The Atchafalaya River, a vener- 

 able distributary of the Mississippi 

 River, has a distinct gradient advan- 

 tage because of its shorter route to 

 the Gulf of Mexico. Aided by man's 

 activity, the Atchafalaya has rapidly 

 increased its proportion of the Mis- 

 sissippi's latitudinal flow to more 

 than 30 percent during this century. 

 The result has been the rapid devel- 

 opment of a new delta 130 miles (200 

 km) west of the modern Balize Delta. 

 The new Atchafalaya Delta is the 

 fifth major event in the 6,000 year 

 history of the delta system. The 

 delta is building into an area where 

 the effects of deltaic sedimentation 

 have been absent for over 2,000 years 

 (Frazier 1967). This region, tradi- 

 tionally characterized by shoreline 

 retreat, is experiencing a reversal 

 in the landloss trend and local shore 

 line progradation. 



Scientists at Louisiana State 

 University, Center for Wetland Re- 

 sources became intensely interested 

 in this delta-building episode be- 

 cause of the opportunity to study the 

 estuarine hydrodynamic, geological 

 and biological processes taking 

 place. Through a cooperative effort 

 with the Corps of Engineers, NOAA Sea 

 Grant and Naval Oceanographic Pro- 

 grams, active monitoring of delta- 

 building processes began in 1975. 



The purpose of this paper is to 

 address the development of the Atcha- 

 falaya Basin and the new delta, its 

 impacts, and possible management al- 

 ternatives to deal with these im- 

 pacts . 



ATCHAFALAYA BASIN DEVELOPMENT 



This new episode of delta build- 

 ing started about 1950 (Shlemon 

 1975), but since the initial delta 

 growth took place in the subaqueous 

 (underwater) environments of Atcha- 

 falaya Bay, there was little aware- 

 ness of this event during the first 

 twenty years of development. In 1973 

 definite subaerial delta lobes and 

 artifically created spoil islands 

 began to appear at Atchafalaya Bay 

 and by 1975, at the end of three con- 

 secutive high water years, in 1975, 

 the emerging deltas had grown to en- 

 compass several square miles of the 

 bay. 



Associated environmental and 

 engineering problems emerged quickly. 

 Fisheries were disrupted as sediment- 

 choked freshwater spread throughout 

 adjacent bays and marshes. Channel 

 shoaling impeded navigation on the 

 heavily used waterways near Morgan 

 City. Rapid changes in the flowline 

 also created alarming flood control 

 problems for Morgan City. 



The Atchafalaya River was a 

 distributary of the Mississippi as 

 far back as the 1500' s (Fisk 1952). 

 During the middle and late 1800' s, 

 flow from the Mississippi and Red 

 Rivers into the Atchafalaya was in- 

 creased by the removal of a log raft 

 and dredging of a navigation channel. 

 By the mid-1900' s a natural channel 

 had become so well established 

 through the diversion that the volume 

 of flow increased at an alarming 

 rate. Total capture of Mississippi 

 River flow seemed inevitable because 

 of the Atchafalaya' s shorter route to 

 the Gulf of Mexico and its decided 

 gradient advantage. Old River con- 

 trol structure, built in 1963, was 

 designed to prevent this possibility 

 by limiting the diversion into the 

 Atchafalaya to approximately 30 per- 

 cent of the flow of the Mississippi. 



Because the lower course of 

 the Atchafalaya River contained a 

 network of lakes and swamp catchment 



351 



