in the secondary

channel, and by 700 m3/ s, coarse material moves throughout

the secondary channel. Thus, by using the computational flow

solution, it is possible to conclude that flows of approximately

700 m3/s are required to produce gravel movement and maintain

the secondary channel free of sediment.

Habitat Modeling

Each spring more than 0.5 million sandhill cranes and a

few endangered whooping cranes use the Central Platte River

Valley, Nebraska, as critical staging habitat during their northern

migration. During their spring visit, most cranes roost in the

central Platte River, standing on submerged sandbars from dusk

until dawn each night. Over the last century, upstream waterresource development has affected the delivery of water and

sediment to the central Platte River, removing high flows and

decreasing the supply of fine sediment. These changes have

resulted in channel incision and vegetation encroachment along

the riparian corridor, both of which tend to stabilize sand bars

and banks; the once wide and shallow channels of the Platte

Figure 5. Output of multi-dimensional hydraulic model showing the 

(a) depth distribution and (b) velocity magnitude along the Rowe Sanctuary 

study reach for a streamflow of 37 m3/ s.

River have narrowed and deepened, and their beds have become

significantly coarser (Kinzel and others, 1999). The changes

in river morphology in part are believed to have altered the

nocturnal roosting habitat used by cranes.

To gain an understanding of how the changing river

morphology affects the roosting habitat, MD_SWMS was used

to simulate crane habitat at the Rowe Sanctuary on the Platte

River. Roosting sites were surveyed by using infrared video, and

the channel morphology and hydraulics (depth and velocity)

were compared to MD_SWMS simulations (fig. 5A, B). The

crane roost maps defined from the infrared video were overlain

on the flow modeling results to identify the ranges in depth and

velocity preferred by roosting cranes (fig. 6). Cranes generally

prefer to roost in water depths less than 0.40 meter with

velocities less than 0.70 meter per second. The habitat value was

then computed by applying the depth and velocity preferences

over a range of simulated streamflows (fig.7).
Figure 6. Histogram showing ranges of depths and velocities used by roosting cranes in the 

Rowe Sanctuary study reach.

Figure 7. Habitat value over a range of stream discharge at the 

Rowe Sanctuary study reach.

Figure 6 indicates that, based on the observed habitat

preferences, the greatest quantity of available roosting habitat

occurs at the Rowe Sanctuary when the streamflow in this

channel is about 37 m3/ s. It is important to realize that these

model results were computed by assuming the riverbed is fixed

and immobile. In actuality at high streamflows, sand could

be deposited on the submerged sandbars and increase their

elevation, which may increase the quantity of available habitat.

Investigating these effects would require modifying the model to

incorporate sediment transport and verifying what influence this

may have on the sandbars. For more information on this project,

see Kinzel and others (2005).

Future Additions

Work on the FaSTMECH model

is ongoing and includes the addition of

time-stepping through variable discharge

using the steady-state approximation

and sediment-transport and channelevolution modules. System for Transport

and River Modeling (STORM), a general

coordinate system two-dimensional

unsteady flow model is currently (2005)

in development (Simões and McDonald,

2004) and is planned to be included in the

MD_SWMS system.

Availability

MD_SWMS is available from the

web at http://wwwbrr.cr.usgs.gov/

projects/SW_Math_mod/OpModels/MD_

SWMS/index.htm

By Richard McDonald, Jonathan Nelson, 

Paul Kinzel, and Jeff Conaway

References Cited

Conaway, J.S., and Moran, E.H., 2004, Development and calibration of

two-dimensional hydrodynamic model of the Tanana River near Tok,

Alaska: U.S. Geological Survey Open-File Report 2004-1225, 22 p.

Kinzel, P.J., Nelson, J.M., Parker, R.S., Bennett, J.P., and Topping,

D.J., 1999, Grain-size evolution of the Platte River, 1931-1998, in

Proceedings of the 10th Platte River Basin Ecosystem Symposium,

February 23-24, 1999, Kearney, Nebraska, p. 9-14.

Kinzel, P.J., Nelson, J.M., and Parker, R.S., 2005, Assessing sandhill

crane roosting habitat along the Platte River, Nebraska: U.S.

Geological Survey Fact Sheet 2005-3029, 2 p.

Legensky, S.M., Edwards, D.E., Bush, R.H., Poirier, D.M.A., Rumsey,

C.L., Cosner, R.R., and Towne, C.E., 2002, CFD General Notation

System (CGNS)—Status and future directions: American Institute of

Aeronautics and Astronautics Paper 2002-0752.

McDonald, R.R., Nelson, J.M., and Bennett, J.P., 2005, Multidimensional surface-water modeling system user’s guide: U.S.

Geological Survey Techniques and Methods, 6-B2, 136 p.

Nelson, J.M., 1996, Predictive techniques for river channel

maintenance: Water, Soil, and Air Pollution, v. 90, p. 321-333.

Nelson, J.M., Bennett, J.P., and Wiele, S.M., 2003, Flow and sedimenttransport modeling—Tools in fluvial geomorphology: England,

Wiley, p. 539-576.

Simões, F.J., and McDonald, R.R., 2004, A modeling system for

2D flow in surface waters, in Advances in Hydro-Science and

Engineering VI, ed. by M.A. Altinakar and others: Proceedings of

the 6th International Conference on Hydroscience and Engineering,

Brisbane, Australia, May 31-June 3, 2004.