Cobb's Creek Case Study 1: Drainage and Flooding

[Kyle Harris]

I took the opportunity to take a look at Cobb's Creek (the actual creek) after the significant rain we've received in the Philadelphia area lately. To anyone who has played the golf course, it is apparent that the course takes a beating from the creek in times of frequent rain. What better opportunity to identify and locate problem areas than after a rain storm?

First, here is an aerial overview showing some of the general flow of the ground. I've highlighted the flow pattern of the creek and drainage coming off the hillside in blue. The red lines show a very general "shape" of the hillside and the yellow boxes outline some of the trouble areas.



As is apparent, the area through which the 3rd, 4th and 5th holes are routed must take a series of concentrated surface water from the somewhat convoluted hillside to the north. Once one gets to the 7th hole, the hillside is a lot broader and less severe and as a result the creek is straighter and a bit wider.

Let's now take a look at the 3rd Green:





From the fairway, we see the creek enters the area from directly behind the green and then enters play from the viewers right. Some erosion is evident even from this vantage point 130 yards away.



The view back down the fairway shows evidence of the creek's height with major flooding. It is probably not coincidentally that the creek is overflowing the retaining wall at the point where it curves and begins a much straighter path toward Lansdowne Ave. in the distance. Fortunately, such damage is the extent of the erosion on this hole as the green is protected by a high retaining wall. Here's a view from the same spot looking upstream:



4th Hole in the next post.

[Kyle Harris]

Unique to Cobb's Creek (the golf course) is the walk through the woods alongside the eponymous water body from the 3rd green to the 4th tee. Incidentally, such a walk follows the creek upstream so it is helpful for this case study to work through the holes in order.

As is apparent from the aerial, the 4th hole area is near the confluence of a small tributary from the north that flows in front of the 17th green. The green is located on a peninsula just upstream from the meeting point and an island was created to provide the golfer a higher/drier drop area in the instance of plunking one in the creek.

Along the walk to the 4th tee, I spotted a potential bottleneck in the creek created by several large boulders.
Downstream view:


Upstream view:


Downstream from in front of 4th tee showing the narrowing due to the boulders:


Without paying too much attention while playing, I speculated from the aerial that the water flowed through the area in this fashion. The thickness of the lines showing relative amount of flow.



Much to my surprise, I found that the water actually takes the longer route around the island toward the 17th green/5th tee instead of the shorter/straighter route.



I further tested this by dropping leaves at various points upstream and seeing which path they took. Doing this 30 times, 24 took the longer route.

Furthermore, I was amazed by how little the tributary from the 17th actually carried.
View from in front of the 17th tee:


The area in front of 4 from the 5th tee:


The island:


The 17th hole tributary meeting the major portion of the creek:


The area directly in front of the green, showing the majority of the flow taking the longer route:


The downstream meeting on the tee side of the island, the boulders from the right side significantly slow down the flow on the direct route:


The right side (more direct) channel:

[Kyle Harris]

On no other point does the namesake creek enter into the golfer's mind than on the 5th tee.

The creek is practically the center line of the hole, with room right and left to hit a tee shot.

The intimidating view from the back tee:


Fortunately, the creek is both wide enough and unobstructed through much of the course of the hole, so the flood damage here is localized to specific areas.

Part of the reason is that the creek bed between the 4th green and the bridge to the left fairway is almost completely devoid of obstruction:


Looking upstream from the bridge, we see the creek is in fairly good condition and maintenance is limited to standard creek maintenance found on most other golf courses, the water was moving quickly and without obstruction in this portion:


At the rough midpoint of the hole, we find the retaining wall to have significant damage behind it, presumably from flooding overflow:


Looking downstream:


This seems to be a case of an extreme flood causing the start of erosion behind the retaining wall that went unchecked for years, and perhaps even decades. The current issues seems to be more with eddy currents eating away at the portion of the bank where the wall ends downstream and slowly filling with water. This was obviously a sensitive area to begin with, as the wall only bolsters this portion of the creek.

Further upstream is the cart path/dam/bridge:


Note how the dam acts as a bit of a flow control for the creek downstream.

A bit worrisome is this area behind the 5th green which is slowly being eroded by the bend in the creek:

[Kyle Harris]

The last portion of this analysis will look at a potential solution to major flooding issues down stream and centers on this portion next to the 6th green:



This area seems ideally suited for the construction of a small dam. Simply dredge out a portion of the land on the left side of the picture and build a wing dam.

Furthermore, this adds a rather nice water hazard to the hole that would form the left boundary of a restored "island" green. By the way, this is the green pictured in Geoff Shackelford's "Golden Age of Golf In America."

Here's the view from the green, looking downstream:

[Joel_Stewart]

Good post.  Seems like cleaning out the boulders and obstructions would help improve the water flow.  Of course I prefice this with the master plan being completed and the routing restored.

[Kyle Harris]

Joel,

As I was wandering about, I got to thinking just how one could implement a master plan. Should the original routing be restored, a significant amount of fill would be gained by the elimination of the current 16th tee. Why not use the fill to backfill the rebuilt retaining walls? Alongside the creek on 5, for example, would probably use about half the fill from that tee.

I think a full master plan would be a lot cheaper to execute than originally thought.

[Steve_ Shaffer]

Kyle,

It is my understanding that the 3rd green needs to be rebuilt from the ground up. If I remember correctly, Mark S told us this was the case.

[Jeff_Brauer]

I haven't studied the situation beyond Kyle's post, but I would guess with 99% certainty that the boulders in the stream are a mere pimple to the water flowing downstream.  The flooding doesn't come from the golf course side - it comes from urban areas (not urban when the course was built) from miles upstream, etc.

Adding ponds in the areas shown would probably be too small to signifigantly add retention.  Adding a dam, if it raised water level - would actually reduce it, causing more flooding.

An engineer would see what the flood levels are and probably raise greens and straighten the channel through the woods, causing great destruction of the natural beauty.  The only thing that will lessen flooding there will be a substantial increase in the cross sectional flow area of the channel CONSISTENTLY along its length, from where it flows out downstream right back to the golf course.  He would probably hard surface that channel, too, to make sure it doesn't erode away further.  Someone thought of that with the walls, but they are probably too small for current urban runoff.

It would be a tough choice for anyone, but probably better in the long term for the golf cousre to figure a way to corral that flooding.  

[Kyle Harris]

Kyle,

It is my understanding that the 3rd green needs to be rebuilt from the ground up. If I remember correctly, Mark S told us this was the case.

That would not surprise me one bit - it seems very sandy as is and I don't believe I've ever seen a picture of it in July where it looked remotely healthy.

I often wonder if simple aggressive cultivation practices and the introduction of some organics would help there. Aerate/topdress aggressively in March and April and see what happens.

[Steve_ Shaffer]

I don't think that will work given what Mark S said about the poor construction of the green. It was rebuilt recently and the contractor may have screwed up the mix.

[Kyle Harris]

I haven't studied the situation beyond Kyle's post, but I would guess with 99% certainty that the boulders in the stream are a mere pimple to the water flowing downstream.  The flooding doesn't come from the golf course side - it comes from urban areas (not urban when the course was built) from miles upstream, etc.

Adding ponds in the areas shown would probably be too small to signifigantly add retention.  Adding a dam, if it raised water level - would actually reduce it, causing more flooding.

An engineer would see what the flood levels are and probably raise greens and straighten the channel through the woods, causing great destruction of the natural beauty.  The only thing that will lessen flooding there will be a substantial increase in the cross sectional flow area of the channel CONSISTENTLY along its length, from where it flows out downstream right back to the golf course.  He would probably hard surface that channel, too, to make sure it doesn't erode away further.  Someone thought of that with the walls, but they are probably too small for current urban runoff.

It would be a tough choice for anyone, but probably better in the long term for the golf cousre to figure a way to corral that flooding.  

Jeff,

I was hoping someone with a lot more experience with this sort of things would chime in. In the areas that are less severe, the channel is actually fairly straight. While I don't doubt that the urbanization in the area has contributed to the flooding issue I also wonder just how much more urbanized that area is as compared to 1920 or so. Cobb's Creek is relatively close to the city. Upstream is Merion, downstream the 69th Street Terminal and ultimately the Tinicum/Heinz Wildlife preserve next to the Airport.

Obviously, before drawing any final conclusions I think one needs to catalogue the drainage after a summer rainstorm. The fairways and greens were as firm as any other golf course in the area during/right after significant rain.

I am curious how quickly it will dry out.

[Willie_Dow]

Thanks Kyle for your concern downstream.  We have to catch this condition upstream, somehow.  Catch basins are the answer, how we get them is the question.

[Kyle Harris]

Thanks Kyle for your concern downstream.  We have to catch this condition upstream, somehow.  Catch basins are the answer, how we get them is the question.

I see a large open plot of land along the creek where it crosses Ardmore Ave. Why not just dig a few there? 

Seriously though, does anybody know how frequently the creek actually over flows the retention walls? Are the greens ever under water?

As I mentioned, I was surprised at how dry the place was considering. Certainly not ready for carts, but not a swamp either.

[Willie_Dow]

Kyle:  Actually, the plot of land below Ardmore Ave. is a retemtion and sedimentation basin which accumulates tons of water around the llth green.  The culvert which takes that flow down Cobbs Creek is not large enough to relieve that dam.

[Mike_Cirba]

Hey Kyle,

Nice work.

Tell us about the location of the 13th tee.   I got a cryptic brief message on my voice mail from you...perhaps the overhead map might help.

Thanks!

[John Chilver-Stainer]

Has a hydrogeological engineer had any input on this? A small investment will give you the right answers rather than going through the guesswork.
 
The water speed along the channel is a function of the cross sectional area, the wetted area, longitudinal inclination and the coefficient of roughness of the channel surfaces.
Cleaning out the river bed, which appears to have sediment collection, is the first thing to do - this will improve the cross sectional area and the roughness factor.

Often records of previous floods indicate the expected high water marks and so the water quantities can be evaluated and the statistical frequency of different high water marks prognosed for 10 year, 25 year, 100 year or even 1000 years. Depending on the importance of the protected area the heights of the channel including a free-board can be defined.

On at least four of my golf courses the environmental authorities required that the golf course accept deliberate flooding to avoid flooding of more important areas and to act as a retention basin relieving the flow of water down stream. In such cases I design the greens and tees above the expected high water mark.

The damage to the wall has probably more to do with scouring and undermining of the wall the foundations than the overflow. It should be rebuilt with deeper foundations.

My experience with flooded golf courses are that there is often little if any erosion of well established grass surfaces. By far the worst problem is the removal of sediment, but is probably cheaper than construction a flood proof channel not to mention maintaining the landscape integrity of the golf course environment.

[Lyne Morrison]

'In such cases I design the greens and tees above the expected high water mark.'

John - are you able to elaborate further re your experience of which high water mark would be reasonably tolerable for usga greens
recoverability - 10, 25, 50 year?? (in the event of possible future, but infrequent flooding)

Obviously the higher the better and minimising flood impact is the ideal. I am in the planning stages of a project at the moment
where the 100 year level is high on the site but am keen to minimise the impact of fill for greens and tees.

Thanks for any additional feedback you can offer.

Cheers -- Lyne

[Lyne Morrison]

I should add that comments from others are welcome..   

Cheers -- L

[Jeff_Brauer]

Lyne,

As you say, 100 year flood is preferred, and I have set them there only to get a CYA letter from the Contractor telling the owner it should be 1.5-2' above 100 year flood to account for wave action and/or keep the entire USGA substructure from flooding, which I agree is ideal.

I have built several courses with greens as low as 50 year flood level, because the fill requirements were just impossible to get much higher, and also reasoning that now that the USGA admits there is an expected life cycle to the greens of about 15-25 years, its 4 times more likely that the green will be rebuilt voluntarily over a forced rebuilding due to flood.

John,

I have minimized flood damage on golf courses by building a small lip on the creek bank and only allowing flood waters to "back in" to the golf course, which reduces flow velocity while keeping the same flood volumes.  I agree that a civil engineer is best qualified for major flood work, as long as they leave the aesthetics to a gca!

[Lyne Morrison]

Jeff - thanks for your perspective as my feeling is the 100 yr level is unrealistic for a portion of this site.

By the way we met many years ago - at a conference in Queensland if my recall is right - I appreciate your input to this site.

Cheers  -- Lyne

[John Chilver-Stainer]

Lyne

I usually design to the high water mark stipulated for the channel by the authorities.

The high water mark is usually calculated only for the water flow in the channel itself, not outside of it. Once the water overflows there is a much larger area for the water to disperse and so another calculation should be made, or as I do just assume the water will not rise much further and take the height of the channel plus a freeboard of 25cm or so.
As Jeff says the normal life of a green is assumed to be 25 years and is often shorter so overdesigning the height of the green is a bit pointless.

To conclude, the playability of the green should have priority over the flood protection issues, as the removal of sediment from the green surface is not necesarily a high cost. The bunker repairs will cause you more headaches!!

[Lyne Morrison]

John - thanks for your input, that's great. We've had drought conditions here for so long that it is hard to imagine this particular creek
coming back to life but as we say - it will rain again -- one day, so worth checking these boxes.

Cheers, Lyne

[Jeff_Brauer]

Jeff - thanks for your perspective as my feeling is the 100 yr level is unrealistic for a portion of this site.

By the way we met many years ago - at a conference in Queensland if my recall is right - I appreciate your input to this site.

Cheers  -- Lyne

I should add that I have considered going as low as 25 year protection when filling to higher levels was impractical.  I know of some floodplain courses where they are flat and every green is in the air 8-10 feet, making it unplayable for 99 years to make the one year allow for a slightly faster recovery.

Lyne,

I did give a speech in Brisbane about 1993, sharing the stage with a most gracious David Graham, who also lived in Dallas at the time.  I think his opening remarks were something to the effect that we had to stop meeting this way!  I also presented at the  Club Managers meeting in Sydney in Novemeber 1994, which remains one of the highlights of my life (the conference and trip, not my speech!)