Harwood (1973) discounts typical currents flowing through the pass as being capable of 

 creating and supporting either a permanent flood or ebb delta. The reasoning is that flood 

 and ebb deltas are not prominent at other inlets on the Texas coast, nor is a rehc ebb delta 

 found opposite Matagorda Peninsula, which would have been abandoned as Delcros 

 Point that migrated to the south in geologic time scales. 



The consequence of bearing for the present smdy is that clear empirical evidence 

 indicates a strong current issuing through an inlet or entrance in Matagorda Bay can 

 transport sediment and deposit it as far as 3 irules bayward of the inlet or entrance. 



Figure 3. Shrimp boat sunk in Pass Cavallo (September 1997) 



Tidal prism is defined as the product of bay water-surface area and the tidal range, 

 typically the spring tidal range. Harwood (1973) concluded that the cross-sectional area 

 of Pass CavaUo decreased after the Colorado River delta eliminated the water-surface 

 area of East Matagorda Bay from the bay system because of the decrease in tidal prism. 

 Her conclusion was based on estimates of the tidal prism and the cross-sectional areas of 

 Pass CavaUo as interpreted from navigation charts and a sateUite photograph (for the year 

 1971). She Usts six dates from 1856 to 1971 for which survey data were available for 

 study. By 1971, the discharge through Pass Cavallo had decreased as compared to 

 estimates from earUer dates. With diversion of the Colorado River back to Matagorda 

 Bay in 1992, this cause for a reduction in flow out of the bay was eliminated. 



More significantly, the discharge through Pass Cavallo has decreased because the 

 Matagorda Ship Channel (MSC) opened in September 1963, as also noted by Harwood 

 (1973). Ward (1982) compared measured tidal prisms of Pass Cavallo and the MSC 

 available from 1959 to 1976 and showed that the MSC had already capmred half the tidal 

 prism by 1976 (Van de Kreeke 1985). Measurements made in the present study, as 

 described in Chapter 3, show that three-fourths of the discharge or prism now goes 

 through the MSC. Pass Cavallo is closing, a situation considered in a physical model 



Chapter 1 Background and Problem Statement 



