Effects of high‐magnitude floods on channel form: A case study in Maryland Piedmont

Abstract

Four major floods occurred in the Patuxent River basin in the Maryland piedmont during the summers of 1971–1972. High flows of August 3–4 and September 11–12, 1971, caused by thunderstorms were of 50‐year and over 100‐year recurrence intervals, respectively. On August 27, 1971, a nearby storm brought bank‐full flooding and tropical storm Agnes again produced floods well over the 100‐year level on June 21–22, 1972. Record discharges on the Patuxent and its tributary, the Little Patuxent, were recorded on September 11, 1971, and June 22, 1972, respectively. Among the more striking effects were destruction of floodplain vegetation, widening of stream channels, and clearing of the channels of all but very coarse materials. Low and medium flows succeeding each flood reduced enlarged channel widths by building up bar remnants with fines and forming new bars along channel margins, tending to destroy the evidence of such floods. Channels preserve flood‐originated forms when high‐magnitude floods occur with sufficient regularity.