Sandplain lends itself to different drainage solution

The Central Coast Council media release quoted in Peninsula News "Everglades catchment drain upgrade completed" 29 April , tells us the upgrade "focussed on the section of drain that stretched from Carpenter St. to Glenn St" - fully 60 metres.

There are two sediment pits on Carpenter St and one on Glenn St.

From the Carpenter St. pit, there is a short pipe of around 40 metres to the open channel

I may be reading this wrongly, but half a million dollars seems a bit of an overspend.

If this figure is correct, what will it cost to implement future stages that "are currently in the design phase." And this is just the Everglades precinct.

On the positive side, at least Council is pushing the water in the right direction to Correa Bay, not the beaches.

Helpfully, Council's director tells us that this part of Umina Beach is "very flat" and that "flooding is often caused by build up of sediment in the drainage system that causes blockages."

There is an alarming problem with Council's thinking here.

This great flat sandplain lends itself to a different solution.

Most recent council drainage works have focused on directing all water to the Ocean Beach main drain with disastrous erosion consequences at the beach.

Modern thinking is to see cities as sponges and return excess and stormwater to the ground water system.

This "sponge" system requires little maintainence and is simple to install, especially when you have a sand base to act as sponge as we do.

Plumbers on my street were installing an absorption system last week on a new building and they do it frequently.

During the recent attempt by Council to flog off vacant blocks of land (local parks) it was put by several objectors that some of these blocks could be used as infiltration ponds.

Council's own consultant also had design plans for "trench drainage systems" that utilized "hydrophilic geotextile" matting coupled with structural lightweight void fill boxes to facilitate the transfer of stormwater to the groundwater system.

A company called Atlantis (atlantiscorp.com.au) supply these innovative systems. Look them up.

Umina and Ocean beaches had substantially rebuilt themselves before the storms in late May and early April.

The first storm took nearly a thousand cubic meters from just the Ocean Beach main drain outlet and the Ettymalong creek opening to Umina beach; and every small shower further eroded the beach until today it is a total mess.

The mayor is quoted: "This project is a great example of council delivering an innovative solution that makes a real difference to the lives of our community."

To my knowledge this tiny system hasn't been tested yet.

The next big rain event will be a test. It will also further erode our beaches.

I also dispute that this system is in anyway innovative.

Sediment traps are as old as agriculture.

The ancient street drainage, which existed on the Peninsula before the destructive kerb and guttering, incorporated open drains and sediment pits with some piping.

These old systems still exist in some parts of Umina.

They are identified by concrete pads sitting on bricks to raise them above the pits.

The concrete lids are too heavy to be removed manually and the street water is absorbed into the sand with excess flowing into the opening on each side, simple, efficient and the lids can be removed for cleaning out the sediment.

Your article concludes "Future stages of the Everglades catchment drainage project are currently in the design phase."

Let's hope the city's drainage engineers try burying their heads in the sand.

They couldn't do worse, and they might learn something.

Email, 9 May 2019

Bryan Ellis. Umina.