Important Installation Considerations

Safety    Large pipes and taller inlet structures can present safety risks.  High head pressure combined with large water flow can create significant suction forces that could pull people or animals into the drain.   Use appropriate fencing and safety grates to prevent accidental access.  

Floating and Leaning are the design factors that affect single-sided flashboard riser structures.  

Leaning   The weight of soil behind tall structures can push on the back causing the structure to lean forward.  

Floating     Single-sided box-type flashboard inlet structures want to “float” when the water is blocked and the inlet box is dry.    Water weighs 62.4 pounds per cubic foot so the floatation force is equal to the cubic feet of water displaced by the box times 62.4.

All structures will resist floating to some degree through a combination of their weight and soil trapped against the sides and the pipe flange. Floating becomes a significant problem on large and tall boxes where the floatation force can reach thousands of pounds.  Additional ballast can be added to counteract the floating force.  The density of these materials varies with moisture content and the degree of compaction.   Conservative estimates of does it for some likely ballast materials are:

Gravel                              89   lb/cuft
Sand                                90   lb/cuft
Compacted clay soil        95   lb/cuft
Aluminum                       172  lb/cuft
Concrete                         140  lb/cuft
Steel                               490 lb/cuft

Multiply the Width x Depth x Height of the inlet box to get the cubic feet of water displaced.  Multiply this by 62.4 to get the floating force.   Divide the floating force by the density of the ballast to get the minimum number of cubic feet required.

There are optional methods to secure ballast to  the inlet box:

The bottom section can be fastened to a user-supplied concrete footing pad with lag bolts.   The volume of the footing pad should be roughly equal to the volume of the inlet box.

We offer  frames that can be added to the inlet structure that utilize soil behind the structure to secure it.  These frames prevent both floating and leaning.   The frames also provide structural support for the pipe and coupling.  These frames are fitted with anchor points that align with pre-cut holes in the inlet structure.   Backfilled soil or gravel serves as the ballast.  We offer optional skirts for the frames to stabilize the backfilled soil.  

Sealing In-Line Stoplogs

Achieving a watertight seal is difficult, especially in tall structures with high head pressure.   Don't become obsessed with the seals because small leaks simply do not matter in most cases.  

We never thought much of the little leaks until we decided to sell units.   We measured a competitive in-line unit and found that it leaks.  Their instructions confirm that some leakage is normal.  We measured their leak rate to consistently be 0.2 gallons per minute on a 6" X 48" structure.  We repeated this test under multiple conditions while making our best efforts to achieve zero leakage.  This low leak rate does not seem like much but it adds up to 105,000 gallons or 3.8 acre-inches per year.   But, as incredible as that number might sound, it is not a lot when considered in context with most pond applications and it only represents about 0.04% of the maximum flow capacity of a 6-inch pipe -- a very small percentage of the maximum.  Ironically, our initial designs leaked at a similar rate.   We did observe water weeping very slowly from some of the screws on the outside of the competitive structure.  Our unit is completely welded and will not leak in that manner.  

While there are applications where this might matter like pooling a slow spring or regulating soil water level in an arid garden, we would first suggest that other level control methods might be better suited in these situations.    But, we are perfectionists and obsessed with creating a rugged seal that eliminates leaks.  We will never say zero leaks but our units can achieve a very tight seal with a little diligence (only measurable in drips per hour).  

Sealing Flashboards

Most flashboard riser applications can be effective even when they leak like a sieve.  In most cases, we recommend placing 2x6's in the slots and driving a small wedge in the top to hold them in place.   Wooden flashboards made from ordinary lumber do not provide a perfect seal.  They will leak a little bit when first installed.  They will naturally swell and seal up with mud, algae and debris in a short time.   The small amount of leakage is not a problem when ample water flow is available.   The boards will leak for a while then seal up and slow the leak to a small amount of seepage.   

If necessary, an immediate watertight  seal can be achieved by using the widest possible flashboards and placing sealing material between the flashboards.  It is common to apply caulk or gaskets between the boards to achieve a better seal.

    

Water pressure can generate surprisingly large forces on the lower flashboards and the structure in general.    These forces multiply with the width and height of the structure.   Lower flashboards in a tall structure will experience higher pressure and demonstrate a greater propensity to leak.  The lower flashboards can be difficult to remove on wide or tall structures.  

We offer optional flashboards that resist swelling and have integral seals and handles.   We also offer optional weighted top boards to prevent wooden flashboards from floating.   These are called "sinker" boards.   Sinker boards are made of steel tubing filled with concrete. A sinker board can be installed on top of regular wooden boards to prevent them from floating.   A permanent sinker board is often used as the bottom board to maintain the bottom seal.  

Sealing Large Diameter HDPE Pipe Connections

Our in-line units are provided with sealed couplings.  Even with properly sized couplings, achieving a truly watertight seal is difficult with corrugated pipe couplings.   The seal is not critical on the outlet side because the coupling is not under pressure.   Leaking can be a problem on the inlet side of an in-line structure if the seal is not watertight. The problem is magnified on taller structures with more head pressure.  An optional step involves applying an adhesive between the pipe and the inlet sleeve on our in-line unit.   Few adhesives adhere well to polyethylene.   We recommend a liberal coating of Dupont (formally Dow) U-418HV, U-428HV or U-438HV urethane  adhesive on the inlet sleeve prior to final installation of the pipe.  These single-part adhesives cure into a tough but pliable urethane rubber.   The glue does not truly bond to the HDPE pipe but it makes a great form-fitted gasket.   Use caution because these adhesives are tenacious and are hazardous.  They make a mess of everything they inadvertently touch.   They do not wash off.  Wear disposable gloves and protective clothing. Follow the manufacturer’s instructions and wear the appropriate PPE. 


Corrosion

Galvanic corrosion is a significant problem for metal structures.    Everyone knows steel rusts.  Aluminum also corrodes and deteriorates.  Corrosion is an electro-chemical reaction that is magnified with salt, acidity and chemicals in the soil and/or water.   Corrosion can become extreme when dissimilar metals are present.   Corrosion varies widely with the application environment.

Coatings can provide some protection but will not prevent eventual corrosion.    In some cases, coatings can magnify the problem by concentrating electrical currents near areas where small defects are present in the coating.  Coatings can also hide corrosion, delaying maintenance until significant damage is done.    All things considered, a good coating is beneficial but not an absolute guarantee to stop corrosion.

We prefer plastic pipe because it does not corrode or promote galvanic corrosion of the drain structure.  We have dug out lots of heavy galvanized steel pipe that has been completely eaten away by corrosion.  

Our aluminum structures will resist corrosion in normal soil conditions and provide a long service life.  

Do not install our aluminum structures where they are in direct electrical contact with steel — the aluminum will become a “sacrificial anode” and it will corrode.  

We have uncoated steel structures that have been in the weather and exposed to freshwater for years without significant corrosion problems.  The steel forms a patchy rust mostly around cut edges, welds and fasteners.  It eventually develops a patina and remains stable for many years.

Sacrificial anodes can be used to help protect steel structures.  A wide variety of materials and configurations are available in the marine market.  We offer optional sacrificial anodes that can be directly bolted to our structure.   These anodes will eventually corrode away and must be replaced occasionally.   This article does a nice job explaining sacrificial anodes:

https://www.absolutemarine.co.nz/image/catalog/documents/anodes/truth_aluminum_anodes.pdf?srsltid=AfmBOoprWqX3AYXFg8qYlC2ZZEZKmLGU7KzVcltH5hDYjV7QGlWhfCNs