Pumphouse Project Update #3





The silt boom in place to protect the lake.

  

Perhaps the most difficult portion of the Pump house project is now complete.  The installation of the coffer dam, followed by the installation of the intake structure, and the removal of the dam took place over the last couple of weeks.  The following pictures and video will illustrated the process and the steps involved.  



The vinyl liner.

 

In order to protect the lake and the environment, it's necessary to take precautions against the project impacting the surrounding area.  A yellow silt curtain or silt boom surrounds the entire work area, and  keeps all free floating silt from creating a plume in the lake. To further reduce the chance of contamination, a two inch pump constantly draws water from the inside the silt boom, thereby creating negative pressure. 

The support structure of the dam is made up of hundreds of large, strong, permiable bags. Each bag contains roughly 3000 pounds of washed gravel. The bags are stacked in the lake three and sometimes four high to support a vinyl liner that acts as the actual water barrier. The liner is one continuous piece, 200 ft by 30 ft and must be unfolded as it is laid on top of the gravel structure. The excess of the liner is then draped down the lake side of the gravel bags, laid on the bottom of the lake and held in place with sand bags.  Then the contractors use two 6 inch pumps capable of pumping 1500 gallons a minute of water each to de-water the area.  Click on the link below to view the video showing the process from start to finish.

                                         http://www.youtube.com/watch?v=cGb0TTh04uc

Once the area is clear of water the contractors installed the intake beneath the lake floor, this ensures that the lake level will never drop below the intake. 



The intake waiting to be installed in the lake bed.  if you click on the photo you can see the holes cut into the pipe to allow the water to flow freely into the intake.





The intake after it has been set in place.  Note the filter cloth under the gravel to prevent contamination of the infiltration gallery.

Once the intake was installed the area is back filled with one inch clear gravel. The black filter cloth lines the side and bottom of the infiltration gallery and prevents the gravel from becoming contaminated with silt.  Why go to all this trouble?  There are two main reasons.  In the past we have been having issues with the water quality coming from the domestic intake (which feeds the clubhouse, the maintenance shop and the washroom on 12). With this new intake the water will be filtered by the gravel and thus removing most of the solids from the water.  The other reason is that the Department of the Environment

(DOE) requires that any intake from the lake must have a means to prevent fish from being sucked into the system.   The DOE determines that for the size of the intake pipe, and the rate at which the water is removed from the lake (in feet per second), must be under a certain level to allow the fauna to escape the draw into the system.   If we were using a open ended pipe, then a cage or fish screen would have to be built around the pipe large enough to reduce the speed of the water traveling into the system. With the size of our intake pipe, the fish screen would be massive, and because it has to be stainless steel, very expensive. The alternate idea was to make the intake area larger by dispersing the suction over a trident shaped cluster of pipe.  To further reduce the speed of the water, the intake structure is then buried in a gravel infiltration gallery.  This met the DOE's standards and kept our costs down.  

The installation is completed by covering the infiltration gallery with larger gravel, then a layer of river stone to keep the gravel in place and ascetically blend it to the shore.  The liner and coffer dam are removed and the the area inside the silt boom is left alone to settle.  The silt boom is then removed and the intake is ready to use.  

Currently we are waiting for Nova Scotia Power to complete the installation of the three phase power across the railroad tracks, which should take place in the next few days.  However, the transfer of the pumps from the old pumpstation the the new one won't take place until late fall.  Even though we have seen record amounts of rainfall this year, August and September are historically the hottest times of the summer.  To transfer the pumps during this time might put the health of the golf course at risk, which is a chance we're not willing to take.