---
title: "flood your field on purpose: how a wet-year flood becomes next year's water"
canonical_url: https://ensurance.app/guide/flood-your-field-on-purpose
markdown_url: https://ensurance.app/guide/flood-your-field-on-purpose.md
subtitle: flood-mar and ag-mar explained — on-farm recharge that banks surplus underground instead of watching it leave
category: how-to
---

# flood your field on purpose: how a wet-year flood becomes next year's water

*flood-mar and ag-mar explained — on-farm recharge that banks surplus underground instead of watching it leave*

When the wet year finally shows up, most farms watch surplus water leave. Flood channels fill, snowmelt races past, stormwater dumps to a ditch — and the aquifer under the same field keeps falling. **Flood-MAR** (flood managed aquifer recharge), also called **agricultural managed aquifer recharge** or **Ag-MAR** / **on-farm recharge**, is the practice of flooding compatible cropland, recharge basins, and reconnected floodplains *on purpose* in the off-season so that water sinks in and banks underground for the drought year.

That is the honest how-to answer for a farmer or district asking what to do with wet years: stop treating every flood as only a liability. Some of it can become next year's supply.

If the well is already failing, read [why your well is running dry](/guide/why-your-well-is-running-dry) first. For the full recharge map, start at [managed aquifer recharge](/guide/managed-aquifer-recharge). This post is the commercial flagship — what to build on working land, what it costs relative to a new reservoir, and who funds it.

:::johnson
**flood the field on purpose in the wet year** — bank the surplus underground where it does not evaporate like a surface lake.

[talk through a recharge site →](/contact?from=guide&topic=aquifer-recharge)
:::

## what flood-mar and ag-mar actually are

**Ag-MAR** deliberately routes wet-year, storm, and snowmelt water onto working farmland so surplus surface water percolates into a depleted aquifer for later recovery. Compatible crops are typically dormant-season or flood-tolerant systems — alfalfa, pasture, some vineyards and orchards where growers and agronomists have tested inundation windows, plus dedicated recharge basins and fallow ground with the right soils.

**Flood-MAR** is the broader landscape version: capture flood peaks on working landscapes, flood bypasses, and reconnected floodplains — not only on a single field. California's Department of Water Resources Flood-MAR program is the best-known public flagship for this approach.

Both sit inside the larger [managed aquifer recharge](/guide/managed-aquifer-recharge) family. The difference from a classic spreading basin alone is that production land stays in the portfolio: you are using the farm as infiltration infrastructure without permanently taking it out of use.

## how on-farm recharge works (honest mechanics)

1. **Find surplus water with a legal path.** Wet-year river water, storm flows, or snowmelt pulses — plus the diversion rights, contracts, or district rules that let you move them onto land.
2. **Match soils and crops.** Coarse-to-medium soils that infiltrate; crop systems that tolerate standing water for defined windows; avoid fields where prolonged flooding damages roots, food-safety constraints, or contaminant pathways.
3. **Spread and hold.** Contours, berms, gates, and temporary inundation turn a pulse into soak time. Dedicated **recharge basins** sit alongside fields when you need controlled infiltration without crop risk.
4. **Measure the bank.** Monitoring wells, soil moisture, diversion meters — so "we flooded" becomes "acre-feet recharged" and, where your basin has banking rules, a credited deposit.
5. **Recover in the dry year.** Pumping under the same basin rules, trades, or district allocations — subject to local water law, not wishful thinking.

Modeled **Ag-MAR / field recharge can reverse water-table declines of up to ~2.5 m/yr** in reviewed scenarios (Kebede et al., 2024). That is a modeled upper bound, not a guarantee for every field. Site hydrogeology and competing pumping decide what you actually get.

Flood-MAR also doubles as **flood-risk reduction**: peaks that used to smash downstream infrastructure can be attenuated on designed landscapes. Habitat and soil-health co-benefits show up when inundation is managed rather than accidental.

## why this beats "build another reservoir"

Surface storage is the mental default. It is also slow, capital-heavy, and evaporative. Flood-MAR is **often more cost-effective than new surface storage** and stacks flood-risk reduction with ecosystem co-benefits (He et al., *Science Advances*, 2021). The reservoir under the farm is already built; you are paying to fill it, not to pour a new dam wall.

| Approach | What you buy | Typical friction |
|---|---|---|
| New surface reservoir | Evaporative storage + long lead time | Cost, permitting, land take |
| Deeper wells | Temporary access to a falling table | Infinite chase; can worsen subsidence |
| Flood-MAR / Ag-MAR | Underground bank + flood peak shaving | Soils, water quality, ops discipline, clear credits |

Limits to say out loud: some water evaporates before it infiltrates; clogged soils need rest and maintenance; water-quality rules (nitrates, pesticides, pathogens) can block sites; and without [groundwater banking](/guide/groundwater-banking) accounting, "I recharged" may not mean "I can withdraw later."

## the bankable stack — not a favor to the basin

On-farm recharge is too often framed as a public favor the grower does for everyone else. Flip that. The water you sink is water you — or a contracted partner — can draw later where the rules allow. The returns stack:

- **Recharge volume** banked for drought
- **Flood safety** for the farm and downstream neighbors
- **Habitat and soil** co-benefits on inundation-compatible ground
- **Subsidence risk reduction** where overdraft has been compacting the aquifer

That stack is why cities, GSAs, food and beverage companies, and capital providers have a self-interested reason to help fund the gates, berms, basins, and monitoring — not as charity, as shared infrastructure.

## who pays, and how ensurance fits

The people who depend on the aquifer — farms, irrigation and water districts, cities, food & beverage, investors — fund the recharge upfront and hold the banked water as an investment position, not a grant that expires.

[ensurance](https://ensurance.app/?from=guide) prices that stack (via natural-capital accounting / RealValue) and routes proceeds to the agents and stewards operating the recharge. A [certificate](/specific?from=guide) can attach funding to a **named recharge site or basin**; [coins](/general?from=guide) support broader water funding. Either way, what you hold is a **funding position** — not land title, and not a water right. The water entitlement remains whatever your state and district law already say.

[`aquifer-recharge.syndicate`](/aquifer-recharge.syndicate?from=guide) is one place that shared basin dependency can coordinate. For the accounting layer on top of the field work, read [how groundwater banking works](/guide/groundwater-banking).

## what to do next

### if you farm or manage land

Inventory soils, dormant-season windows, and whether your district already moves wet-year water. Talk to your irrigation district or GSA before you berm a field alone — the water path and the credit path both matter. [Explore specific ensurance for a named parcel or recharge area →](/specific?from=guide)

### if you run a district, city, or utility

Flood-MAR is cheaper resilience than waiting for the next dam bond. Map suitable fields and basins, then pool beneficiary funding so growers are not the only payors. [Contact the team about aquifer recharge →](/contact?from=guide&topic=aquifer-recharge)

### if you invest

You are funding measurable underground storage and flood-risk reduction on working lands — classic under-financed natural infrastructure. Start at [/specific](/specific?from=guide) or [/general](/general?from=guide).

## frequently asked questions

### what is flood mar?

Flood-MAR (flood managed aquifer recharge) captures flood, storm, and snowmelt peaks on working landscapes, recharge basins, and floodplains so water infiltrates to the aquifer for later use — often more cost-effective than building new surface storage.

### which crops work for ag-mar?

It depends on soils and inundation tolerance. Alfalfa, pasture, and some permanent crops have been used in dormant-season pilots; many sites use dedicated basins instead of crop rows. Agronomic testing beats copying a neighbor's field plan.

### does on-farm recharge hurt the crop?

It can if timing, depth, or duration are wrong. Compatible systems and short, planned inundation windows are the point — this is managed flooding, not a failed irrigation event.

### is the recharged water "mine"?

Only under the banking, district, and water-rights rules that apply to your basin. Hydrology puts water underground; law decides who may recover it. See [groundwater banking](/guide/groundwater-banking).

## sources

[California DWR — Flood-MAR](https://water.ca.gov/Programs/All-Programs/Flood-MAR) — program definition and practice

[He et al. (2021), *Science Advances*](https://www.science.org/doi/10.1126/sciadv.abe6025) — Flood-MAR cost-effectiveness vs surface storage

[Kebede et al. (2024), *Hydrology*](https://www.mdpi.com/2306-5338/11/1/8) — MAR review; modeled Ag-MAR water-table recovery up to ~2.5 m/yr

[U.S. EPA — Aquifer Recharge and ASR](https://www.epa.gov/uic/aquifer-recharge-and-aquifer-storage-and-recovery) — U.S. practice context

[Managed aquifer recharge — series hub](/guide/managed-aquifer-recharge) — full toolkit map