A- 8 



Erosion and siltation constitutes a significant problem for the 

 Bay region. The earth lost from the land to the Bay has hurt the farmers 

 who need the soil for their crops, the shippers whose vessels must 

 navigate shoaling channels, and the fishermen whose aquatic harvest 

 is being stifled and lost. 



Evidence derived from early charts and maps, from historical 

 documents, and from field studies and borings indicates that the rate 

 of sedimentation in different portions of the Chesapeake Bay has varied 

 over historic time. Prior to settlement by colonists and the initiation 

 of land clearing and agriculture, rates of sediment contribution from 

 land under forest cover were perhaps on the order of 100 tons/sq.mi. /yr. 

 However, with the advent of extensive clearing for agriculture, these 

 rates rose rapidly to values of 400 to 800 tons/sq.mi. /yr. As early as 

 the latter part of the seventeenth century visitors to colonial America 

 noted both the erosion of the fields and the muddy character of the 

 freshets. In addition, they observed the rapid siltation taking place 

 in a number of the early colonial harbor and river towns (State of 

 Maryland, 1968). 



The Potomac and Susquehanna Rivers transport the major sediment 

 loads deposited within the Chesapeake Bay system. The sediment con- 

 tribution of the Susquehanna is considerably moderated by the hydro- 

 electric dams between Harrisburg, Pennsylvania, and Conowingo, Mary- 

 land, in that these reservoirs trap a significant amount of sediment 

 moving downstream. The Susquehanna watershed is estimated to supply 

 some 600 thousand tons per year, or approximately 23 tons per square mile. 

 The largely unregulated Potomac River Basin, on the other hand, con- 

 tributes an estimated 2.5 million tons per year to the estuarine 

 system. This is approximately 170 tons per square mile (Corps, 1970). 



The fact that each tributary entering the Chesapeake Bay deposits 

 the bulk of its sediment load in the vicinity of its entrance to the 

 Bay constitutes an obvious economic "fact of life" for the economy of 

 the Bay itself. Perhaps the most striking illustration is provided 

 by the Potomac and the Anacostia Rivers in the vicinity of the nation's 

 capitol where channel improvement and dredging operations have been 

 virtually continuous since 1804. Much of the land adjacent to the 

 river including Haynes Point, the parkland along the Anacostia River, 

 and the National Airport are all made of sediments dredged from the 

 rivers. It is estimated that the annual cost of dredging on the 

 Potomac is on the order of $150,000 per year (State of Maryland, 1968). 



Recently it has become evident that increasing urbanization and 

 accompanying construction activities on the landscape may contribute 

 immense quantities of sediment to local areas. It is estimated that 

 of the million tons per year in the Potomac at Washington, approxi- 



