Seawater intake systems and outfalls, seawater intake velocity cap, the InvisiHead, it is the ultimate friend of the ecosystem and the environment

          The Elmosa AES Seawater Intake & outfall environmental-friendly Systems in Detail



Worldwide distributors 



bullets Introduction 
bulletOpen Water Systems 
bul Elmosa Offshore Intake System
bFlow Phases 
....b Approach 
....b Stabilization 
....b Acceleration 
....b Steady State 
bOutfalls and Wastewater Disposal 

Low velocity seawater intake system, the InvisiHead. More system improvement and sediment inflow protection and marine growth prevention.


In the light of the global warming and increasing pollutants reaching the shores of the seas around the world the state of the ecosystem has changed a great deal over the last four decades. It has become unsafe to install onshore open intake systems without investing heavily in equipment to safeguard uninterrupted flow. Going offshore and drawing the water from hundreds of meters away from the shoreline has become necessity more than a viable alternative. Wave action effects onshore are more pronounced than in offshore locations. However, inferior designs of the upstream inlet of the intake pipelines can lead to creating high negative pressures at and around the inlet, which will result in the suction of sand, fish, seaweed and other debris. 

The inlet has to be proactive in design and not reactive. Wedge wire screens for example do not reflect a system that is specifically made for seawater intakes. They are reactive and need a great deal of backup to remain in operation.  They may seem passive but truthfully with all the active support they must have to remain in operation they are indirectly very active. They are operation and maintenance intensive. They have to be frequently backwashed and air purged to push away the impinging marine life and debris. Most of the backwashed and purged material returns to the screens along with fresh supplies soon after the backwash pumps and air purging compressors are turned off. The backwashed and purged material is not drained away but a large part of it would come back under the effects of local marine currents and screen suction

The AES Elmosa proactive technologies work in concert to eliminate sediment, debris, and marine life inflow. The technologies include:
  • The InvisiHead, a hydraulically invisible seawater intake head system fitted to the upstream intake pipeline inlet located offshore. It is made of durable and robust material. The InvisiHead applying negligibly low suction forces drastically reduces the inflow of debris. It is hydraulically tuned in the lab to smoothly guide in flow streamlines moving toward the InvisiHead in a 3-D fashion funneling in from a 360-deg space surround the intake structure. The part of streamlines originating at the sea floor takeoff with a super slow velocity that is less than 0.002 m/s (0.0066 fps) and start moving toward the InvisiHead entrance. The sea floor take off velocity is too low to disturb the local community including silt and fine sand grains. The InvisiHead entrance dimensions are not calculated as usually done in standard intake inlets and velocity caps but experimentally determined as the flow is tuned in. That makes the design flow entrance velocity not to exceed 0.09m/s (0.295 fps);
  • The entrance dimensions are not calculated as usually done in standard intake inlets and velocity caps but experimentally determined as the flow is tuned in;
  • The NatSep Sediment and Debris Separation Basin is located onshore to perform natural separation of sand and debris during rough weather conditions if full mixing of the entire depth of the water column at the InvisiHead location where sand and seaweed may get carried through. The NatSep plays a complementing role by naturally separating sand and debris

3-D slow approach


Open Water Systems

Limited configurations and designs of open seawater intake systems are used in the industry. Cooling water intakes can be divided into two types: Open channel and offshore pipe systems.

Open Channel Intakes

The open channel type of intake system used to be the most common, usually located on the shore of a water body. This kind of intake system is usually made of a conveying concrete channel. Simple and complex mechanical screening systems are always included in these types of intake systems. The size and complexity of the screening system depend on the quantity and type of the suspended matter present in the water and on the quality of water. This type of system works with an acceptable degree of performance when small loads of debris are present and. The screening systems become ineffective when the water gets saturated with large loads of debris and sediments such as weeds and sand. The open channel system is going under a phase out on a global scale in favor of the more advanced and effective offshore system. The Open channel systems are currently under elimination due to their drastic adverse environmental impact on marine life.

Offshore Systems

The offshore type of intake system is currently the most common. The offshore distance and depth where the inlet should be located is decide by the following factors:  
    the topography of the floor of the water body ,
    the ground type criteria of the intake site of both of its onshore and offshore segments,
    the size of waves and depth of wave disturbances,
    tide variations,
    local environmental regulations, and
    weed concentration and movement patterns.

Dead weeds - their concentrations and especially their patterns of movement - are the most difficult factor to deal with. The buoyancy of weeds varies according to ambient and atmospheric conditions. Dead weeds travel over the whole range of the water depth while they are carried over under the effect of marine currents. Therefore, the prediction of their movement patterns is almost impossible, especially when the submarine current conditions vary with the water depth. 

The problems involved with offshore systems are similar to those of the open channel, but with less severity and lower frequency. Traveling screens in basins onshore are still required and intake head cleaning has to be performed regularly. Large quantities of marine life including fish, fish larvae and small live organisms however are harmed in the process of the intake system operation and maintenance. These are part of the reasons led to the development of the InvisiHead back in 1982. The InvisiHead has gone through frequent improvement ever since. 

There has been a wide range of submerged intake designs and layouts, all aimed at reducing approach flow velocities to help control and reduce the inflow of debris but suffer from excessive level losses and reduced flow rates caused by impingement of seaweed and Zebra Mussels which stick to wedge wire screen tees and sections in large numbers. Very few systems are designed to limit the impingement and inflow of fish, seaweed or marine vegetation, sand, and other suspended matter, which are the main concern among others of the Elmosa Intake System.


The Elmosa Offshore Intake System


Elmosa Offshore Seawater Intake systems consist of:

  • The InvisiHead: The InvisiHead is positioned at the upstream end located between 50 to 10,000 meters offshore from the shoreline. The offshore distance depends on the site conditions and the requirements of the user. The depths of the of the upstream end where the InvisiHead is to be located range between 2 and 50 meters or deeper.
  • The intake pipeline - the pipeline connects the InvisiHead with the NatSep separation basin located onshore. We configure the intake and discharge pipelines to be self cleansing applying the Elmosa Velocity Envelope (EVE) principle.

HDPEintake-pipe GRP

  • The NatSep separation basin - whatever sand and debris that may flow into the InvisiHead get naturally separated and settle at the NatSep intake basin storage area. The flow reaching the pumps is clean and free of sand and debris. Cleaning of the NatSep basin is done once or twice every 5 year. Elmosa has discontinued the use of all mechanical screening systems including stationary and traveling screens which are no longer needed.


InvisiHead Intake Head System - the backbone of the process

After years of research and development the InvisiHead system has been optimized and produced. The system is virtually hydraulically invisible to suspended mater including fish, fish larvae, sea floor sand, seaweed, and debris. It is engineered to control and drastically reduce the inflow of debris, the ingress of fish, mussels and other marine life, and entrained air. It is ideal to be also installed in areas designated as fragile and critical such as spawning grounds or special habitats. By utilizing the continuity equation and the potential flow theory we developed this system. These two hydraulic principles have been used as the main tools for flow calculations and system design optimization. The system also makes use of the natural laws in its operation. Gravity is the only driving force of the flow into the InvisiHead Intake Head System. The InvisiHead structure is robust and stable. It is made of relatively thick plates of Duplex or 316L stainless steel. It is anchored to a heavy concrete block buried in sea floor via sturdy support legs that keeps it stable to remain in full operation even under hurricane G force conditions years 


The system is less expensive and more economical than the conventional systems. Unlike the O&M-intensive wedge wire screens and other seawater intake systems, the InvisiHead is a proactive self-reliant system that actually makes money in the form of O&M cost saving. It requires no backwash or air bursting. No pumps, compressors or sensors during operation or any electronic, mechanical, or manual interference. It pays back its purchase costs in a short time.
The InvisiHead can also serve as a superb industrial effluent outlet by which the effluent flow can be dispersed in a way that it inhibits the fluid from sinking to the floor such as the case in RO brine discharges or rising to the surface such as in power plant cooling water discharge or municipal sewage or fresh water releases. 
Many intake systems have either proven to be very costly to build, operate, and maintain; or have involved a great deal of guesswork that produced less than optimal results. Offshore intake systems can be upgraded and highly improved by installing the InvisiHead. It can easily be fitted to existing intake pipe inlets. It is a balanced and well-designed intake head system. It fully utilizes the potential flow principle in guiding water particles into and through it in the form of smooth, uniform streamlines. The flow into the InvisiHead system goes through four flow phases: 

  • Approach                       
  • Stabilization 
  • Acceleration
  • Steady Flow

Super smooth flow transition from one phase to the next leads the flow through into the pipeline upstream end. Such a process made the head virtually invisible in hydraulic terms to suspended matter.  There where the InvisiHead borrowed its name. 


1. The approach phase:

Water particles start to move toward the Intake Head from all directions surrounding it at a velocity of << 0.002 m/s (0.0066 fps) about 5 meters (16 ft) away from the Head entrance. The velocity rises to 0.03 m/s (0.1 fps) one meter (3 ft) away. The final entrance velocity is 0.09 m/s (0.3 fps) max.  Natural currents generated by thermal and density differentials, tend to have velocities higher than these approach and entrance velocities. The controlling velocities at the ambient are those of the marine currents and not those initiated by the InvisiHead flow effects. The pressure drop around the InvisiHead due to the suction caused by the head deferential at the intake settling basin located onshore is thus negligible, and does not disturb debris or cause it to travel toward the InvisiHead. This makes the InvisiHead virtually nonexistent as a sink point, and thus it becomes hydraulically invisible to suspended matter.

2. The stabilizing phase:

This phase extends from the lower or upper part of the InvisiHead entrance depending on the location of the intake pipe inlet and ends at the InvisiHead post outlet. In this phase the flow proceeds smoothly at about 0.11m/s (0.33fps) toward the InvisiHead outlet and eventually to the intake pipe inlet and accelerates to reach steady state. That is the ultimate velocity of the flow prevailing inside the intake pipe. The phase-to-phase transition velocities are lab tested and predetermined to provide smooth flow transition and to eliminate any potential for eddies or vortices, thus reducing pressure losses and in turn allowing the use of smaller intake pipes and shallower onshore pump intake basins since the depth needed for the settling basin onshore would also be reduced due to the reduction of the differential head required at the settling basin to drive the needed flow capacity.  This phase covers the internal approach portion of the InvisiHead, the perforated area of the guiding vanes. In this phase water particles move freely throughout the entrance ports of the InvisiHead and through to the opposite end. In this phase multi directionality of the flow overrides the radial flow due to the unlimited access to marine currents thus the actual flow goes out of phase by 90. In effect, this process enhances flow flexibility and stability by allowing velocity of horizontal currents to override velocity of flow toward the intake pipe inlet and diverts marine life, sediment and debris away from the actual flow and release the suspend matter at the ambient and back into the environment again. Access for flow streams created by wind, thermal, and density differentials is permitted through the upstream part of the InvisiHead and all the way through to the opposite end. In this phase more security against the flow of marine life, sediment, and debris into the InvisiHead is provided. In this phase the flow is smoothly divided and stealthily directed to the InvisiHead pre outlet and then into the post outlet/intake pipe inlet. Debris or fish that may enter the InvisiHead get flushed out through the opposite end of the InvisiHead into the ambient again and will not flow down into the intake pipe since the flow velocity at the InvisiHead pre outlet is lower than that is naturally prevailing at this phase. The velocity leaving the pre outlet is about 0.11-0.12 m/s (0.33-0.39 fps).

3. The acceleration phase:

This phase extends from the lower or upper part of the InvisiHead entrance depending on the location of the intake pipe inlet and ends at the InvisiHead post outlet. In this phase the flow proceeds smoothly at about 0.12m/s (0.39fps) toward the intake pipe inlet and accelerates to reach steady state. That is the ultimate velocity of the flow prevailing inside the intake pipe. The phase-to-phase transition velocities are lab tested and predetermined to provide smooth flow transition and to eliminate any potential for eddies or vortices, thus reducing pressure losses and in turn allowing the use of smaller intake pipes and shallower onshore pump intake basin since the depth needed for the settling basin onshore would also be reduced due to the reduction of the differential head required at the settling basin to drive the needed flow capacity.

4. The steady flow phase:

This phase begins at the downstream point of the InvisiHead and ends at the downstream end of the intake pipeline at the settling basin onshore. In this phase steady flow regime prevails. In this phase we utilize the Elmosa Velocity Envelope (EVE) to maintain a velocity range that keeps the flow inside the intake pipe to maintain a self-cleansing environment so that no sediments settle inside the pipe or marine life grow on the internal walls of the intake pipe as long as the low rate range is maintained.

The InvisiHead intake head dimensions are all based on the average steady flow velocity, thus a flow-tuned intake head designs and construction were made possible.  In standard practice, an entrance velocity is arbitrarily selected with a known flow rate. The area of the intake head opening is thus calculated using the continuity equation. Either the height or the diameter/width is assumed and then the other dimension is calculated. In the flow-tuned InvisiHead no assumptions are made during the design and sizing of the IH.  All values are calculated since they are all interdependent. 

The InvisiHead is designed to take either individual or multiple forms. This is always decided on individual basis. The InvisiHead can be retrofitted to existing intake pipelines.


The 4-D Spatial and temporal round surround sideways up and down multi time decay plume dispersing InvisiHead Outfall Diffuser System
 for Power and Desalination Plants, Oil Refineries, Mining and dredging industry,  Municipal
and Industrial Wastewater Disposal

Meets and exceeds US EPA standards and regulations
Dispersion of: Power plant cooling water; Desalination plant brine; Wastewater;  Dredging and mining slurry discharges and turbidity control; Produced water in offshore oil platforms; Petrochemicals, refineries, and aquaculture effluents.

The InvisiHead system works as an excellent offshore submarine outfall. It diffuses, disperses, and dilutes the discharged water in a round surround sideways up and down 360 degree single plume that is not allowed to sink to the sea floor in case of the RO brine or rise up to the surface in case of cooling water or municipal effluent release  - no potential for recirculation. The dispersed effluent mixes with the ambient seawater. In a short time and within the vicinity of the release point effluents assumes the same physical and chemical properties of the surrounding seawater causing no negative impacts on plant operation  or on the local environment. Mining slurries and dredged water when released through the InvisiHead diffuser  disperse, in a 4-D - spatial and temporal fashion - to mix and dilute and reach background turbidity levels within the early portion of the near field mixing zone and close to the diffuser. The same goes for produce water, power plant and refinery cooling water, RO desalination brine, municipal and industrial wastewater, aquaculture reject water, etc. The InvisiHead outfall performance meets and exceeds US EPA standards and regulations.

Outfall updated in 2012

The InvisiHead works as an efficient heat transfer system when used as a power plant cooling water outfall. It ensures adequate mixing and efficient heat dispersion to reach equilibrium a few meters away from the release point. The heat plume does not reach the surface and it is confined to the area close to the point source. Heat, TDS, or sewage sensors installed a few meters away from the outfall diffuser will register no change in their readings. Linear outfalls are no longer a necessity.



The InvisiHead is a hydraulically balanced simple system, free of any operating or maintenance needs and requirements or any spare parts. It contains no moving parts. This makes the AES Elmosa intake systems including the InvisiHead, intake pipeline, and the NatSep economically feasible and environmentally attractive. The system components function by positively utilizing the natural forces. In doing so, sediment flow is drastically reduced or even eliminated and pressure losses are minimized. System features include:  

  • Reduction of pipeline pipe diameters and settling basins size; 
  • Initial costs reduction;
  • No O&M costs are associated with the InvisiHead operation;
  • The InvisiHead does not attract aquatic life or suspended matter;
  • Applying the Elmosa Velocity Envelop (EVE) in the intake pipe configuration insures self-cleansing that prevents sediment settlement or biology growth inside the pipe;
  • Operation and maintenance works are eliminated since backwash of the intake pipes and InvisiHead is eliminated;
  • Settling basins are also cleaned less frequently due to the reduction of sediment inflow; 
  • No mechanical screens are attached to the InvisiHead or installed in the NatSep thus debris or Zebra Mussels if found have no negative impact on the intake system performance; 
  • Low InvisiHead approach velocity of 0.002 m/s max.; 
  • Low InvisiHead entrance velocity of 0.09 m/s max.; 
  • Low InvisiHead exit velocity of about 0.12 m/s;
  • Variable flow phases at the InvisiHead to: 
    • not to be attractive to aquatic life,
    • promote head loss reduction that results in: 
      • smaller pipelines, 
      • shallower intake basins, 
      • less debris inflow, 
      • the elimination of backwash and air bursts,
    • further reduce debris inflow, 
    • perform self-cleansing. 
  • Duplex or 316L SS construction; 
  • Long useful life of over 50 years;
  • Robust structure to ensure durability and intake system integrity;
  • No mechanical screens are used at any stage of the InvisiHead or the NatSep; 
  • Adaptability for use in effluent outlets and plant outfalls; 
  • Can be retrofitted to existing systems;
  • Can be used as natural and efficient pump strainer fixed in place of the pump suction bell;
  • Immune to oil spills; 
  • Low initial costs; 
  • No O&M costs are associated with the InvisiHead and by saving on O&M costs the systems pays back its capital costs in a short period of time.
  • As an outfall it works as a low velocity round surround 4-D 360 degree up sideways and down plume dispersion that decays rapidly and disappears into the ambient. It works great as a
Mining slurry diffuser
Dredging diffuser and turbidity control
RO desalination brine diffuser
Cooling water diffuser
Produce water diffuser
Treated sewage diffuser
Aquaculture used water diffuser.


American Eco Systems and Amecosys will be very glad to share their experience with their prospective customers. We at AES and Amecosys have the ability to solve your intake problems. The Elmosa offshore intake systems and the Infiltration are designed to serve the world over. The systems are environmental friendly, help biodiversity, and protect the ecosystem. Keeping a healthy environment is a top priority at Elmosa.

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