swamp marsh bog fen morass slough marshland wetland mire quagmire moor swampland muskeg wash quag slew moss bayou fenland everglade glade quicksand holm sump mud salina saltings bottoms polder everglades bottomland carr marish lowland wetlands bogland peat estuary marshes fens valley hollow gorge ravine canyon gap pass hole dale gully vale basin dell dene kloof depression notch glen trough combe channel clough dingle coulee slade cwm nullah strath rift coomb vega wadi bottom plain defile flume dip gulf couloir gulch gill saddle col linn concavity arroyo sinkhole chasm pit indentation crater excavation bowl cut abyss quebrada barranca crevasse dent sink