Design and Performance of Four Evapotranspiration Caps

Abstract

The protective cap/biobarrier experiment was constructed to compare the performance of three alternative evapotranspiration (ET) caps with that of a U.S. Resource Conservation and Recovery Act recommended cap. One alternative cap configuration was a homogenous soil cap, while two additional alternative cap configurations contained biointrusion barriers placed at different depths within a soil profile. All cap configurations were planted with two vegetation types and were tested under three climate-change precipitation scenarios. Under ambient precipitation, the three alternative cap configurations performed similarly and returned all of the water received from precipitation to the atmosphere during each growing season, regardless of vegetation type. Growing season ET on ambient-precipitation caps ranged from 133 to 338 mm. Native vegetation extracted more water from caps under augmented precipitation regimes than did a grass monoculture. End-of-season soil volumetric water content was 1.7–5.9% lower on caps planted with a native species mix. When planted with native vegetation, the alternative cap designs tested here should easily meet United States Environmental Protection Agency equivalency criteria.