Intake Approaches

The primary objective of the intake is to supply seawater to the proposed  desalination facility.

Important considerations include source water quality, construction impacts, operational impacts to marine organisms, capital and maintenance costs, and regulatory permitting. 

scwd² is currently evaluating both subsurface intakes and screened open-water intakes.

• Subsurface intake advantages include:

  • Potential for natural filtration pre-treatment

  • Minimize impingement and entrainment issues

  • Minimizes growth of marine life on the inside of the intake pipeline

  • Favored by regulatory agencies

• Screened Open-Water intake advantages include:

  • Not dependent on local coastal and ocean floor geology

  • Can provide larger volumes of water at lower cost

  • Utilizes existing outfall pipeline to minimize construction impacts

Examples of Subsurface Intake Approaches

Source:  Kennedy/Jenks
Horizontal Collector Wells (Ranney)
Horizontal collector wells require similar conditions as vertical beach wells.

Source:  Kennedy/Jenks
Slant or horizontal wells could potentially work where vertical wells will not.

Source:  Kennedy/Jenks
An engineered infiltration gallery could work where natural ocean floor geology is not suitable

 

A 2001 report for the City of Santa Cruz concluded that beach wells and collector wells would not provide sufficient water and would be damaged in storm citing shallow beaches over bedrock, fine grained sands, significant seasonal beach erosion and San Lorenzo alluvial deposits have abundant organics, silts, and clay. 

There is an alluvial channel offshore of Santa Cruz that may support a subsurface slant well or infiltration gallery, and agencies have launched an evaluation on a subsurface/subfloor intake approach.  They are currently working with USGS to evaluate existing studies of local seafloor have engaged in an offshore geophysical study to evaluate the feasibility and costs of a subsurface intake.

Source:  Kennedy/Jenks

 

 Example of Open Ocean Intake

Offshore cylindrical wedgewire screen intake system

There is an existing 36-inch abandoned wastewater outfall pipe that extends approximately 2,000 feet offshore between Terrace Point and Point Santa Cruz (at Mitchell's Cove).  The abandoned outfall pipe may be a potential intake structure for the proposed desalination plant. 

 

Narrow-slot cylindrical wedgewire screens at the end of the intake system provide  fish/marine protection.  Below is a video illustrating a wedgewire screen system with 2mm screen size openings and an intake velocity of 0.5 feet/second (fps) and an ambient current velocity of 0.5 fps.  A properly designed screen system allows fish larvae to float by the intake as water is drawn through the pipe to a desalination facility.   

Source:  Electric Power Research Institute and Alden Research Laboratory