What is Abbreviation for decameters?

deca- (da-)a metric prefix meaning 10, derived from the Latin Word for ten, decem. The Greek form deka- is also used, and it has the advantage of avoiding confusion with deci-, one tenth. The International Bureau of Weights and Measures (BIPM) specifies deca- for the prefix and da- for the symbol. In its interpretation of the International System (SI) for U.S. use, the U.S. National Institute of Standards and Technology (NIST) recommends deka- for the spelling of the prefix. Following NIST, this dictionary uses the spelling deka-.

http://www.unc.edu/~rowlett/units/prefixes.html

dec·a·me·ter or dek·a·me·ter

(děk'ə-mē'tər)

n. Abbr. dam or dkm

A metric unit of length equal to 10 meters.

http://dictionary.reference.com/browse/decameter%27s?jss=1