Glacial Outwash

Glacial outwash occurs south of the moraines as a broad, relatively flat plains.   Soils formed in glacial outwash or in contrasting materials over stratified sand and gravel are on outwash plains.  Slopes are generally less than 3 percent.

A great amount of sorting and stratification generally is evident in outwash deposits.   The grains are almost all sand-size and gravel-size, and they are rounded, which is the result of water transport.  In general, the sandy or sandy and gravelly outwash materials are loose in consistency. 

The topography of outwash plains is such that most engineering works can be accomplished without extensive earthmoving operations.  Embankment for roads are generally constructed without difficulty.  The soils support high fills without excessive settlement.  As with glacial tills the settlement is through particle rearrangement and occurs quickly.  Highway gradelines generally at or near the existing ground surface on the outwash plains.  Because of the uniformity and roundness of the particles, trafficability for wheeled vehicles is often limited. 

The steeper soils that formed in outwash are along drainageways or outwash plains, as well as on moraines.  In places the lower slopes are more poorly drained, and Haven Loam, is in the bottom of drainageways.  As the shores or Long Island are approached; the internal drainage of the soils becomes poorer.  Internal drainage of the soils is also poor along the Peconic River Basin.  Excavations in these areas must be dewatered. 

Drainage of surface water on outwash plains is mostly by infiltration.  The porous soil readily soak up precipitation.  Glacial meltwater channel are now slight depressions in outwash plains.

Plymouth and Carver soils formed in sand, and they are too droughty to be used as topsoil.  Bridgehampton and Haven soils formed in silty or loamy deposits over outwash sand and gravel, and they are good sources of topsoil.  Fill material from outwash is good, but in places it lacks the fines needed to obtain the desired compaction.

Soil Survey of Suffolk County, New York. 1975
United States Dept. of Agriculture, Soil Conservation Service, in cooperation with Cornell Agricultural Experiment Station