Plumbing on a much larger scale...
So, you say you want to do this pond thing right and install a drain. Very well, forget about your pipe wrenches and multiple trips to the hardware store. You are about to embark on a slightly higher level of "drain-ocity".
Let's start with the actual drain line. We settled on 6" PVC pressure quality pipe...of course, it runs thru the base of the dam. Hmmm....we better install it first, eh?
John sets up his laser level on the tripod at the very end of drain run, at the outlet. This is one 'spensive, hi tech laser level. It not only projects a rotating laser beam that can be picked up anywhere within 2000 ft at line-of-sight, but it can also be programmed for elevation changes. It's cost is upwards of $10,000 (...nice to know that our money is well spent). We already know where the dam is going to be located. We know the final height of the dam and the slope on the water side. This will dictate the location of the intake end of the drain. We know the existing grade elevation at the outlet end (located at the tripod in pic above). All this info allows us to calculate the length of the drain, which turns out to be over 300 ft long. It also allows us put an ever-so-slight positive down-hill trajectory on the pipe so water will run in the right direction, away from the pond. Because we want the inlet side of the drain to be as low as possible within the pond, John puts a 4" elevation change over the 300+ ft run....that's right, 4 inches. I'm thinking that he's nuts. Heck, he's gonna have 12" dips in the drain trench just from the inaccuracy of digging with that big ol' backhoe! Wrong-oh, non-believer.
Here's what happens. My job is to use the measuring rod with the laser beeper attached to the top (pic above). When the laser beam hits the receiving unit attached to the top, an audible alarm "beeps". When it is dead-nuts right on the money, it is a constant tone. Now, the really cool part. This laser is programmed and aimed to shoot the beam in an uphill trajectory so that the beam is 4" higher at the other end of the pipe based on all our measurements. So, as we move along the length of the pipe trench, the depth is constantly being adjusted to move uphill to create a 4" elevation rise as we work toward the inlet end, some 300+ feet away.
OK, assuming that the author can accurately place the measuring rod within the base of the trench...and that he can discern between a beep and a constant tone, the accuracy of this entire project now rests with the guy digging the trench. Well, let me put it this way. If you could attach a pen to the bucket of that backhoe, John could sign his name on a sheet of notebook paper with it. I worked with him, foot by foot, measuring all the way. When I needed an inch removed, he took off an inch. If he went a little too deep (and that wasn't very often...and never more than a couple of inches), he would carefully kick back a few clay crumbs and pack it with the flat bottom of the bucket. Amazing control and accuracy. This is just one more reason why I am not attempting this stuff as "do-it-yourself".
Yes, thank goodness that there is some flexibility over the length...not much, but enough for directional compensation.
There are 2 anti-seep collars placed with the run. These are used to ensure that there is no seepage of water along the length of the pipe after the pond fills. In essence, they are 1/4" thick PVC plate x 48" square that are sealed and attached to a 6" PVC fitting running thru the exact center of the plate. The theory is simple. If a trickle of water begins it's journey from the pond, it will likely follow this drain pipe all the way to the other end. If we interrupt this trickle and force it away from the pipe by 24", it has to make a 180 degree turn at the edge of the anti-seep collar, follow it 24" back AND find the drain pipe again to continue. 2 of these collars are recommended as best practice.
John calls 'em "crumbs"....the finer particles of clay that pack the best. When he is excavating a project where they will be valuable for well-packed fill, he is able to segregate them for re-use later. He then uses the teeth on the bucket to sift thru a pile, like running your fingers through clumped sugar. John drops in crumbs around the collar and then we hand-tamp them into place.
There are a few different designs of anti-seep collars. In my humble opinion, they all pale by comparison to this PVC design by Easyway Plastics Co. My pond contractor, who has dozens of pond constructions in his resume', totally agrees. The plastic sheet is stout and stays in place while dropping buckets of dirt around it. The simple design of using a customized PVC coupling and flange for connection to the pipe is the final word on strong, easy to install, and functional. Yes, they cost a little more than those other flimsy, cheesey collars made outta rubber, but this is a critical facet to holding back pond water within a dam. Once this thing is buried beneath 15 or 20 feet of earthen dam, there really is no second chance...so you better get it right the first time. Don't pull up short.
Finally...all 300+ feet of drain is installed. Oh yeah, and the valve is in there too. It will be left unburied until the bitter end of pond construction. Then, close her up, protect her with a short pc of vertical culvert pipe with a cap, document the location, and bury her in a whole buncha dirt. Hopefully it is never needed or gets used. If it is needed, though, some diggin' will be worth the blessing of it's operation.
...almost done with this long pipe...almost. The last part of the job is also critical. It is the proper compaction of the clay soil around the length of this pipe. Yes, the anti-seep collars will help to thwart unwanted water following the pipe's length, but their purpose is secondary. The primary seep retardant is a firm, compacted seal of the clay soil against the exterior of the pipe. John and I discuss it one night last Spring when he mentions that he just bought a compactor that we can use. This is a generous and wise offer. I volunteer the duty of execution. I had used a vibratory plate compactor before. They are heavy to set into place, but pretty easy to operate and follow as they vibrate and compact the soil into place. When the day comes, I am introduced to another type of compactor....one I never suspected, tho I know that I had seen it somewhere before.
Have you ever wrestled with a kangaroo on steroids? Have you ever done it for 2-1/2 hours straight in 93 degrees? This thing is a nitro-powered jumping jack and man, does it work! It strokes up and down vertically at a bone-jarring pace. I estimate the clay soil would compact 4" - 5" after a couple of seconds of pounding. Oyyy...get me the Motrin 800!
OK, Mr Mega-plumber...is that it?
Nope, not quite. Even your bathtub drain normally has some kind of flow obstruction to catch junk before it heads south and potentially clogs. This one is no different. Because we have installed a butterfly valve, there is a vane within the valve body that can potentially catch debris (the story at the end of this page will demonstrate this potential catastrophe). The answer, then, is a filter unit at the intake.
This piece is a strainer pipe. It is a 5 ft section of the same 6" PVC pipe with 24 rows of holes, 12 holes per row....total 288 of 'em that are .750" in diameter. It is glued onto a 90 degree elbow, attached to the end of the drain pipe at the base of the dam.
Oh, and by the way, about 80% of the dam has now been put into place.
Whoa!... we ain't done with the drain, yet. The strainer is now in place (the vertical white pipe at the base of the dam mass in above pic). The final part is the filter case.
I started with a trip to the nursery/garden supply. We needed hard, jagged rock that will lock itself into place; smooth river rock won't git it No, no limestone or driveway gravel either. Limestone will soften over years of exposure to moisture. I found a perfect match and bought 800# in bulk ($39). The holes on the strainer pipe and the filter case are 3/4" dia. I don't want any rocks falling in thru the strainer pipe and possibly lodging at the butterfly valve, so I had to screed the stock:
The screen is chicken wire; it worked perfect and left me the bigger, jagged chunks.
Then, get a 7 - 8 ft section of 15" dual wall, smooth core perforated culvert pipe. Dual wall is a must for rigidity and stability. The factory perf. holes ain't gonna deliver, so give 'em some help...and add a whole bunch more:
Then cut a saddle out of one end to slip over the horizontal portion of the 6" PVC drain:
...pound in a couple of T-bars to stabilize the filter, centering the strainer pipe within...copper 12 ga electical wire and twist with a bar to tighten. I added 2 more opposing T-bars to encompass the entire assembly:
OK, time for the stone...one bucket at a time, up and over taking care to make sure the stones surround the strainer pipe in equal thickness, ensuring it is centralized and the assembly remains vertical. A peek in from the top before the top of the strainer disappears:
...then, one more bucketful and we're done:
The idea here is that we have created a self-cleaning drain filter. First, there are 288 .750" dia holes in the strainer pipe and over 300 holes of same in the filter case. This will distribute the suction well, minimizing extremes. Having the holes at the valley of the ribs on the filter case also keeps debris at bay. In the event leaves or debris begin to cling to the filter case, close the valve, eliminate the suction, wait awhile and hopefully they fall away. One thing for certain, no debris will get into the drain pipe and hang up on the valve vane. Oh yeah, I did NOT glue the top cap on the 6" PVC strainer pipe. I sanded out the mating surface of the PVC cap so that it slid on and off easily, they put a couple of stainless steel screws in from the side. If the pipe gets clogged for any reason, I have another cool invention that can go in from the top to blow 'er out...
Jeesh, what the heck is that thing?
...another invention off of the "UH-OH, gotta bail my butt out again" drawing board.
So, when we completed installation of the 6" PVC drain with nothing more than open pipes at both ends and a valve somewhere in between, the dam construction began. I had the presence of mind to open the valve during this time...very estute, eh? Well, of course it rained...and the pipe ran great. OK, a couple days later....the dam is about 80% done and Donna and I return to the site to install the vertical PVC Strainer pipe on the drain inlet at the pond side of the dam.
All goes well, we go home, and it pours that night. The next day, there is 3 - 4 feet of water surrounding the strainer pipe, covering about 1/3 of the holes...THE WATER AIN'T GOIN' DOWN!
There is barely a trickle of water coming out of the drain outlet at the other end. The valve is wide open! John, my contractor, and I are queasy with thoughts of the worst case scenario. How can this be? It ran fine 3 days ago. Did the pipe collapse...nah. Is the exterior of the strainer pipe clogged with leaves? It was about 7 feet from the mini-pond shore...a couple of splashes and scrapes with a 2 x 4 reveal the holes are open and clear. I go to the valve and slowly spin it closed, then open a couple of times. It works fine, yet no change in the flow...still only a trickle out the downstream exit. There must be a clog. The pipe is over 300 feet long, there is 15 feet of dam over it, and we gotta unclog it. I ask John if he has a trash pump...Yes, a 3" unit. We gotta try blowing the pipe out. He only has enough hose to draw from the mini-pond and flush from the strainer end...no way can we consider blowing from the down-stream exit end. Well, I did one smart thing with the strainer...the cap is not glued on top...it's held with SS screws. So, how are we gonna get past 288 holes on the strainer pipe? We have to get the trash pump output hose to solid 6" PVC, somewhere just below the water, or the pressure is gonna just blow water outta the strainer pipe holes. As I'm driving home, my little brain is smokin'. Here is what I got:
It's 6 ft of 3" PVC pipe with a 90 degree fitting at the top and a 3" fitting to attach to the trash pump output hose. The other end is pure luck. I had about 3 different plans in my head for this end...plan #2 worked. I found a rubber connector for PVC-Clay. Remove the big hose clamp from the clay end and it just fits inside a 6" PVC pipe I.D.....unbelieveable. It's like a rubber piston.
John parks the track hoe next to the mini-pond, I climb into the bucket, and he hovers me over the water, right next to the partially sumbmerged strainer pipe. I pop the cap off, insert the piston until it hits the 90 degree elbow just below. We hook up the trash pump output hose and John fires it up. I'm a pretty big guy, and the pressure when the pump is idle-slow is pushin' out the drainbuster and pickin' me up outta the bucket. A few tries with the Brettski drainbuster, a couple of twists of the valve back and forth....whooosh! Leaves, tiny sticks, black gunk, and a big ball of frogs.
QUICK...get the filter case onto that strainer!!!
So...the moral of the story: If there is going to be any obstruction within the your drain pipe (like the vane of a butterfly valve), you better seriously consider filtering the inlet end. Oh yeah, and do it before the first rain.