A couple of times, I was able to find remnants of stable channel sections on the valley surface. These were the stable bankfull channels which had access to the valley floodplain. Stanley Trimble in his book about piedmont erosion and practices describes the process of gully development, and some of these valleys were filled with sediment, and because the eroded landscape was so unproductive, farmers would intentionally relocate streams to the valley margins to farm the valley. These straightened streams rapidly entrenched in the valley deposits into deep gullies. Sometimes tree roots or bedrock limited the entrenchment. With a combination of historic aerial photos, LiDAR coverage and some field inspections and data collections, in some instances this history of erosion might be pieced together. Another couple of authors I cited in some of my papers on gullies had the last names Schumm and Happ. You may find their information helpful. Working with USFS Soil Scientist Jason Jennings and interacting with Dr. Alan James (USC Geomorphologist) and Dr. David Rosgen were very helpful in understanding some of these processes. Gully energy contained within a narrow channel showed in a few locations of entrenchment beyond the historic valley into the prehistoric surface or basement. Since gullies lack floodplain access, if their margins are well stabilized by forests, their flood energy continues to concentrate on degradation. Quantification might be done on the volume of the original stable channel as compared to the volume of the existing channel dimension.

If dealing with small hillslope gullies, you might check out the coauthored paper on Sediment from a Small Ephemeral Gully in my Researchgate, where the volume of sediment over about a decade was caught and quantified by volume and material density measurements. We, caught and measured/approximated over 50 tons of sediment from 0.25 acres over the decade. If you build a catchment area and find it insufficient in size or that it does not allow enough settling time, you might try adding to it a filter fabric fence described to help filter out the sediment. This would not be suitable for very large gully streams or rivers. Many gullies Contribute to filling of downstream ponds, lakes and reservoirs, and one might try evaluating the infilling information of excess sediment and any dredging activities, change in bathymetry or other elevation changes through time.

As far as capturing and diverting flow in stable drainage lines, one must be careful and consider all stabilization methods. You might check out David Rosgen’s works on stabilization. In some of our gully stabilization or restoration reshaping projects, agricultural terraces less than 1% slope aggraded, causing eventual failure, and terraces with gradients too steep, maybe in the range of 2-4%, they would degrade, and fairly quickly in response to severe rain. Many of the soils that gully have weathering or chemistry issues that contribute to their erosivity. In some instances, about any concentration of water onto sloping terrain will initiate rilling and eventual network expansion into gullying.

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