I will be putting grey
water into mulch basins sized according to
Art Ludwig's book. Would putting an (empty) cold frame over them help to keep them infiltrating water during the winter? Here in Colorado the little snow we get in dry winters mostly sublimates off the surface, so recharging the mulch and soil during the winter would be helpful, especially for
trees. (Winter watering of trees and perennials is recommended here, since trees often dehydrate when the soil is frozen and the days are warm and sunny.)