Long-Term Structural Solution for the Mouth of Colorado River Navigation Channel, Texas

Abstract

This report describes a study performed for the U.S. Army Engineer District, Galveston, to develop a structural solution involving modified or new jetties in support of a reliable shallow-draft channel at the Mouth of the Colorado River (MCR), Texas. The site has experienced excessive sediment shoaling that has denied full project features to navigation channel users. The study took a multidisciplinary approach involving field measurements, shoreline analysis, numerical modeling of shoreline change and longshore sand transport, numerical modeling of inlet processes, and preliminary design of a new east jetty. The study concluded that the MCR was not performing as intended because (1) the Colorado River was diverted to Matagorda Bay in 1992 as part of an environmental restoration project, thus depriving the inlet of the river's discharge of water and associated scouring action; (2) the weir jetty system constructed over [1988][1989][1990] was too wide and the weir section too long; and (3) the sediment impoundment basin associated with the weir is dangerous for people wade fishing and allows sediment to be bypassed during times of high water.The solution obtained is to construct a new east jetty parallel to and 500 ft (152 m) from the west jetty. It is recommended that past bypassing practice be continued through dredging of the impoundment fillet expected to form on the beach adjacent to the new east jetty and placing that material on the west beach. The preliminary jetty design incorporates experience with jetties of similar size inlets along the Texas coast.

Inlet Stabilization: A Case Study at Mouth of Colorado River, Texas

“…Operational experience has since revealed the practical limitations of this technology, with most constructed projects being deemed unsuccessful. Actual longshore transport rates observed after construction were about twice as much as predicted in the 1977 GDM, requiring more dredging than anticipated to maintain a navigable channel (Kraus et al 2008). Further reducing inlet efficiency, the Colorado River was diverted back into Matagorda Bay in 1992 to restore water and sediment flow into the bay.…”

“…The new jetty project was completed in November 2010, shown in Figure 8 with recent shorelines overlaid. The design process, documented in Kraus et al (2008), resulted in a narrow and deep channel with a new east jetty 150 m east of and parallel to the existing west jetty. The new jetty was designed to be connected to the existing STS, and crest elevation of both the STS and landward portion of the new jetty were raised to reduce wind-blown transport of sediment over the structure.…”

“…Astronomical tides are often dominated by strong wind on the Texas coast; wind-dominated tides often result in the fastest currents through a Texas inlet, controlling its stability (Kraus 2007). Average wave height offshore is less than 1.5 m (Kraus et al 2008) with extreme waves during tropical storms The Mouth of Colorado River (MCR) is a federally authorized shallow draft navigation channel located in Matagorda County, TX. A weir jetty system was constructed at the MCR in the early 1980s to stabilize the inlet and provide access to the Gulf of Mexico.…”

“…After the raft was cleared in 1929, floods carried large volumes of sediment and logs into Matagorda Bay creating a delta across the Bay which connected to Matagorda Peninsula. This new configuration led to increased flooding of Bay City; to relieve flooding, a channel was dredged across the delta to the Gulf in 1934(Kraus et al 2008). Creation of the new channel, later to be named the Colorado River Navigation Channel (CRNC), was the first time the river had discharged directly to the Gulf in recent history.During preparation of the 1977 General Design Memorandum (GDM) for the original weir jetty system, net transport was estimated to be 230,000 m 3 /year to the west with negligible transport to the east (U.S. Army Corps of Engineers (USACE) 1977).…”

Numerical Investigation of the Impact of Jetties on Accretion Problem at Rosetta Promontory, Egypt

“…For instance, U.S. Army performed a structural solution involving new jetties at the Mouth of the Colorado River (MCR), Texas as the site has experienced excessive sediment shoaling. It is expected that this new jetty will be a permanent structural solution that would reduce dredging frequency while maintaining a reliable channel [13].…”