I currently read studies about hydraulic River Geometry. In the context of Erosion Rates in Alluval Channels, the term Control Point was mentioned.
The wording is, "...alluvial channels may erode their beds through time if their downstream control point lowers."
Does it have to do something with the base level?
Base level is the lowest point a river section can flow to, such as lake or ocean level but sometimes mention of base level term is informally used as a term to discuss some major shift downstream in channel that activates channel degradation, as the channel control point(s) has(have) changed. Control points generally refer to a grade control, but also the term is sometimes the term control is used to describe the controlling feature specific to a location at a certain flow value or water level elevation. With time and flow rate, the vertical channel control of degradation may be a root, exposed sill, log, shoal or bedrock, and in locations where discharges during floods must squeeze through a constrained geologic pinch point, lateral controls may contribute to rate and extent of channel degradation.
In response to the quote and my exposure and work in gully systems, it is easy to become very aware of the changes in control as gully nickpoint(s) episodically move headward in response to change, with channels actively extending, degrading, expanding and other areas downstream aggrading or accumulating sediments. But is not unusual to find natural or anthropogenic encouraged circumstances where an aggraded section has accumulated too much or sediment loading is reduced and headcutting and degradation results in deep valley gullies which abandon the recent floodplain.
So there are certain permanent geologic control features and also less permanent to temporary control features that affect and control channel grade and substrate erosion. There may be times that permanent controls are buried by sediments or other times when certain vertical controls of erosion depth are ineffectual when discussing a certain stream flood elevation, as another feature is actually the control.
However, this is my field based understanding, reasoning and have not researched or published relative to the subject. But in informal discussions, when someone discusses baselevel changes due to activities like channel mining or dredging, I know they are not discussing shifts in ocean or lake base level, but the altering of the local in-channel controls that can cause localized changes similar to what one my expect of a base level shift. So there needs to be some leeway as these terms are similar in intent, but not always applied the same way.
But take the Niagara Falls as an example, for contributing streams, that substantive feature is probably more of a base level control than the ocean. So perhaps there will be some further responses that may help more properly define the terms, where they apply and how they should be used. Obviously, local changes in channel controls can produce changes like headcutting and channel expansion that appear similar to base level shifts, even if the ocean base level is perhaps rising. So to some degree, a generic use of the term "base level" may be justified, rather than sticking with just changes in the ocean, as one can find instances where ocean level shift are not responsible for or in sync with shifts far upstream or in headwaters.
A control point is the point where there is a defined relation between discharge (Q) and head (H) like weirs, spillways. . . etc. In simple words we can predict Q by measuring water head(H). You can refer to any book of hydraulics, and I prefer (Treatment Plant Hydraulics by Benefield ). Good luck.
you may refer to " Improving the operation of canal . . . . " which is a useful set of slides ,
I have attached 3 of them.
Thank you very much for your detailed and numerous answers so far!
It's still not really clear to me what exactly a control point is. The authors of the paper wrote about natural and anthropogenic badlands exposed to seasonal climate and tectonics, so i dont think "their" control point refers to mining, dredging or irrigation.
Siad, do you mean the the control point is where the flexion of the riverbed is at maximum? I understood "surface level flexion point" as a point where the river transforms from steep to shallow, (flexion at maximum as i said) ??
Cheers
Control point means relationship between discharge (Q) and water Head(H).If there ise sluice, culvert,barrage etc then by measuring the water head (H) we can find the discharge.
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