26 



the reinforced concrete columns bearing directly on substrata without pile supports, 

 and to the Koetitz pre-cast t\pe of slee\e protection for wooden pile protection. Atten- 

 tion was also given to the de\elopment of wharf design whereby' each a\ailable type 

 of substructural material could be used to best achantage. 



lip to this time the Bay region at the north, toward the great fresh water influx 

 from the Sacramento River, had supposedly been free of borer infestation. The Car- 

 cjuinez Strait territory had become extensi\-ely de\eloped by industrial and trans- 

 portation enterprises, and wharf construction had increased accordingly. All the 

 wharA'es were of untreated timber, portions of some ha\ing been built as far back as 

 1870, and all were apparently unmolested. 



The first discovery of Teredo navalis in the Bay came, as has been briefly related 

 in the introduction, in 1914 when a borer later identified as this species was reported 

 active in a structure at Mare Island. There was also some evidence that it had been 

 there in 1913. Subsequent demonstration that this borer could thrive in the brackish 

 water of the region and that conditions had long prevailed favorable for its attack 

 without such attack taking place, led to the conclusion that 191,^ was the year of its 

 arrival in the Bay. A period of higher rainfall (see chart, p. 37) in the next three 

 years — 1914 to 1917 — increased the fresh water river flow and reduced the salinity 

 in the upper Bay, killing off the borers or temporarily preventing further attack. 

 However, while the Teredo was thus checked in the northern territory, the infestation 

 spread to all parts of the Bay where higher salinities prevail, thus adding this borer 

 to the existing Baiikia and Limnoria infestations. Structures in those regions were by 

 this time, for the most part, built of protected piling, so that the coming of the teredo 

 had no marked effect. 



The year 1917 was one of low rainfall and the salt water of the Bay once more 

 advanced up the northern tributaries. This condition was further accentuated by 

 the withdrawal of large quantities of ri\'er water for niuni(ii)al supplies, for rice culture 



Fig. 12. I'ntreated ferry slip fender piles in Carquinez Strait destroyed by teredo, 1919. 



(5. P. Co. Photo.) 



and for general irrigation projects which had developed in recent years. Renewed 

 teredo attack was soon reported at Mare Island, hut little attention was given to it 

 elsewhere. This apathy was largely due to the fact that no trouble had been experi- 



