Wierd question, but I was wondering ...

Historically, I have always used a large tree that falls in the path of the wetlands line that I "see" while delineating. This has been done so that there is a large reference to look for in the future, and the longevity that a ribbon on a tree provides (vs grass or saplings).

With the proliferation of GPS technology, I am now wondering if I should be focused on "sky view" as I am locating the flag. A large tree that a GPS is held against has to cut down on sky view.

So, what do you do?

*note - I am wary of all the "submeter accuracy" GPS units being freely used in the field and the accuracy of this information in tree canopy vs a parking lot.

If you purchase some really good sub-meter imagery this might work, but most of the free imagery available (NAIP for example) is at best 1m and converting formats degrades it further.

I just use a lot of flagging, 5-10m intervals or closer depending on density with some trees double flagged, and wire flags in grassy areas. Unless there is a fire , controlled burn, or mowing on the grassy areas, the flagging will last around 3-4 years in a good state of visibility. This year I have revisited some wetlands flagged in 2002 and you can still follow the flag line.

Like Tommy, we hang alot of flags. Over the years you could and will lose some, but enough will be still hanging to still find the line.

We've used GPSs for around 6 years now for all of our confirmation maps. I never worry about placement of flag and visibility to the sky. Even in dense forests during the summer we can still usually get a sat lock. Areas that really mess up the signal are in deep gullies. Terrain seems to be the biggest block to sats. You being on the coast should not have any problems I would think. If I do have problems getting a signal I have a laser range finder that takes slope into account. I get to spot where I get a lock and do a bearing distance offset to the flag.

Anyone who says that the processed points are all submeter in most of the conditions we work in would be lying. We strictly use it for generating the initial delineation map for confirmation. Why do you need the whole wetland line survey grade accurate on an entire site? With the map we produce our clients can still use the boundary for planning purposes (avoidance/minimization), and the areas that are unavoidable can then be located with traditional survey methods to accurately calculate impacts. Surveying the whole boundary is a huge waste of client money. I've never had a COE rep question the accuracy of our GPS boundary for confirmation.

The dense vegetation of the coastal plain virtually eliminates all signal at times (depending on vegetation - pocosins are terrible).

It is EASY to get a line on paper that looks good, but have you ever gone up and down a stream and seen the wetland lines cross on paper?!? (a BIG no-no)!!

There are too many times where this initial mapping information makes it onto a final survey and that is what I do not like. I feel that sometimes, this preliminary information makes it all the way into the register of deeds when property boundaries are recorded and that is not good.

Once you generate an "initial delineation map for confirmation". then the client expects that information to be accurate. There is no need to discuss accuracy and methodology with the client - they paid for a line on the ground and on paper and once they see that information, they expect it to be right!

So, back to my original post, now I am concerned with sky view, since often times I DO NOT know who or what equipment is coming behind me to pick up points. I do not prefer to pick up points with our "submeter accuracy" GPS since I cannot project how it will be used in the future.

Unless you are in a completely open area (ex. tidal marsh next to a maintained road right-of-way), you're never going to be able to get the sky view that will give you accuracy you are looking for in a forested situation. Even in the example that I gave, you would probably have several points that do not post-process to submeter accurate.

An opening in a forested area may be a hole in the canopy 30-50' diameter, if your lucky. Now if you happend to bring your rabbits foot, horseshoe, and four leaf clover with you that day and get to that spot at the precise moment when you have 4 or 5 sats. directly overhead you may get a submeter shot. Most of the time you have maybe two sats directly overhead and two or three lower on the horizon(the horizon in this case is your hole in the canopy). The signal still has to travel through the leaves and branches to reach you. Now if you have a GPS unit with multipath rejection you'll probably get a lock, but it will not be submeter even at a 68% confidence level. Bottom line is, an open sky view in a forested setting (in the best of circumstances)will never give you submeter accuracy.

But to answer your question/post since I guess I got off topic...sure be cognizant of sky view. If you can hang your flag on the line in a spot where you have an opening in the canopy then hang your flag there and take your shot, you should get better accuracy. I'm not sure what you would do about the other 99 flags though. As I said before in my original post. A range finder and compass comes in handy for doing offsets.

I disagree with you that there is no need to discuss options with a client. The client expects what you two agree the final product will be. If a client has a choice (speaking from my experience) between two products that both get him to the same result but one is considerably cheaper then I think they should know. However, I do not endorse pawning off a GPS'd boundary as a survey grade accurate boundary to be used to calculate impacts.

From your posts you sound like you don't like anything about using GPS. If I were you I wouldn't use them except maybe to know where you are (+ or - a few feet).

quote:

Originally posted by Brandon Searcey:
Unless you are in a completely open area (ex. tidal marsh next to a maintained road right-of-way), you're never going to be able to get the sky view that will give you accuracy you are looking for in a forested situation.[QUOTE]

That would all depend upon the quality ($$$) of the equipment that is being used. Differential beacons and survey grade antennas on a prism pole help a lot with accuracy. As well, a survey grade, $40,000 GPS unit can have sub-centimeter accuracy, but can still be hindered by sky view at times.


[QUOTE]I do not endorse pawning off a GPS'd boundary as a survey grade accurate boundary to be used to calculate impacts.[QUOTE]
I agree!

[QUOTE]From your posts you sound like you don't like anything about using GPS. If I were you I wouldn't use them except maybe to know where you are (+ or - a few feet).

Nope, never said that, Brandon, I said "I cannot project how it will be used in the future."

Now I am very curious how everybody is handling this issue. After determining in the field where the wetland boundary is, how is this information given to the client and the agencies. I know the design engineers want sub-meter (or sub-centimeter) accuracy for use in CAD, because every inch counts. The projects I'm seeing are down to the foot, for impact area, avoidance, and buffer zones. One of my projects the design firm professionally surveyed in the wetland lines, after I'd flagged them. So my question is what is the industry standard for this right now? Do the delineators flag a line, maybe GPS it,and draw a rough line on a map? Or do you have a survey team come in afterward?

I know the clients want a final perfect line that they can use for impacts and avoidance, as cheap and accurate as possible. Are delineators doing this in two steps, giving a rough line first?

That is how we do it.

Lets say you have a 200 acre property with several drainages and a large creek/floodplain as one of the property boundaries that is slated for a subdivision. We will initially flag and gps the the wetlands over the entire property to generate our confirmation map, but also to be used in the beginning design stages of development (ie. to plan access roads and lot division). It's a given that GPS is not as accurate as survey grade location; however, the differences are not so great that the gps boundary can not be utilized for planning purposes (avoidance/minimization). I've recently been able to compare a site that we GPS'd and that was field surveyed against each other for area and linear footage and the differences were not great. Deviasion in the line was not very remarkable either. I don't remember the exact figures off the top of my head, but if anyone would really like to know I'll post it. When design is complete then the surveyor's (who go back out anyway to start staking out the cl of road, etc) can pick up the wetland flags at the area of impact to give an exact area/linear footage of impacts. We even have our clients locate the wetland boundaries for areas that they may be getting close to in case the line is off too much. This equates to a huge financial savings for our clients (of course depending on the scope of the project). Smaller projects don't see the same savings as larger projects.

How is using GPS'd boundaries any worse than using a hand drawn map, which is an acceptable map for confirmation.

Again it really depends on the project. If you have a Walmart coming in and the whole site is going to destroyed of course you'll have to locate the whole line to survey grade accuracy. However, we would still GPS the line while we are flagging (we work in teams) to produce the initial confirmation map. It speeds up the process instead of having to wait for the surveyor's to give me there line, and plus as I'm delineating I'm attributing the points(ex. A100 PFO) so that when I'm connecting my points I know exactly what area is what. In my experience with getting a wetland boundary from surveyors it's a nightmare trying to figure out where the wetlands vs. where the streams are. Unless the delineator writes on the flag A100 PFO and the survyor is thorough enough to get that information it becomes a mess and possibly more time in the field figuring out exactly what is what.

Like I've said, it gives our clients options. It's worked great for us for 6 years, but who knows, tomorrow some regulator may say that they will not accept a GPS'd boundary for a confirmation map. We all know what one regulator will accept another may not.