Okay, so this week's Seafloor Sunday isn't really the sea, but it is some great bathymetry data so I'm going to show it anyway. The bottoms of rivers are dynamic environments. Depending on the river, the season, and myriad other factors the bed of a river can change drastically from week to week or month to month. In many cases, most of the work of transporting and then redepositing large volumes of sediment -- that is, reshaping the landscape -- is done during flood events.
The image above, of the Hudson River in New York state, nicely shows sandy bedforms that have developed on the river bed. Sedimentary particles in the sand-sized range can be carried in suspension during floods for short distances, but most of it, especially the coarser stuff, will bounce along the bottom. Self-organizing bedforms are the result of this interaction of fluid and particle movement.
Here's a blurb about the mapping project from the NOAA site where I found the image:
In 1998 the reserve, working in partnership with Hudson River Estuary Program and several academic institutions, began mapping the submerged lands of the Hudson River Estuary. This is being accomplished using a suite of geophysical tools including multibeam swath sonar, sidescan sonar and subbottom profiling using CHIRP sonar and ground-penetrating radar. The geophysical data have been supplemented with sediment profile imagery and sediment sampling including cores and grabs in an attempt to link geophysical properties with biological function. Products developed from these data include acoustic images and interpretive digital maps (See image above right). The latter include maps of anthropogenic features, recently deposited fine-grained sediments, sediment grain size, bedforms, depositional and erosional areas in the estuary and river bottom morphology. The ultimate goal of this program is to better understand how the bottom of the river provides habitat for the living organisms found there.
Image: Hudson River bedforms / NOAA
