Pond Boss Forums POND CONSTRUCTION Selecting a site How to measure size?

What is the correct way to measure size of pond? Thanks in advance.

Length X Width divided by 43,560 to get acreage. (43,560 square feet in an acre) However it depends somewhat on the shape of your pond and this is a rough estimate.

If you want to be more precise here is an interesting link:

http://www.sfr.cas.psu.edu/water/pond%20area.htm

Buy graph paper; figure out a scale and chart it out. Calculate sq. ft, of each area add them together and, as Cecil says, divide by 43,560.

For simple shapes try one of these:

If your pond is U shaped, this formula should give you ball park estimate of the area. Length ft x width ft x 0.785 = square ft. square ft divided by 43560 = acres.

If you have a round ended long triangle, try this formula: length ft x width ft x 0.523 = square feet. Subtract a little square footage for the rounded corners at the widest base depending on how you mesure it.

If you have an oval pond try this formula: lengthxwidth x 0.785.

If you have a triangle shaped pond: length x width divided by 2.

As a double check, it is best to compare your results with the other suggestions.

To figure the largest it could possibly be consider it a rectangle or square and multiply the longfest length x longest width. All shortages and deviations from this basic rectangle need to be realistically estimated and subtracted from the maximum possible size.

Just had to do this for my permit renewal. The thing missing from this thread is not to waste time trying to measure a complex pond shape, there is an easier way.

If your pond is a simple shape use Bill's formulas. If it is irregular like mine, the easiest and most accurate way is to obtain an aerial photograph from the county tax assessor's office. The photo quality will vary based on the technical capabilities of the county. My county is flown every five years and I was lucky to get a 6-month old 24" x 36" photograph with a scale of 1" = 100' for $25.

First look at the link that Cecil provided. Now take a ruler and draw a series of rectangles that best match the outline of your pond. The rectangles do not have to be uniform. Use all different sizes. Cover as much of the open water with one big square or rectangle then fill in the rest. They do not have to fit the shoreline perfectly, just try to balance the amount of land within the rectangles to the amount of water not in the rectangles (you'll see what I mean when you get started). I drew mine with permanent markers on a transparency overlay in order to preserve the photo. My pond has a very irregular shoreline so I had to draw approximately 10-12 rectangles. Number the rectangles and calculate the area of each by multiplying the length times width (convert to feet). Add up all the rectangles to get the total square footage of the pond. Divide by 43,560 to convert to acres. It's also nice to have the aerial photograph on hand.

Do any of you use Terra server?? I measure alot of ponds and lakes this way, it is Very Very acurate!!! All you do is just click around the outer area of what you want to measure and it will give the acreage...I have measured tracts of land before and it is DEAD ON with the survay.

Also has any of you used the GPS's that measure acreage? I have they are good as well!

big_pond, I have used Terra Server before but I can't figure out how to do what you suggested. I can easily get an aerial of my pond but when I try to click around the image nothing happens.

Big Pond,

Good point, Terra Server is a great source. For smaller ponds, you may need to purchase the high resolution image. A GPS could be used to walk the shoreline and calculate the area. There is other mapping software like Terrain Navigator that can be used provided the pond is large enough to be mapped, or you can always sketch it in using the software. I have provided a link to the USFS wetland mapper, which is fairly new. Many of your ponds may be included on this database if your particular area is covered. Follow the sequence through to the mapper and then zero in on your area.

We use Terra Server images at work quite often and I have a couple framed in my basement of my favorite hunting and fishing spots. Personally, I still favor the county photo approach but its a matter of availability and preference.

USFS Wetland Mapper

Just curious...

Could you use a range finder and point it at various stakes around the pond and go from there on paper?

Never used one of the range finders so I don't know how accurate they are.

Cecil:

Sure as a simple survey method that's a good idea. My experience with range finders is limited to the target range, golf course and field trials but I'm sure it would work well for simple pond shapes and would be faster than a measuring tape. Complex shapes like my pond would be a problem because you would need multiple targets around all of the bays and points, which would be a logistical nightmare not worth the effort.

You could do what Bill mentioned and use the rangefinder to shoot a rectangle (or even a radius) that contains your pond and use that as a maximium value and then adjust downward.

Of course there is error associated with all these methods except differentially corrected survey grade GPS or traditional survey methods, which are I think are beyond the investment we're talking about here.

Once I received my aerial photograph it took me about an hour to calculate the area of four ponds. I had to do it because the regulator who was reviewing my permit renewal accused me of having 12-acres of water, when I was only permitted for 5. Turned out to be three just like we had told him on the application. Three down, two to go.

Rob A,
You have to have a subscription to use these advanced features of measure land and water....but beleive me it is WELL worth it..

Steve:

You say you need a permit renewal? Could you explain what type of permit and who would be regulating it?

Thank you,
Dan

Dan:

My project invloves wetlands so a permit from the MDEQ (State) is required under Part 303. My area of ground disturbance exceeds one acre so a Soil Erosion and Sedimentation Control Permit is required from the County. My township also requires a Class B Earth Change permit.

Other permits may be required by the State, for instance, if the created water body exceeds 5-acres or is within 500-feet of a lake or stream (Part 301) or the disturbance is located within a floodplain (Part 31). There are too many less common permit types to list but they may include dams, critical dunes, designated environmental areas, and much more. Here is a link to the State's website for more information.

State of Michigan Permit Information

Steve,

Thank you for the information. I saved it for future reference when questions arise.

I was fortunate to purchase my place with a new (2 years old) 6 plus acre pond on it. I can't imagine going thru the Twp, County, State and Federal regulations, permits and other "stuff".

Thanks again.

Dan

Years ago, I forced my teenage daughter to go with me with a 100 ft tape measure to accurately measure my 2.5 ac. pond. She still complains about it (6 years later), it is her only "I had a hard life." story. It was well worth it, listening to the complaining was and still is priceless. I recommend this method for any pond less than 6 acres....

Great post Dennis.

Nick Jones
www.soilmovers.com

I had a friend who works in the engineering department of a utiity company set up a transit. He shot angles about every 15' around the perimeter of the pond and entered same into a CAD program, which drew an image of the pond and calculated area. Drawing same on graph paper is usually the most viable option for the average Joe, and although not totally accurate, it is pretty fair estimation, which for most uses, if close enough.

Lots of the counties are getting GIS systems. At least some of these that I have seen allow you to easily calculate the size of any property.

Also, I believe the ASCS/NCRS services now have some software that will calculate acreages for you.

Either way could be a lot faster than measuring / calculating it by hand. Maybe not as satisfying , but pretty quick.

That is my method. Average out the inconsistencies
inside and outside your drawn rectangles, triangles, and circles.

I use ArcGIS to do my acreage measurements. I grew up in Minnesota where it is very simple to find the acreage on flat and relatively square fields, I moved to Virginia and I was completely lost in my own internal acreage guesses. This site has been fixed that. It is very simple to use and accurate. When I first found it I tested it against known square footage measurements and GPS calculated measurements and it was always close enough that I kept using it.

http://www.arcgis.com/home/webmap/viewer.html?useExisting=1

Try http://acme.com/planimeter/

I dont know how accurate it is but the NCRS Web Soil Survey will give you a size.

Esshup also posted a page that I have used in the past also but have not found it to be as accurate. One thing I should have mentioned is that the overlay map can make a big difference. ArcGIS uses maps from Bing (Microsoft) where Planimeter uses maps from Google. For my property, the Bing maps are only about 5 months old with the Google maps are about 3 years old and with a much lower resolution.

This difference may skew my measurements but I tend to find that Planimeter says everything is about 10-15% larger then my other measurements.

I recommend that you use every kind of measurement available and then average out the results!

Joe

I used what Cecil suggested in the first post. Google Earth has a ruler feature that gave me my length and width numbers, then I just used that formula. My lake is triangular shaped,sort of, and the surface acreage came out very close to my original estimates.

Here's a link that may explain it better.


Ohio State Calculator

http://www.freemaptools.com/area-calculator.htm

I use the link above after swithing from map to satellite