> The Pecos River is not usually much more than a damp ditch, it does meet the statutory definition of navigable in the State of Texas. We have to determine the area of the river bed that is public lands but with all the rain we’ve had lately, it’s been a tough job. Plus all the salt cedars, the steep banks. Heck, it’s a real pain to meander the river.
>
> Apparently someone in the GLO Minerals office came up with a new method for determining area of the river bed. They are running a polyline down the middle of the river on their GIS software and then offsetting the line 15 feet on either side (30 feet being the minimum width of statutory navigability). Trim the polygon by projecting the GIS section lines and we are done! No need to get a crew out, no waiting for flood conditions to end. All from the comfort of the GIS at your office with our increasingly infamous “Original Texas Land Surveys” shapefile.
>
> Thank god the staff at the GLO Minerals office are looking out for the public interests.
Actually, I’d think a very rational approach to that problem would be to measure between the gradient boundaries at intervals and take an average for a particular reach of the Pecos. Applying that width to either side of centerline of the channel as may be digitized from an aerial photo is a good, practical solution in my view.
That method:
(a) preserves the State’s interest in the bed in that it represents an area that is is based upon actual measured widths and so is good estimate and
(b) doesn’t waste time on delineating a boundary that no two surveyorss will be able to duplicate and that over time will shift position even if they did.
An upland owner of a survey that was patented on field notes crossing the Pecos River can still argue that the bed was relinquished to them. If only a part of the bed was relinquished, the above method is an extremely practical way to partition the bed between the State and upland owner.
A very similar problem would be encountered trying to surveying along the Rio Grande above Presidio, where the actual river is completely overgrown in salt cedar so thick a dog couldn’t crawl through it and the river itself is an floatable trickle of a creek full of snags other than from those rare times when it floods. There, the centerline of the river can be located fairly readily, either from aerial imagery or by GPS from a boat when the river is up during one of the few times when it can be navigated.
The banks? The channel is regular enough that it really doesn’t matter for area computation where it is as long as the average distance from the centerline is a good value.