swale 
(swāl)
(swāl)n.
1. A low tract of land, especially when moist or marshy.
2. A long, narrow, usually shallow trough between ridges on a beach, running parallel to the coastline.
3. A shallow troughlike depression that carries water mainly during rainstorms or snow melts.
[Perhaps from Middle English, shade, perhaps of Scandinavian origin; akin to Old Norse svalr, cool.]