Rocks in the bunkers.

Hey folks,
Today is September 18 and I have been woefully neglectful of our maintenance blog.  I apologize for the delay and I will endeavor to increase the frequency of posts, keeping you folks more informed.

The results are in from our survey and  the overwhelming area of concern with regards to the maintenance department was the condition of the bunkers.  About 50% of the survey participants have stated that the bunkers meet the expectations for Oakfield and the other 50% surveyed disagreed with that statement.  In the comments section of the survey, people provide some insight as to why they felt the bunkers needed more work.   The rocks in the bunkers were a common concern and some folks were wondering where the rocks had come from.  I've done some checking and here's what we have found.
During the reconstruction of the green sites the base for the bunkers were created from the natural soil in the area.  While "clayish" in nature, the soil not as dense as actual clay and is susceptible to washing out.  Below is a typical wash out from about and inch and half of rain (on the back of 13 green).

Note how the material on the top edge of the bunker washes down to the lower portion of the trap. These are the fines that are washed from the edges of the trap and filtered to a silt when the water drains through the bottom of the trap. Below is a photo of the material under the sand.

This is the source of the rocks.   

When the staff is in the process of repairing the traps the initial steps are to remove the silt form the lower portion, and then shovel the sand back up and in to the washouts.  The piles are then raked out, but inevitably stones are mixed into the sand and float to the surface.  One way to mitigate the washouts are to add the liners to the bottom of the trap to prevent the fines and rock from contacting the sand.  In heavy rains the water can get under the liner and cause it to bubble and after a few years the liners rot and tear easily, finding their way to the surface and becoming another impedance.  

One of the other common complaints about the bunker s is that the sand is heavy in bottom of the bunkers.  This is also related to the washing out of the bunkers.  

The bunkers sand as it arrives, uncontaminated and stone free.

Bunker sand is naturally shaped to not compact, having particles relatively the same size and rounder in shape. A good analogy to explain this is to imagine a swimming pool filled with golf balls, the spaces in between the round balls would allow water and air to travel freely and compacting the surface would be difficult.  Now imagine the same pool with golf balls and sand poured over top. The sand would fill the voids between the balls and create a surface that is likely compact. This is the same effect that the fines have on the sand in the bottom of the bunkers, filling the gaps between the sand particles creating a denser material.  

So how do we fix the issues of stones and dense material? Theses two are clearly the result of contamination in the sand from washouts. Our first step is to identify the areas where the likely hood wash outs can be reduced. Here's an example.

The bunker to the left of number nine has a few areas where the ground leading up the edge of the trap is shaped in such a way the water will run into the trap from other surface areas.  These low edge areas will concentrate run off and increase the trap washing out.  By raising or installing drainage in front of the trap edge we should be able to redirect the water and reduce washouts.  These minor adjustments would be only be effectually on some of the traps, as the traps where the ground surrounding is too steep to alter upwards and would have to be adjusted differently. The green side bunker complex on number eleven is an example.

In the case where the ground surrounding is too steep to raise the edges and change the direction of water flow, we could reduce the "flashing" or height of the sand trap edge and thereby reduce the steepness of the sand, making it less likely to wash out.  Pardon my drawing, but in the above picture I have drawn a red line as an example, where I think the new edge might be if we were to reduce the flashings.  

The final step would be to remove and replace the sand in the traps after the construction. While this is just a preliminary examination, we believe we have identified the issue.  Our next step will to be produce an action plan, discover costs and present our findings to the greens committee. 

In the mean time we are continuing to manually remove the rocks from the traps as they are raked, and collecting the silt after heavy rain falls.

Below is a picture of our rock collection to date, hand picked from traps as the staff rakes the traps.