How to Map Field Drainage Problems for Free (Find Where Water Stands)

Field Forge 3D · Field guide

Every farm has that spot: the corner that's still greasy when the rest of the field is fit, the low patch that drowns out in a wet spring, the headland the sprayer sinks into. Standing water costs twice — once in the drowned-out yield, and again in the compaction from working ground that wasn't ready. Before you spend anything on tile or dirt work, it pays to actually map where water goes. Here's how to do that for free.

Wet spots are a terrain problem first

Soil type, compaction layers, and broken tile all play a part — but water obeys elevation before it obeys anything else. A few inches of fall decide whether a rain moves off a field or sits on it. That's why the same low spots drown out year after year: the shape of the ground doesn't change, only the rainfall does.

It also means you can find most problem spots from terrain alone, before you dig a single test hole. The goal of a drainage map isn't engineering precision — it's knowing where to look, what's connected to what, and roughly how big each problem is, so the conversation with a tile contractor (or your own backhoe) starts from evidence instead of memory.

Free ways to find where water stands

1. Walk it after a rain — and record it properly

Nothing beats ground truth. The day after a decent rain, walk or drive the field edges and note every place water is standing or the ground stays saturated. The mistake most operations make isn't skipping the walk — it's keeping the results in their head. "The wet corner by the gate" is not a record. Mark the spot on a map you keep, with a date, so this year's observation can sit next to next year's.

2. Read the history in aerial imagery

Past imagery is a free drainage survey you already paid for with time. Drowned-out patches show up as dark, bare, or thin spots in summer imagery, and ponding shows directly in shots taken after wet spells. Google Earth's historical imagery slider is the easiest way to flip through years; some county GIS viewers add more recent flights. If the same stain shows up in three different seasons, that's not weather — that's your ground.

3. Check public elevation data

Much of the U.S. now has LiDAR-derived elevation available through public programs, and many county GIS viewers can show contours or hillshade built from it. Tight contour circles and flat, closed depressions are your candidates. The catch: reading raw contours takes practice, the viewers are 2D, and none of them know where your field boundaries are — you're eyeballing your fields onto someone else's map.

4. Use your yield history

If you keep any per-field or per-area yield records, the wet spots are already in them: the areas that always come in light in wet years but fine in dry ones are drainage-limited, not fertility-limited. Even coarse per-field records help separate "this field has a water problem" from "this field has a soil problem."

What a useful drainage map needs

1. Your boundaries on real terrain. The low spots only mean something relative to your field lines, not a county parcel map.
2. The connections, not just the spots. Water that stands in one place got there from somewhere. Knowing the flow path tells you whether one outlet drains three problems or none.
3. A rough size on each problem. "Half an acre that ponds" and "six acres that pond" are different conversations with different price tags.
4. A record you can keep and compare. Drainage work is judged season over season — the map has to persist, not live in a screenshot.
5. A format you can hand to someone. A tile contractor, an agronomist, a landlord — the map is worth more when it exports to something they can open.

Terrain tools that do the looking for you

Field Forge 3D's Ranch Mapper is a free web app that puts your drawn field boundaries on real aerial imagery over real 3D terrain built from public elevation data — and it includes a set of beta terrain-analysis tools aimed at exactly this job:

• Ponding & watershed (beta) — finds the closed depressions in a field's terrain where water would collect, estimates roughly how much they'd hold, and traces the drainage network that feeds them.
• Drainage trace (beta) — follows the steepest downhill path from where water lands and sketches a suggested line to give it a way out — a starting sketch for the tile conversation, not a design.
• Irrigation zones (beta) — splits a field into zones that tend to shed water versus collect it, drawn as an overlay on the terrain so the wet-tending ground is obvious at a glance.

An honest caveat, stated in the app too: these are relative, terrain-only models. They compute from the shape of the ground — they don't know your soil type, your rainfall, or the tile that's already buried. They're built to tell you where to look first, and they're labelled beta because that's what they are. Verify on the ground before you spend money; none of it is an engineering determination.

The rest of the record-keeping lives in the same place: each field is saved with its acreage (the standard map acre, measured from the boundary you draw), notes and markers for your after-rain observations, and CSV/GeoJSON export so nothing is trapped. It's free while in beta — nothing locked today, and no sign-up is needed to start.

The order of operations

Map first, dig second. Walk the field after a rain and mark what you see; flip through the imagery history to confirm which spots repeat; run the terrain tools to see how the spots connect and what feeds them; then take that map — not a memory — to whoever is pricing the fix. The free version of this takes an afternoon. Guessing wrong on tile placement costs a lot more.