It is interesting that many features of some large geologic systems, such as a river (a fluvial system), can be replicated on a small scale in the laboratory. Using a stream table in the department of Geography and Geology at the University of Nebraska we have been able to produce the equivalent of meander bends, mass wasting of cut banks, flood plain development, terraces, alluvial fan/delta progradation, headward retreat and sorting among other features and processes. The purpose of this web site is to illustrate some basic aspects of fluvial system behavior using our stream table. This is a downstream view of the stream table used to take the photographs in this web site. It measures 13 feet long and 3.5 feet wide. A flow meter allows controlled discharge. Six ports exist (associated with the red hoses) from which water can exit into the table. In this simulation we only used one port at a low flow rate of .3 gallons per minute (gpm), since we have found that relatively low flow amounts over a period of days produces the most interesting and varied set of features. The medium through which the water flows through and over is Platte River sand. In the adjacent photo can see a channel as it appears after a day and a half of flowage. The original geometry of the sand was as a body that extended half the stream table, with an upper surface sloping slightly downstream, and a leading edge dipping about 20ˇ. By the end of the experimental run the sand will be redeposited so that it extends the length of the table, forming a broad sand apron with a lobate front. This depositional feature could be considered an alluvial fan and/or delta complex.
This is an oblique view of the channel and depositional fan that developed after about two hours of flow. Note the 6 inch protractor and fish for scale. The channel is quite sinuous, and the migration of the inner bend with time is evident in the marked channel scars. Down cutting through the steeper front of the sand bodies occurs fairly quickly initially. Steep cut banks are also evident. Deposition in the fan is the form of thin lobes that prograde out into the inch or so of standing water, one of which is noted on the photo. In the very upper left corner standing water which feeds the flow occurs.
This is a map view of an upstream portion of the same channel as above. Again the evidence of the sideways migration of the meander is evident in the old channel scars. The scar of an old channel that used to feed the main channel when it was at a higher level is evident. This elucidates one difference between real world drainage networks and the ones of this stream table. At the upper reach of the channel system a branching geometry usually exists. As the channels lengthen, cutting back into the sand body (a process known as headward retreat), in the stream table it is common that one of the channels is abandoned, as the other captures more water, cuts down and lengthens. This is not characteristic of real-world fluvial systems. What is the difference? For this stream table, the water actually leaks out of the saturated sand at the headwaters. It roughly the equivalent of a groundwater fed system. In real life rainfall would likely continue to feed the channel and it would not be left hanging.
This is an oblique view looking along the length of the stream table after a day. The depositional fan has grown and now spans the width of the table. Compare its extent with the photo above. A branching pattern of channels is seen on the fan, and this mimics real life patterns. Further upstream a steep cut bank can be seen. Small scale mass wasting occurs here. The channel has shifted to the right since cutting this bank. In its migration back and forth it has now formed a flood plain of a sorts. The head of the channel has migrated to a foot and a half from the source.
Significance for environmental geology? The above gives you some idea of the fluvial system features and processes that can be replicated in the stream table. They reinforce the idea that fluvial systems are dynamic, and that channels migrate and switch with time, and that other processes such as mass wasting can be associated with this behavior. When living next to a river this needs to be remembered. A river bluff may provide a gorgeous view for a home, but it also may be a vantage point that physically retreats with time. The Mississippi may go past New Orleans now, but historically it doesnŐt like to stay put, and may switch to another part of this huge depositional fan. Would you like to see more images and discussions of stream table fan/deltas or of channel migration?
If you have any questions or comments about this web page please contact Harmon D. Maher Jr. at University of Nebraska at Omaha (email@example.com). Thank you!