Diversion syphons can divert water around erosion control structures during their construction in small streams or creeks on farmland. Syphons made with 90mm PVC stormwater pipe for high flow and syphons of flexible garden hose for low flow are discussed.
Both the large and small syphons can have some simple DIY additions that can greatly improve the syphon’s stability, pumping performance and utility. For the large syphons, the modification of the syphon’s entry will even allow it to excavate and transport gravel and small rocks.
Similarly, for the smaller hose syphons, the additions can automatically regulate the outlet flow rate in balance with the inflow rate. Consequently, within reasonable flow limits, flooding of the worksite can be automatically prevented while the site is in use or unattended.
The video below may provide a better context about how my newest (in construction) erosion control structures link to an old one
Finally, a water tube surveying level can be made as a syphon to make it ‘spill-free’ and easy to use with one operator to mark benchmark levels within and between worksites.
Introduction and background to the use of water diversion syphons during the construction of erosion control devices in farm streams
For many years on my farm, I have tinkered with constructing many erosion control/repair devices in streams with deep gully erosion. The devices are usually built with rocks, waste concrete and sometimes baked clay bricks and manufactured concrete blocks. Invariably, the components are held in place with mortar made from Portland cement mixed with either sharp-washed sand or local stream gravel and alluvial silt.
The erosion control structures consist of an essential base or flat bed of concrete that can dissipate the energy of falling water. On the upstream end of the base, a wall is constructed to raise the water level on the upstream side. This forms a waterfall in the water course.
Upstream of the structure, the water level rises and slows the water velocity within the terrace. This promotes the deposition of stream alluvium during flooding. The alluvium and water can also support aquatic plants. Such plants can actively recruit fine particles from the water. As the flood terrace above the wall grows and fills with alluvium, the wall can be made higher to further lift the water level and the stream bed. The concrete base in the structure can dissipate the kinetic energy of the falling water. Eventually, the erosion gully can be filled and the terrace flooding zone can reach the base of the next upstream control structure if positioned optimally.
“The strength of the base is critical to success. If the wall or ‘beaver dam’ is formed, it may hold back water and build up silt for some time. However, without a high-impact resistant base for the waterfall to safely dissipate its energy on, a big hole will eventually form and all the collected alluvium will be lost and the erosion will be even greater.”
A series of such structures can, with time, fill the erosion gullies with alluvium that will become stabilized with water-tolerant vegetation and roots from adjacent trees. In this way, the ugly gully erosion scars, often with exposed lifeless subsoil, are healed and the beautiful original alluvial valley can, with help, be restored by nature.
The constructed wall can have short lengths of 90mm PVC stormwater pipes cemented into them to form temporary water bypasses while extending the wall or doing base maintenance. It also can be used as a convenient self-priming input to a large syphon pipe that can even bypass a downstream construction site.
Such wall pipes can also be capped when the site work is finished. However, while the initial base and the first section of the wall are being constructed, the base stream flow* must be intercepted and bypassed around the worksite to allow effective concrete placement and construction using cement mortars.
Note* In my experience, there has always been a small water flow at most worksites, even during the worst extended summer drought when the stream superficially looks ‘bone dry’. It is often invisible and flows through the gravel within the stream bed. By deep interception of these flows in a suitable hollow, a syphon can be used to bypass the work site. If the well is suitably wide and deep, it can also act as an onsite source of water to make the cement mortars used in construction.
Note about photos. I have prepared this post during a long dry period and have been unable to include images and sounds of cascading waterfalls and even rock fountains gushing from pipes, These will have to wait until Mother Nature sends her inevitable heavy rains.
Theories about water syphons and definitions
Water syphons use air-tight pipes or tubes to convey fluids down a gradient using the differential pressure between the water exit and the entry.
After so many years of ignorance, I was quite surprised to find that the differential air pressure model or theory of syphons was not the only one. Other valid theories include differential gravitational pull in water columns of different lengths and chain theory. According to the above reference, the differential air pressure theory is debunked by experiments that showed syphons could work in a vacuum. So there are multiple valid theories about how syphons work.
Regardless of the syphon theories, syphons make simple tools to divert water flows. Another more practical article on siphons to lower water tables gives a good technical description of a basic syphon. It also discusses appropriate pipe diameters to match particular flow rates when syphoning saline groundwater from bores to lower the water table.
Is it a syphon if it has no lift? It appears, by the above definitions and descriptions, that a syphon must have a fluid lifting path from the reservoir before the fluid flows down to the exit at a lower level than the surface of the source reservoir. Some of the devices that I describe in this post do not have this lifting element or sometimes change between non-lifting and lifting. However, they behave much like a syphon and their performance can equally be augmented by my tricky entry and exit devices that I use on ‘real syphons’. So, while not technically correct, I will continue to call all the devices syphons as I have no other suitable name for some of them.
“Luckily, these ‘non-lifting syphons’ are very practical, easy to start without a requirement for formal priming and usually, they cope well with less than optimal entry and exit management. “At worst, they perform like a covered aqueduct.” With appropriate entry and exit augmentation, they can suck so strongly that they can lower the level of the incoming water source so that very significant water lifting happens and by definition, they become true syphons.
They can even suck so strongly that they can transport small rocks (less than 90mm) and gravel with the water in a fluidized mixture that can have less than 50% water in the mix! “So I consider that ‘syphon’ is an appropriate name for my devices even though they may not always have a lifting phase and they may carry solids.”
Required flow rate and syphon pipe diameter. In the reference above about groundwater syphons, they tabulate appropriate pipe diameters etc to match the expected flow rate. I have only ever needed to use syphons made of flexible hose (12-45mm ID) for low-flow situations and rigid 90mm storm water pipe for high-flow situations.
Sometimes I use them in combination and also with multiple 90mm syphons to provide adequate bypassing with high stream flow. Similarly mature upstream structures can be used as pickup points for powerful bypass syphons that may bypass one or more downstream work sites while stream flows are quite strong. Such long bypass pip
The following series of photos show an example a series of linked erosion control structures that span about 15m of stream bed where it drops about 3m over this distance,
Syphon entry and exit augmentation. For the large diameter syphons, I have learned to carefully modify and manage the siphon inlet and outlet to enhance flow rate and allow the transport of rocks and gravel when required. The modifications are mainly made with short lengths of storm-water pipe and a variety of press-on pipe fittings that are versatile, abundantly available, and cheap. Most of these PVC components are just pressed together without glue so that they can be adjusted and reconfigured for future uses.
Similarly, for the hose syphon, simple modifications to the inlet and outlet can make the syphon automatically and robustly maintain a suitably low worksite water level without ‘breaking the syphon’s vacuum. The syphon can stall and then start again without any intervention or need to re-prime the hose with water. The inlet and outlet modifications will be described in detail later with examples of each syphon variant.
Depending upon the work site and the stage of the development of my erosion control structure and the stream flow rate, I usually use two or more of the various siphons described in this post.
Features shown are: The high-impact concrete base to absorb the energy of the waterfall, concrete block walls on either side to contain the flood flow, a weeping well and concrete plug(to the left of the green crate), a drainage sump (five-sided), further away, there is another drainage sump (four-sided) that is connected to the first sump by a 90mm PVC pipe and it connects to another pipe below the base that drains the water away to bypass the work site structures, a beam across the base (in front of the ladder) that will help to form a long water pool for the waterfall, from the culvert, to splash into during normal stream flows. Lastly, Just beyond the last white bucket, is the lip of the last waterfall that drops down to the level of the stream bed via another high-impact concrete base with walls.
I describe the hose syphons first as they are the ones that I preferably use when starting to build the base of an erosion control structure under low flow conditions during summer. When the base is completed, I construct a dwarf wall and put a short length of 90mm PVC pipe through the wall and cement it in place. When this pipe is connected to a suitable syphon, it allows the continued work on the site even if there is a significant stream flow,
Such short pipes can easily be blanked off when not in use or no longer required. “Mother Nature will eventually block it off anyway in my experience and the particles seem to lock in place like very poor concrete.” The pipe also can have a riser added, upstream of the wall, via an elbow fitting. This means that the pipe can still be used when it would otherwise become covered with alluvium. Additional pipes can also be added to the wall as it is built up and is steadily filled with alluvium.
Hose for low-flow water diversion syphons
Water filtration for hose syphons. For low-flow water diversions, crude filtration helps to prevent the blocking of the syphon. I started by making a filter extension for the hose. Made of heavy steel pipe with many slots cut into it. This device would sink in a puddle and water could be siphoned out. However, the horizontal orientation easily allowed the syphon to ‘sip air and fail’ when the water level was low or disturbed. I found that a weeping-well described next was a better alternative.
A weeping-well with filtration to feed a water diversion syphons. With very low stream flows, I find that a voluminous and deep weeping-well makes a very effective water collection point for the start of the diversion syphon. The volume of the well buffers small changes between the inflow and outflow rates so that the syphon can be kept air-free (or air-locked). The well depth makes it easy to start the syphon and hold the siphon hose tip well below the water surface. Lastly, it makes a very practical water source for making concrete and mortar.
Critically, the depth of the will determine the maximum pressure head that can be developed between the inlet and outlet without risking air leakage into the syphon at the entry. As in the above sketch, half of the depth of the well can be used to safely drive the pressure differential while the other half can be used as the air-lock. The depth also makes the system tolerant to small errors while setting the level of the rim of the exit pot as discussed later.
The weeping-well can be made of a large waste plastic container. I make the wells from scraps of 250mm diameter PVC pipe. They can have many slots cut in them with an angle grinder and a simple concrete bottom can be formed in them before deployment. When the well is sunken into a low point in a gravel bed it collects filtered water from the work site to feed the syphon either through the slots or if needed over the top rim.
Usually. I surround the wells with small pebbles and rocks that will not fit through the slots in the well. The well can then be held in place with a collar of cement mortar around the top rim of the well. Lastly, I make a bung for the weeping-well to keep it free of alluvium while not in use.
The bung is made from a suitable plastic flower pot filled with concrete. I sit the pot in the well opening while the concrete cures to ensure a good fit.
A pot for outlets of hose water diversion syphons. Initially, I used a natural downstream puddle as an airlock for the exit point for the diversion syphon. Unfortunately, such puddles are seldom in the best place for ideal syphon performance and they can flood or dry up.
Consequently, I now use a movable pot, such as a tall Fowlers preserving jar instead of a puddle. It can be dug into the stream bed so that the rim height is precisely set at the same level as the lowest drainage water level allowed in the weeping-well. This provides an airlock for each end of the syphon. It also means that when the syphon drains the well to its critical low level, the diversion syphon will stop. Then as the well fills the syphon will flow faster commensurate with the inflow rate. In this way, the syphon can automatically maintain a suitably low and steady water level at the worksite to keep the workings dry, even when unattended while cement is setting/curing.
The finishing touch to for hose water diversion syphons. The exit end of the syphon can be better directed into the pot and it can form a more secure airlock if it can have a downward pointing direction. An elbow with one branch blocked off and short piece of hose on the other branch can achieve this.
After recovering from many wasp stings when ambushed by many angry European Wasps I was ready to boast about the automatic syphon working for many days without my attention. However, I did notice that the flow rate had slowed and the weeping well was flooded by about 15cm of water. Eventually, I found that the sharp edges of the internal T-piece had been catching small sticks and fibres that were slowly blocking the diversion syphon. I should have anticipated this as such ”micro Beaver Dams’ periodically block my farm water supply pipe.
To correct the blockage problem I made an elbow without any ‘catch points’ inside. This elbow was made from 20mm OD PVC conduit. It was initially glued together with solvent-based PVC plumbing glue. To make it stronger I added more glue to the outside of the joint and wrapped it several times with a stretched ribbon of pantyhose fabric while working the glue through all the layers. “In many of my posts, pantyhose is versatile DIY reinforcing fabric that will work with many glues PVA, contact adhesives, RTV silicone rubber, solvent craft glues and others.”
Lastly, I used a slice of inner tube from a skinny bicycle tyre to connect the elbow to the syphon hose, without creating internal catch points.
Starting the hose diversion syphon. With the weeping well and exit pot in place, the syphon can be primed by filling the hose with water. Then with the exit end blocked with a finger or rubber stopper or tap, the input end can be quickly put down deep into the well and the exit end can be quickly put into the exit pot and the stopper removed when the tip is submerged.
Sometimes, after such a start, the syphon flow is a little slow and I don’t quite know why. I suspect that little air or gas bubbles may get trapped between humps and hollows along the path of the soft syphon hose. Anyway, I find that the slow flow problem can be resolved by carefully lifting the hose near the well to form a hump. Then I steadily move the hump in the hose toward the exit. I think this action clears out any residual bubbles from the hose.
High-flow water diversion syphons made fom 90 mm PVC stormwater pipes and fittings
For high-flow water diversion syphons, I usually put a short piece of 90mm PVC pipe through the wall of the erosion control structure. With care, such pipes can be cemented in place even during significant stream flows.
To do this the wall can be provided with a bypass notch that keeps the water level below the pipe. Fast-setting cement or concrete helps the speed of the operation. When there’s an adequate set of the cement, the bypass notch can be quickly filled using fast-setting cement (or a DIY fast-setting agent such as alkaline sodium silicate) and the water can flow through the pipe.
Facing the fresh cement works on the upstream side with a flexible film of plastic (now extinct supermarket bag or clingwrap) also can help to bring the cement into water-resistant service quickly while the cement transforms to a set state and then to a stronger chemically cured state. “Ironically, excess water on fresh cement works improves the cure of cement.”
Accumulated alluvium will bury the original bypass pipe. However, it can still be accessed by fitting an elbow and riser tube to it. This means that a shorter riser can be attached when it is required to bypass water again and a longer one can be attached or it can be capped when it is idle.
Is it an aqueduct or a syphon or a siphon? Once the cement around the pipe has become adequately strong (2-3 d), the pipe can be gently connected to a long sloping length of 90mm storm water pipe to form a water diversion syphon. In this simple state, it will effectively transport water, but will not reach its highest possible performance as it will act more like an aqueduct than a syphon. Several cheap changes made at the entry and exit of the syphon pipe can allow it to reach its full theoretical flow rate and even more.
The need for a siphon exit airlock. The ‘straight-out’ exit of the above simple syphon will likely leak air inwards through the exit. This air can creep backwards up and over the downward-flowing water. “This means that it becomes a covered aqueduct.” A carefully placed hand, brick or rock, spaced at half a pipe diameter from the exit can bank up the water and prevent air entry. It also improves the flow rate. However, it will also restrict the full potential flow rate.
Siphon exit riser airlock. I learned that a simple and self-maintaining airlock can be made from a short riser pipe fitted into a cheap PVC elbow on the water diversion syphons exit. Putting it on the exit with the riser pointing upwards makes a perfect airlock. It causes minimal flow restriction with either 45 or 90-degree elbows and the water exits as a gentle fountain and air can not get back in regardless of the flow rate.
[Add a video of the syphon exit water fountain]
The increased water flow rate that is stimulated by the exit elbow and riser will, under high flow conditions, cause the entry end of the syphon to suck air. The vigour of the flow into the horizontal pipe entry will cause a water/air vortex and make loud slurping sounds “like Gulliver’s Brobdingnagian Giant sipping the remnants of a milkshake”.
After using many anti-cavitation devices such as plates, boards and metal sheets, I have settled on using yet another elbow with a tube fitted in it. When fitted to the entry of the diversion syphon, with a dropper tube pointing downwards, it will initially prevent cavitation by preventing the vortex from reaching the syphon inlet.
Are diversion syphon embellishments a success or failure? The combined success of the entry dropper and the exit riser will greatly increase the syphon’s flow rate. However, with most good ideas comes,,,,,……. you guessed it, a new problem of the incoming water level becoming so low that cavitation starts again. “As the old saying goes…..Success will often have many wantobe fathers, but failure will always be a bastard. Nevertheless, there are still cheap options to crack this vortex problem and even to exploit it to improve the flow rate of water diversion syphons.
Syphon entry vortex buster. The above vortex can be busted by simply lengthening the dropper pipe, so that the vortex can’t easily reach down to the syphon entry. This may require a water depth that is not available and sucking in rocks and alluvium may start a mining operation (more on that later).
As an alternative, a squat vortex buster can be made by putting a PVC T-piece onto the end of the dropper. This provides two entry points with smaller and shallower vortices.
The above vortex buster may not be strong enough, particularly when using a long syphon run with a large height differential. In this case, side pipes with multiple side-holes cut in them can be inserted into the above T-piece. This will break the two vortices into many more but weaker vortices and minimise cavitation or ‘sucking air’.
Syphon entry bell vortex eater for water diversion syphons On a very still night, I was in bed and listening to the distant periodic slurping sound coming from some of my creek syphons. While going off to sleep, it dawned on me that these were vacuum pumps hard at work. Perhaps these pumps could lift water high above the siphon entry so that the vortex could seldom reach down to the syphon entry?
I implemented this idea on a diversion syphon entry by rotating the very short entry dropper upwards to become a riser. The riser was made shallow enough to allow natural flooding and priming of the syphon. Then, over the riser, I placed a bell made from an inverted 20-litre oil drum, with the top removed. For a start, there was the normal slurping but it was muffled by the bell. Progressively, the sound intensity and frequency diminished. I could sense, by the weight of the bell, that it was slowly filling with water with each slurp and the flow through the syphon was getting stronger.
The bell collapsed a little but held its shape OK. Later I put some pieces of concrete on the soft stream bed for the bell to sit on. This prevented the bell from slowly sucking down into the alluvium. I also put a short steel stake into the stream bed to go inside the bell and prevent it from moving off its support base during flooding. The device worked exceptionally well and there were only small and infrequent muffled slurps inside the bell or on the outside of the bell if the water level in the stream got too low. In all situations, these water diversion syphons were self-priming and self-correcting.
With such a breakthrough it was tempting to think I had beaten the laws of nature or syphon theory. However, if we go back to the above siphon theory, we can see the improved water head height within the bell is neutralised completely by the lower air pressure in the bell that lifts the water in the bell.
“In the real world, you can improve something to get closer to theoretical perfection, but you don’t get nuffin for nuffin. But….but the mass flow rate in the next syphon may exceed the maximum theoretical flow for water.”
A rock and gravel slurping water diversion syphons. Big floods often dump alluvium in places where it is not wanted. As an example, I have a fence that has been buried to the top of the posts with such alluvium, and the replacement fence is at risk of the same outcome. At the same time, the floods can scour out holes where they are also not wanted. Consequently, transferring the excess alluvium to such holes can simultaneously solve two problems.
Quite by accident, I was siphoning water from a portion of a stream that had accumulated excessive alluvium along a fence line. The syphon had an elbow airlock on both ends of an 18 m-long diversion syphon tube. The inlet had a downward-pointing dropper on it. The suction was so great that it drained the pool in the stream bed. It started to slurp a mixture of water, air, rock and gravel. This mixture formed a fountain at the exit. The largest rocks lodged around the exit riser. Smaller rock spread a little further and progressively smaller alluvium particles moved on for some meters down the stream bed.
Using straight PVC joiners I added pipe extensions to the dropper. This allowed the diversion siphon to dig deeper. Eventually, the hole became a big crater that I stood in and the surrounding alluvium flowed in with water into the bottom of it. Large rocks that were too big for the pipe could be seen and intercepted as they tumbled down the crate slope. Digging or raking around the hole supplied the syphon pump with more alluvium (as a substitute for water). Eventually, the syphon was sucking up a rich mixture that was composed more of alluvium than water.
[Add a video of a stream bed crater being mined by a water diversion syphon.]
The mix makes a gentle tinkling sound as it moves down the diversion syphon pipe to the volcano at the exit. Now and then, large round rocks can be slurped up and these will rumble down the siphon. They act like a plunger, and clear air from the tube, making the flow rate even faster.
This makes an efficient way of transporting alluvium. I suspect that alluvial gold miners of old would have used similar devices to vacuum up and transport precious gold-bearing silt to sluice devices on an industrial scale. As part of the Hume and Hovell trail, I walked for more than two days on alongside streams that were sculptured by gold extraction. All the large rocks were removed and systematically stacked on the banks and beyond. They formed tracks, embankments and platforms, presumably for pay-dirt processing, camps and sly-grog shanties.
I find that it is interesting to consider that an alluvium diversion syphon can run at full capacity with less water input than is theoretically required. Rocks and gravel with a density of 2.6 kg/L can make up the volume. So, when the syphon carries 50% mixture of water/alluvium, the mass transfer rate will be about 1.8 times greater than the maximum flow with water alone.
[Add a video of a water alluvium fountain]
Safety Note: Suction forces at the diversion syphon’s entry can be immense and dangerously strong. It can grab a gumboot shovel or any flat object or rock that is too big to fit inside the syphon. It should be handled with great care. Consider a siphon made with three 6m lengths of 90mm PVC pipe. It would have an estimated 1,000 litre or kg of water in it at full power. This would increase to 1,800kg with a 50% alluvium mixture. Stopping this amount of water when moving quickly down a pipe will create a massive water hammer force. Usually, the pipe will collapse and fly apart in case of sudden blockage.
[Add a photo of a shattered pipe]]
” When syphoning water in such a syphon made with some unusual freshly made pipe that was ‘a little softish’ (possibly the plasticiser was overdone), the pipe collapsed as flat as an empty toothpaste tube when a tortoise shell came out of the alluvium and slapped onto the entry. Only the overlapping union areas survived as round shapes.”
It is a useful precaution to put a piece of very aged and brittle pipe into the head of the diversion syphon. This will be a sacrificial pipe that can collapse to protect the remainder of the pipes or an unfortunate body part that may get sucked in.
[Add a photo of a collapsed section of brittle pipe,]
Lastly, when we consider the dynamics of these powerful diversion syphons, when carrying alluvium, it is easier to accept the differential mass theory of syphons, rather than the air pressure one, as described in the introduction.
Using a syphon for surveying levels in a stream bed
Forever, I have used a water-filled 25m length of flexible and clear laboratory tube to mark levels on my construction sites. It is also great for planning the optimum locations of erosion control structures along my streams.
From experience, the tube is best stored dry as water left in it will grow algae and slime on the inside of the tube. This obscures the viewing of the water/air meniscus. Consequently filling the tube each time it is used is tedious and tricky to do without air bubbles getting into the tube and spoiling the accuracy of the level.
The tube can become a self-filling syphon by connecting it low down in a suitable large reservoir such as a large soft-drink or juice bottle. The tube can be filled quickly and easily from the bottle without entrapped air bubbles. Matching water level datum lines can be marked on the bottle and the tube while the tube and bottle are held side by side.
Then the tube can be taken to mark levels as a one-person operation up to 25m away from the reference datum mark. My only regret is that I did not learn this single-handed leveling trick with the bottle many years earlier.
Now it is some time since I have had an ode to share, so this one bubbled up around the wonderful sounding word syphon that I only recently discovered has two legitimate spellings;
Is a gravitational water transport device spelt syphon?
Sometimes, grammarly corrected to siphon?
They both fulfill the limerick rhyme rule anapestic,
Equally male by structure and, unclothed, not transvestic,
All have a wonderful snakey sound like a long slipery python.
You may think that I only tinker with dreary, drab syphons. So, while searching for syphon photos, I found a recent colourful photo of me Telemark skiing in my unique woollen onesie that was knitted by my dear mother when I was just a lad. I still ski in all weathers. Alas, we are both now oldfarts, the onesie will only go out with me with its ice-encrusted flairs in weather fair.
Tim
