a. Northward relocation will provide safer navigation by increasing the distance 

 between the MSC-GIWW intersection, thereby putting it in area of weaker along- 

 channel and cross-channel currents. 



h. The relocated GIWW will not receive the significant contribution to sediment 

 shoaling experienced at the present location. Weaker currents across the 

 relocated GIWW will reduce the sediment shoaling rate as compared to the high 

 rate at the present location of the GIWW. 



c. Once the sediment-transport processes are known, rebuilding of a "New 



Simdown Island" might be accompUshed to create a more stable bird island that 

 win require less maintenance because it would be in an area of weaker currents. 

 The island would be placed at a location where it would not erode into the 

 GIWW, as is the case at present. 



The northward location would require minimu m dredging because of the existing 

 depths of the natural bay bottom to the north. 



No study has been undertaken to develop objective information for moving the 

 GIWW or for considering other alternatives to reduce dredging frequency. The problem 

 addressed in this DMS application is to determine the causes of shoaling at the present 

 MSC-GIWW intersection and to provide guidance for optimal placement of dredged 

 material at the alternative location of the GIWW. This information enters the decision 

 process forjudging the economic and enviroimiental feasibUity of moving the GIWW 

 northward to its pre-1942 location or for comparison to other possible alternatives. 



Objectives and Procedures of this Study 



The objective of this study is to determine the cause of chronic shoaling in the 

 GIWW near the MSC-GIWW intersection in Matagorda Bay and to recommend a 

 solution that wiU reduce the fi-equency and cost of dredging, while improving navigation 

 safety. The objective is to be met by application of DMS concepts and methodology. 



The procedure employed in this first DMS appUcation is as follows: 



a. Make site visits, review the existing hteramre, and discuss the physical processes 

 with those possessing local knowledge. Persons consulted were staff of the 

 Construction and Operations Division of the Galveston District, surveyors from 

 the Corpus Christi Field Office of the Galveston District, pilots of Matagorda 

 Bay Pilots Association, and Mr. Chester Smith, who is the Sundown Island 

 warden for the National Audubon Society. 



h. Make Umited-dmation measurements of the current and water level in the 

 vicinity of the MSC, Pass Cavallo, and the MSC-GIWW intersection to 

 understand the circulation pattern at the smdy site and to calibrate the numerical 

 hydrodynamic model estabUshed for Matagorda Bay under DMS guidelines. 



c. Analyze dredging records for the smdy site and interpret them in hght of 

 information obtained in Items a and h through classification according to the 

 DMS Manual (Kraus et al., in preparation). 



d. EstabUsh and calibrate a numerical hydrodynamic model for the depth-averaged 

 two-dimensional circulation in Matagorda Bay and run the model with the 

 existing condition and for the alternatives. 



Chapter 1 Background and Problem Statement 1 1 



