Layout 



The Colorado River navigation channel between its mouth and the GIWW is 

 10.5 km in length, 4 m deep and 300 m wide. The channel entrance to the 

 Gulf of Mexico, which is protected by a pair of rubble-mound jetties, is 

 5 m deep and 60 m wide. All elevations, unless otherwise noted, refer to 

 U.S. Army Corps of Engineers mean low tide datum, which is 0.43 m below 

 National Geodetic Vertical Datum (NGVD). The jetty system includes a 

 300-m-long weir on the northeast side of the entrance channel and an 

 impoundment basin adjacent to the weir to trap southwesterly moving littoral 

 material. The impoundment basin was constructed to allow for subsequent 

 sand bypassing to the downdrift beaches of Matagorda Peninsula. Figure 2 is a 

 plan view of the jetty system and impoundment basin. 



Other inland features included in the MOCR federal project were not 

 monitored by the MCCP. Diversion feamres include a channel and dam 

 located just south of the GIWW and Colorado River intersection which are used 

 to divert the flow of the Colorado river into Matagorda Bay, and a low-sill weir 

 across the Tiger Island Channel to prevent increased saltwater intrusion in 

 Matagorda Bay (see Figure 1). In May 1991, a dam was constructed across 

 Tiger Island cut that closed communication between the Colorado River and 

 West Matagorda Bay. The diversion canal which shunted the entire flow of the 

 Colorado River into West Matagorda Bay was completed in July 1992. The 

 diversion features were primarily built to provide for a separate flood discharge 

 channel to reduce flood damages along the lower Colorado River charmel. 

 Additionally, these feamres were constructed to introduce fresh water and 

 nutrients into Matagorda Bay to increase the commercial seafood catch from 

 the bay system. Other features of the MOCR federal project at the river's 

 intersection with the GIWW include a harbor, a turning basin, and two 

 recreation areas. 



Jetty and entrance channel design 



The entrance channel and rubble-mound jetties were designed as a straight 

 extension of the existing river channel into the Gulf. The seaward ends of the 

 jetties are spaced about 400 m apart for adequate protection of the entrance 

 channel and accommodation of any future chaimel enlargement. The northeast 

 jetty extends about 120 m from the dune line to the shoreline and has a crown 

 elevation of -1-2.4 m. At the shoreline, the jetty crown elevation drops to 

 4-0 m, to form a weir section, which extends 300 m into the Gulf. At the 

 seaward end of the weir, the jetty crown is again at -1-2.4 m to provide an 

 emergent end to the jetty. This outer section of the jetty extends to about the 

 3.7-m depth contour and is slightly angled to act as a breakwater for the 

 impoundment basin and entrance channel. Cover stone on the northeast jetty 

 ranges in size from 3.6 to 5.5 mt at the landward end to 14.5 to 16.3 mt on the 

 outer section. The southwest jetty was built based on a conventional design to 

 prevent northeasterly moving littoral material from entering the navigation 

 channel and provide a protected entrance for small craft during infrequent 

 periods when waves approach from the southwest. The southwest jetty has a 



Chapter 2 History 



