SEA- WATER SYSTEM, UNIV. OF CALIF,, SANTA BARBARA 



145 



lowed the final connection to the rigid 

 asbestos-cement pipe line. Bolted flanges 

 were used on these field connections to 

 further speed the installation. 



Whereas this filtering system borrowed 

 some of the characteristics of the rapid 

 sand filter used for industrial and munici- 

 pal water handling, the controlled condi- 

 tions under which a rapid sand filter is 

 backwashed and maintained w^ere consid- 

 ered impossible to attain in a varying tidal 

 zone situation. It was therefore deter- 

 mined to establish a rate of flow which 

 would be so slow that the dirt absorption in 

 the filter would be negligible. By utilizing 

 this reduced flow it was assumed that air 

 bubbles which result from the negative 

 pressures developed in high-rate filters 

 would not collect to halt the flow. In a 

 small test filter model 1 foot thick it was 

 observed that the rate of water flow 

 through local beach sand was slightly over 

 1 gallon per minute per square foot under 

 a head of 1 foot. Knowing that there 

 would be tidal heads of up to 8 feet over 

 the filter, which would increase its effi- 

 ciency, a design rate of 0,65 gallon of water 

 per square foot per minute appeared safe. 

 This rate has been maintained for 4 years 

 of operation with no evidence of a de- 

 crease. 



The only apparent explanation for the 

 lack of servicing demanded by this system 

 is its location in the surf. It is situated 

 at a point where there is nearly always 

 a strong tidal action and constant move- 

 ment of sand over it. This sand move- 

 ment, it is believed, has served as an auto- 

 matic filter-cleaning device. The first 18 

 inches of beach sand immediately cover- 

 ing the unit is thought to remain rela- 

 tively undisturbed except for heavy storms 

 of a severity which is expected only once 

 in several years. The sand above this 

 point is known to be constantly shifting 

 under the normal movement of the surf. 



Although it was assumed during the 



system's design that the shifting of the 

 beach sand would help maintain the filter- 

 ing qualities of the unit, it was also pre- 

 sumed that the periodic replacement of 

 the surface material would be relatively 

 inexpensive if trouble developed. A 

 south-coast oil refinery sea-water intake 

 system which utilized a beach-sand filter 

 operated successfully for about 2 years 

 before becoming sealed up by accumula- 

 tion of organisms in the sand above it. 

 This unit, which was nonportable, was 

 located near the shoreline where there was 

 only an occasional tidal flow over it. It 

 depended largely on lateral infiltration 

 through the sand. It was reported to have 

 been maintained in operation after the first 

 stoppage by a periodic chlorine sprinkling 

 treatment of the sand over the filter. In 

 anticipation of such a development the 

 UCSB installation was provided with a 

 connection to the campus domestic water 

 system. It was assumed that a fresh- 

 water back-rinse would help control such 

 growths. None have been detected to 

 date, and the sea water in the laboratory 

 is to all intents and purposes plankton 

 free. 



The choice of a pumping system as in 

 the case of the filters was determined in 

 part by the limited finances available. The 

 most economical installation on a first-cost 

 basis was considered to be a jet-pump 

 installation. This system consists of a 

 high-head centrifugal pump energizing a 

 venturi which creates the negative head to 

 draw up the ocean water. The centrif- 

 ugal pump operates in a loop arrange- 

 ment. It draws its water from the head 

 tank, discharges it through the venturi 

 back into the head tank. For each gallon 

 of water pumped through the venturi 

 approximately 1 gallon of fresh sea water 

 is drawn in from the ocean and discharged 

 into the head tank. The head tank holds 

 2,000 gallons of sea water which will nor- 

 mally supply the laboratory and the re- 



