Site selection2026-10-03

How to pick a pond site with Web Soil Survey and LiDAR

A pond site works when the land above it sheds enough water to keep it full, the soil under it holds that water, and a short dam across a narrow neck of valley backs up a wide, deep pool. You can screen all three from a desk: the USDA Web Soil Survey gives the soil series, hydrologic group and pond ratings for any parcel, and public LiDAR shows the valley shape well enough to guess the dam height and water surface. A desk screen like that tells you which sites are worth taking to NRCS and which to drop.

What the authoritative sources say

The NRCS handbook Ponds: Planning, Design, Construction (Agriculture Handbook 590) puts the shape of the site first: "A good site generally is one where a dam can be built across a narrow section of a valley, the side slopes are steep, and the slope of the valley floor permits a large area to be flooded." On soil it says "Clays and silty clays are excellent for this purpose; sandy and gravelly clays are usually satisfactory. Generally, soils with at least 20 percent passing the No. 200 sieve, a Plasticity Index of more than 10 percent, and an undisturbed thickness of at least 3 feet do not have excessive seepage when the water depth is less than 10 feet." The Missouri Pond Handbook adds the rule on springs, "As a general rule, avoid pond sites with springs or sinkholes as they may leak," and the field test: "squeeze a handful of fairly moist soil into a firm ball. If the ball does not crumble with a little handling, the soil probably contains enough clay."

On watershed size, Handbook 590 declines to give a single number: "The amount of runoff that can be expected annually from a given watershed depends on so many interrelated factors that no set rule can be given for its determination." Its Figure 11 maps the acres of drainage area needed per acre-foot of storage, with values from 1.5 to 140 across the country, and its worked example is that "a pond located in west-central Kansas with a capacity of 5 acre-feet requires a drainage area of at least 175 acres under normal conditions."

Published watershed guidance, quoted from each source
Source	Guidance
NRCS Handbook 590, Figure 11	Acres of drainage area per acre-foot of storage, mapped by region, 1.5 to 140. "If reliable local runoff information is available, use it in preference to the guide."
Alabama Extension	"A good rule to follow is to have about 15 acres of watershed for every pond surface acre." Pasture on heavy clay "may need only 5 acres" while "a sandy watershed in a wooded area may need 30 acres or more."
Missouri Department of Conservation	"For fish production, about 15 acres of drainage area for each surface acre of water is best." The recommended watershed ratio "ranges between 10-to-1 and 15-to-1."
Penn State	"Normally, a drainage area of 10 to 20 acres yields sufficient water for a one-acre pond in Pennsylvania."

Permit rules are written in the same units. Penn State's Management of Fish Ponds in Pennsylvania notes that in Pennsylvania "A permit is required for the construction of any dam that impounds the runoff from a drainage area that exceeds 100 acres or provides a maximum storage capacity of 50 acre-feet of water," and Missouri warns that "Conversion of streams or wetlands to construct a pond may be against the law." Handbook 590 also says the one thing a map cannot settle: "you should make soil borings at intervals over the area to be covered with water. Three or four borings per acre may be enough if the soils are uniform."

Reading Web Soil Survey for a parcel

Open Web Soil Survey, find the parcel by address and draw an Area of Interest around the pool and the dam line. The Soil Map tab names the soil series; in the Soil Data Explorer tab, under Suitabilities and Limitations for Use, the Water Management category rates "Pond Reservoir Areas" and "Embankments, Dikes, and Levees" as Not limited, Somewhat limited or Very limited. The NRCS Soil Survey Manual says the pond rating rests on "the minimum saturated hydraulic conductivity and the depth to pervious soil material." Under Soil Properties and Qualities, look up the Hydrologic Soil Group, which rates how much rain runs off rather than soaking in. The National Engineering Handbook, Part 630, Chapter 7 defines Group A soils as having "low runoff potential when thoroughly wet," typically "less than 10 percent clay," and Group D as having "high runoff potential when thoroughly wet," typically "greater than 40 percent clay." A watershed on group C or D soil fills a pond from fewer acres, and a basin on those soils tends to hold water. Group A land does neither of those things.

What LiDAR shows before you walk the land

The USGS 3D Elevation Program publishes bare-earth elevation at one-meter resolution from LiDAR over most of the country, in the public domain. A profile across the valley at the proposed dam shows how wide the dam must be at each height, and the contour at your planned water surface traces the shoreline, so you can see whether a 12-foot dam floods a broad bowl or a narrow ditch. Comparing sites that way is the handbook's test, the most storage for the least fill, done on a screen before you walk the ground. LiDAR cannot see soil, springs or bedrock.

What Pond Boss owners do

Moderator Chris Steelman calls Web Soil Survey "a great resource for anybody thinking about building a pond" (2008). The standing caution comes from moderator Theo Gallus, that the maps "show the topsoil, not whether pond-friendly clay is located underneath it" (2007). The map can be wrong in either direction. Member liquidsquid's survey said "nothing but sand and gravel," and the backhoe found heavy clay that held water once compacted (2014). Moderator esshup describes a customer's 1.25 acre site where test holes showed "the only way to ensure the pond would hold water was to put in a liner" (2023). Lunker RAH built two ponds where Fish and Wildlife said the site would not hold water, dug deeper than advised, and they held through two severe droughts (2012).

The regional watershed rules that members quote spread widely. Ambassador Rainman says eastern Indiana "only needs an average of 10-15 acres of watershed per surface acre" (2015), Lunker FishinRod gives "3-5 acres" for Michigan (2021). Lunker Robinson cut a keyway for a dam and found "a spring that went underground upstream" running along bedrock across it (2004). Bob Lusk, editor of Pond Boss, tells owners to "Bring a backhoe out to dig test holes to check soil layers before building a pond" (2012). Ambassador catmandoo says that with NRCS and permits "the biggest issue is impounding a stream" (2016).

Where the tiers differ

Everyone agrees on the method and disagrees on the one number people ask for. The handbook rates watershed per acre-foot of storage and the state guides rate it per surface acre, so the two cannot be compared without an average depth, and a 15 to 1 rule from Alabama or Missouri cannot be carried to Michigan or Kansas. The forum's regional rules are experience with no published basis beyond Figure 11. Every source treats the soil map as a first screen and the test hole as the real answer, and the forum stories show the map wrong in both directions. No source gives a slope or dam height that makes a site good; the published criterion is storage per unit of fill.

What to do

Pull the parcel in Web Soil Survey. Note the series under the pool and the dam, the two pond ratings, and the hydrologic group of the watershed. A Very limited rating or group A soil under the pool is a reason to look at other sites, though it is not a verdict on this one.
Outline the watershed on elevation data and measure its acres against Figure 11 and your state's ratio. If the watershed comes out far over the ratio you will need a bigger spillway and should check the permit thresholds; if it comes out far under, look for another neck of the valley.
Draw the dam line and the planned water contour on LiDAR, and pick the site with the most water for the least fill.
Walk it. Look for seeps, springs, sinkholes and rock outcrops, and ask how neighboring ponds on the same soil hold up in late summer.
Dig test holes across the pool and along the dam line, three or four per acre, and fill some with water. Do not build on sand, gravel, cracked limestone or a spring line without a liner or an engineer's design.
Take the soil map, watershed acres, dam line and volume to the county NRCS office, and ask about stream, wetland and dam permits before hiring a contractor.

Doing the desk work in PondTools

The PondTools planner draws the pond over satellite imagery, as described in planning a pond from satellite imagery, and its LiDAR basin estimate reads the public USGS elevation around the outline, as described in estimating a lake bed from LiDAR. Trace the planned water surface and you get surface acres and an estimated basin. For a storage figure to carry to NRCS, the PondTools volume calculator (also standalone) takes length, width, average depth and a shape factor and returns gallons. Divide the gallons by 325,851 to get acre-feet, which is the unit Figure 11 uses.