River Geomorphology Videos:
These videos were made to help students better understand geomorphic processes in rivers with special attention to the effects of channelization and gravel mining. The clips are intended for use by an instructor.
The clips were produced by Little River Research and Design (LRRD) under contract with the Missouri Department of Conservation. The US Environmental Protection Agency Region VII, through the Missouri Department of Natural Resources, provided partial funding for this project under Section 319 of the Clean Water Act. Many were made using the Emriver movable bed model
These videos may be freely used and copied as long as they remain unchanged, with all logos and other graphics intact, and with acknowledgment of their creators and funding agencies.
About the Creators
These videos and several more are available on a DVD from Little River Research and Design. The DVD contains a total of 59 videos and the Teaching Guide and can be obtained from the LRRD website. For more information about these clips, contact the Missouri Department of Conservation Streams Unit, or email LRRD at firstname.lastname@example.org.
Kimi Artita and Jesse Riechman assisted with this production, and Mike Covell of Southern Illinois University - Carbondale provided technical advice. All videography, post production work, and video descriptions were done by Steve Gough. Emriver and the green meandering river logo are registered trademarks of Little River Research and Design.
Please cite videos from this collection as: Gough, S. 2007. River geomorphology videos. DVD. Little River Research & Design, Carbondale, IL; www.emriver.com.
Map & Aerial Clips
(1:05 m Flash Video 3MB, Dec11 09)
A sequence of eight aerial photos running from 1939 to 1996 show the remeandering of a reach that appears as a straight, probably recently channelized reach in 1939. The location is six miles north of Grant City, Missouri. An animated blue line traces the channel changes.
Note the vegetated bars left behind as meander loops grow. You can also note the severely incised tributaries. Note also the extreme channel shifts from 1983 to 1996, especially in the northern end of the frame.
Note also that there appears to have been rechannelization of some reaches, and I suspect bank armoring, especially where the farm structures are threatened, just west of "1951" in the photo.
Emriver River Model Clips
(2:35 m Flash Video, 8.6MB Dec21 09)
This is a time-lapsed Emriver channelization demonstration in which a meander loop is cut off. In this case the channel length between two points is more than halved, so slope would increase by a factor of 2+. The playback speed varies and is noted on the video.
Note the relative stability of the system before channelization, in which a small amount of sediment is moving through the reach, but there is little bank erosion and by one definition - sediment in = sediment out - the system is very stable. A moving circle and the words “uniform bedload transport” illustrate this.
After the channelization note bank failures both up and downstream, and that the channel slowly reestablishes a meandering form so that its overall length is about the same as before the channelization. Graphics show how bedload transport greatly increases due to incision and bank erosion upstream of and within the reach.
During the remeandering process, note that there is a net export of sediment—you can see this by visually comparing sediment movement into the reach versus that out of it.
Near the end of the clip (2:17), transect graphics appear. These show the wide, unstable nature of the channelized reach versus the narrow, more stable upstream reach.
(0:35 m Flash Video, 2MB Dec 21, 09)
Sediment is removed from the lower end of a straight reach causing one or more headcuts to travel upstream. The first headcut is emphasized with an arrow that fades as the headcut becomes indistinct. As the incision progresses the channel begins to meander and form bars/terraces and the channel evolves. Use the pause control in this short clip to take your time looking at these forms.
Good short illustration of headcutting, incision, and subsequent channel evolution.
(0:58 m Flash Video, 3.2MB Dec 21, 09)
This clip shows how headcutting and incision in a main channel influences a smaller tributary. Sediment is removed from the larger channel (here using an aspirator, out of the frame to the right) causing it to incise. The headcutting and incision affect both the main channel and the smaller tributary. Dye pulses show velocity and relative depth. Note how incision is indicated by the formation of terraces in both channels.
This has many applications to real world problems. This demonstration shows how tributaries are influenced by vertical instability such as that caused by channelization. We can compare this with the large gullies and tributary incision seen in the aerial photos of the channelized Grand River (see the first video on this page).
(0:43 m Flash Video, 2.3MB Dec21 09)
A straight channel is formed in the Emriver model. Speed is x10. After flow begins, the channel slowly forms regular meanders and point bars. Note how the meanders tend to migrate in a downstream direction. The meander bends also expand the meander belt width until about 0:34, when they cease to move outward and migrate only in a downstream direction. Geomorphologists would argue that the channel reaches a point of stability then as sediment inputs to the reach match outputs and the reach no longer has net erosion. You can see this by observing sediment movement into versus out of the reach.
(0:28 m Flash Video, 1.6MB Dec 21, 09)
Here the view is upstream. A clearly-defined headcut moves up through the channel, the water table is lowered as the channel incises, and the floodplain wetland becomes dry. Note formation of small terraces on both sides of the channel as it incises.
(0:43 m Flash Video, 2.4MB Dec 21, 09)
This clip shows a vertical view of a small wetland being drained as the channel near it incises and the water table elevation drops. Note the formation of a sequence of terraces as the channel incises. Here incision was caused by removal of sediment downstream using an aspirator.
(0:42 m Flash Video, 2.3MB Dec 21, 09)
This clip shows a closeup of bank failure in an incising channel. Here the media in the Emriver has been compacted so that it is more cohesive. This cohesion allows for significant undercutting before classic cantilever failure occurs. Note how the failed material is gradually removed by flow, and how series of point bars/terraces form opposite the failing banks as the channel incises.
(1:28 m Flash Video, 4.9MB Dec 21, 09)
The clip opens with a self-formed channel best described as braided. Flow is stopped and the channel is "reamed" by forming a central straight channel with banks made of the bed materials. When flow resumes the channel immediately remeanders and eventually removes most of the bed materials pushed against the banks.
(1:39 m Flash Video, 5.3MB Dec 21, 09)
Early in the clip the channel thalweg is mined, producing a strong headcut (denoted by an arrow) that migrates upstream. As sediment continuity is disrupted we see incision downstream of the pit as well. As the clip progresses, not the formation of terraces on the point bar at bottom left. At 0:47 a pit is excavated in the large terrace/bar at the center of the frame. As the channel captures this pit, we again see a headcut migrate upstream and further incision. As the channel adjusts, note that the surfaces at the bottom center of the frame, which were formerly at bed level, become terraces as the main channel incises. At the end of the clip the channel is forming a new equilibrium form within terraces on each side.
(1:19 m Flash Video, 4.4MB Dec 21, 09)
As the clip opens you see shallow flow with uniform bedmaterial transport throughout. A small low head wier or dam is installed. This produces deep subcritical flow above the dam and critical flow over it. Below the dam we see supercritical flow.
The deeper, low velocity flow above the dam cannot move the coarse bedload (Q = VA, and since A is greatly increased and Q is unchanged above the dam, V is greatly decreased) and we see deposition occur until depth is shallow enough (and A small enough) that the increase in V moved bedload again. Deposition occurs to the top of the dam.
When the dam is installed, we see a classic disruption in sediment transport continuity. Coarse transport essentially ceases through the dam until deposition builds a higher streambed. Sediment is blown out below the dam (often scoured to bedrock in the real world) This is the well known "hungry water" effect seen below dams.
At low-water crossings in the Missouri Ozarks, many of which are essentially low dams, we often see this condition, manifested as a wide, sediment-filled channel with low banks upstream of the bridge. This contrasts with a deep, scoured channel below, sometimes with high, unstable banks.
At the end of the demonstration, the downstream gate is lowered and a hydraulic jump appears which is then drowned as stage increases. The depositional dune and slipface then move past the dam. The gate is then raised somewhat, allowing a jump to reform and sediment is blown out below the dam.
(0:40 m Flash Video, 2.8MB Dec 21, 09)
This clip shows basic hydraulics over a weir with a small amount of plastic media in the flume. At the clip beginning dye is injected into flow upstream of the weir to show the transition from relatively deep, low velocity subcritical flow to critical and supercritical flow over the weir.
Downstream of the weir, supercritical flow is much faster and shallower. As the downstream gate is closed, stage rises and a submerged hydraulic jump appears downstream. Here we can also see the loss of energy due to the jump by comparing the elevation of the water surface below the weir with that above the weir. This energy loss is one of the things that make grade control structures work - they act to dissipate the energy of flow at a point of our choosing.
Note the turbulence and reverse roller (the sort that is very dangerous to be caught in) below the weir.