A series of cascading basins is excavated along a sloped floodway typically established between adjoining agricultural fields. These basins address problems of stormwater runoff from agricultural lands and certain urban areas where runoff carries sediment, nitrogen, phosphorous and other pollutants into nearby streams, rivers and tidal waters, The cascading basin series begins with basin placement at a higher topographical elevation, followed by basin positioning downwardly along a natural or excavated floodway slope simulating a terraced effect. As upper basins are filled they spill over into basins therebelow. Angular features of basin exit grade and stormwater escape slopes retard egress of stormwater. A lowermost terminal basin includes sand berm, boulders, rip rap and other barriers to retain the polluted runoff. Basins may include vegetation, slag stone layers, and other pollutant treatment elements.