3 Summary 



The Humboldt Bay jetties have experienced a long history of damage and sub- 

 sequent repairs since original construction was completed in 1899. Rehabilitations 

 were completed in 1911, 1927, 1932, 1939, 1950, 1957, 1963, 1971, 1988, and 

 1995. These rehabilitations consisted of the construction and/or installation of con- 

 crete monoliths, parapet walls, mass concrete, stone, concrete blocks, tetrapods, and 

 dolosse. Since the dolos rehabilitation of the heads of the jetties in 197 1 , damages 

 have been primarily along the trunk (stone) reaches of the jetties. No extensive 

 work has been required along the dolos fields since their construction. Prior to this 

 study, no sound, quantifiable data relative to the movement or positions of the dolos 

 concrete armor units had been obtained for the jetties. 



Under the current Periodic Inspections work unit of the Monitoring Completed 

 Navigation Projects Program, data from limited ground-based surveys, aerial photo- 

 graphy, and photogrammetric analysis have been obtained to establish very precise 

 base level conditions for the seaward dolos-covered portions of the Humboldt Bay 

 jetties. Accuracy of the photogrammetric analysis was validated and defined 

 through comparison of ground and aerial survey data on control points and targets 

 established on the structures. A method using high-resolution, aerial stereo photo- 

 graphs, a stereoplotter, and Intergraph-based software has been developed to ana- 

 lyze the entire above-water concrete armor unit fields and quantify armor positions 

 and subsequent movement. A detailed broken armor unit survey conducted during 

 the current effort has resulted in a well-documented data set that can be compared to 

 subsequent survey data. 



Now that base (control) conditions have been defined at a point in time and 

 methodology has been developed to closely compare subsequent years of high- 

 resolution data for the Humboldt Bay jetties, the site will be revisited in the future 

 under the Periodic Inspections work unit to gather data by which assessments can be 

 made on the long-term response of the structure to its environment. The insight 

 gathered from these efforts will allow engineers to decide, based on sound data, 

 whether or not closer surveillance and/or repair of the structures might be required 

 to reduce their chances of failing catastrophically. Also, the periodic inspection 

 methods developed and validated for these structures may be used to gain insight 

 into other Corps' structures. 



Chapter 3 Summary 



31 



