The use of principal component analysis for interpreting ground water hydrographs

Principal component anal sis was used to define patterns in water table hyd rographs at four small, lake-watershed research sites in the United States. The analysis provided insights into (1) characteristics of ground water re charge in different parts of the watersheds; (2) the effect of seepage from lakes on water table fluctuations; and f3j the effect of differences in ge ologic properties on water table fluctuations, At two sites where all of th e water table wells were completed in permeable deposits, glacial outwash i n Minnesota and dune sand in Nebraska, the patterns of water table fluctuat ion primarily reflected timing and magnitude of recharge. The water table h ad more frequent and wider ranges in fluctuations where it was shallow comp ared with where it was deep. At two sites where the water table wells were completed in sand or till, a glaciated mountain valley in New Hampshire and stagnation moraine in North Dakota, the patterns of water table fluctuatio ns were strongly related to the type of geologic unit in which the wells ar e completed. Furthermore, at the New Hampshire site, the patterns of water table fluctuations mere clearly different for cells completed in sand downg radient of a lake compared with those completed in sandy terraces on a moun tainside. The study indicates that principal component analysis would be pa rticularly useful for summarizing large data sets for the purpose of select ing index wells for long-term monitoring, which would greatly reduce the co st of monitoring programs.