Greenseams — Milwaukee's Flood-Storage Land Protection Programme (USA)

Greenseams is a flood-management programme run by the Milwaukee Metropolitan Sewerage District (MMSD) with The Conservation Fund. Since 2001 it buys land, or permanent conservation easements, from willing sellers in the Milwaukee, Menomonee, Oak Creek and Root River watersheds, targeting wetlands, floodplains and vegetated corridors on water-absorbing soils so that they keep absorbing and holding stormwater rather than being paved.
The Conservation Fund reports more than 6,100 acres protected across roughly 167 properties, estimated to hold about 3.3 billion gallons of floodwater, with benefits reaching over 1.5 million people in the metro area. About 29,000 acres in four counties were identified as acquisition prospects. An earlier report cited a ~$24 million investment for almost 5,400 acres, mostly via easements and over 3 billion gallons of capacity; an MMSD official has argued that about 3 billion gallons for ~$30 million is far cheaper than engineered storage.
Caveats: the storage volumes are capacity estimates derived from soil and wetland properties rather than measured flood reductions, acreage and spending figures differ between sources and dates, and no independent evaluation of avoided flood damage was found. Biodiversity and carbon co-benefits are plausible but not quantified.

Read the full analysis: https://www.conservationfund.org/our-impact/projects/greenseams-milwaukee/