Replacing an antiquated and failing flood control system at Wisconsin's Hatfield Dam proved to be challenging. The selection and installation of hydraulic crest gates was cost-effective and withstood the test of a major flood that threatened downstream residents.

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By Scott Klabunde and Kim Hanson

Many early 20th century hydroelectric projects were built with wooden boards (known as flashboards) placed atop the associated dams as a means to pass floods. Flashboards were also installed to raise head at the dam and, correspondingly, increase power output.

Some such systems were designed to automatically release the flashboards when the headwater reached a certain elevation. Others were manually tripped by an operator, who physically removed flashboard systems as the water flow increased. All of these systems required an ongoing program to seal the inevitable leaks between the boards.

Flashboards were economical and easy to construct. However, engineering a system for safe and reliable operation was another matter.

Today, project owners are faced with the task of operating and maintaining systems that are a legacy of the engineering priorities of an earlier era. Hydroelectric projects now must adhere to strictly enforced state and federal regulations for water level, flow water level and flow regulations and respect the environmental and recreational interests upstream and downstream. Project owners must meet ever-higher dam safety and reliability standards and comply with Occupational Safety and Health Administration regulations.

As a result, many wooden flashboard systems have been upgraded. There are many alternatives available today for replacing outdated systems. North American Hydro, owner of the 7.2-MW Hatfield project on the Black River in Wisconsin, was faced with upgrading the outdated wooden flashboards that were part of the original project to a safer and more reliable system.

Background

The Hatfield project is in Hatfield, Wis., on the Black River, a tributary of the Mississippi River. The project's impoundment is named Lake Arbutus and comprises about 1,000 surface acres and 11,000 acre-feet of storage. Lake Arbutus is home to about 200 permanent residents, and its population swells into the thousands during the summer months. The Federal Energy Regulatory Commission issued a new 40-year federal license for the Hatfield project in , with guidelines requiring tighter reservoir surface elevations with stricter flow management goals, including minimum flows and recreational whitewater boating flow releases. Numerous additional regulations governing dam safety and structural performance are also part of the new license.

The project was originally commissioned in . It was configured with a principal spillway consisting of a 52-foot-high cyclopean concrete gravity rollway dam about 500 feet in length, topped with a wooden plank system and boardwalk. A major flood in resulted in the addition of a new gated spillway section at the project. The spillway consisted of 10 tainter gates, each 20 feet wide by 10 feet high. Both spillways divert the river into a 3-mile-long open earthen bank power canal to the generating station.

The newer gated section is normally used first to pass high flows. However, removing the wooden flashboards atop the gravity spillway was still necessary because the gated section's capacity was less than the 10-year reoccurring interval flood. Removal of the flashboards atop the gravity spillway required pulling about 5 vertical feet of horizontal boards of 8-foot lengths. As might be imagined, this is a slow, physically demanding and labor-intensive task. Reinstalling the flashboards often required a substantial lowering of the level of Lake Arbutus. At Hatfield, both the removal and installation process would be considered unsafe by today's standards.

The gravity overflow spillway retained its original wooden flashboard system through several ownership changes, as well as a project abandonment period.

The glacial moraine watershed of Lake Arbutus is conducive to periodic high flow conditions and flash flooding. Over the years, there were many instances when it was practically impossible to safely remove the wooden flashboards. Even if the flashboards could be removed, the vertical steel supports spaced for the 8-foot-long planking quickly became plugged with debris.

In , the adjacent town of Hatfield was flooded because the dam operators were unable to safely remove the flashboards in time. High flows, with significant amounts of debris, backed up along the wood and steel-framed system and boardwalk.

The resulting 7 feet of reservoir surcharge overflowed the rim, flooded Hatfield and ultimately breached the project's power canal.

In , after several million dollars were spent repairing the power canal, the Hatfield project was again generating electricity. However, due to concerns over the safety and reliability of the overflow spillway system, FERC required all flashboards to be removed and the reservoir to remain below the crest of the spillway. The lowered reservoir elevation curtailed both the recreational use of the reservoir and power generation. FERC also required the owner to improve the safety and reliability of the overflow spillway system.

North American Hydro purchased the project in , accepting the responsibility of upgrading the spillway under the commission's direction.

This upstream view shows the completed curb design at Hatfield Dam.

Design approach

The need to provide a safe, reliable flood control mechanism atop the gravity dam was obvious. But at a 7-MW plant, addressing this challenge economically was not so obvious. The system would have to be economically viable and would need to meet the following design criteria:

' Fail-safe operation. The system could not contain any failure modes that would restrict or prevent the gates from opening in the event of equipment failure or access issues.

' Minimum 40-foot-wide unrestricted discharge openings. This was required to pass large woody debris, even whole trees.

' Vertical clearance. Large trees tipping over the spillway crest require a large vertical clearance to overhead walkways or utility feeds.

' Safely operated. Operation from an overhead operating deck or walkway was considered unsafe for operating personnel due to the heavy and dangerous debris loading issues.

' Ability to close under full head. Lowering the reservoir to close the gates was unacceptable.

' Used only for flood flows. The project's adjacent tainter gate spillway would continue to be used for flow and level regulation purposes.

' Increase spillway capacity. Even if full utilization of the existing flashboard system could be achieved, the project's spillway capacity was marginal under current dam safety standards.

' Water tight. The system would need to seal tight without excess leakage.

Four options explored

To meet these requirements, several options were considered. They included:

' Stanchion gates: Initially, a system with vertical steel stanchions holding bays of horizontal wood was prepared. The system could be manually tripped by an operator, releasing adjacent sections simultaneously to achieve wide spill openings. However, this option was quickly abandoned. While it was economical, the manual tripping mechanism(s) contained several failure modes. It would be difficult to design a safe overhead operating deck high enough to be used effectively. The system could not be re-installed without lowering the reservoir and would leak.

' Rubber dam: This option was considered desirable for several reasons. Clear-spanning the entire 450 feet would have provided the widest possible uninterrupted discharge passage for debris and maximum flow capacity. Additional spill capacity could be achieved by cutting the gravity dam crest down to accommodate the tallest and deepest rubber bladder design available. But the inability to control or direct the flow was a problem. Two siphon-set generating units were installed at the base of the right side of the gravity dam in to convey the license-required minimum flow to the main river channel. Subdividing and sectioning the rubber dam to accommodate these units would have added substantial cost and was counterproductive to maximizing spill capacity. Concerns were raised regarding the longevity, warranty and source of a suitable rubber bladder.

' Obermeyer gates: The Obermeyer design consists of a steel gate system that is hinged on the bottom that overhangs an inflatable air bladder. The system could be sectioned for discharge control and appeared to be a more reliable and/or robust choice than the rubber bladder alone. It could also accommodate a deeper and taller gate to maximize spill capacity. The potential for ice build-up on the seals or individual panels was not a concern because the local community was endorsing a seasonal reservoir drawdown, meaning the gates would not be used in the cold weather months. But the higher cost of the Obermeyer design became a factor.

' Hydraulic crest gates: Hydraulic systems are well-known and understood. A hydraulic system could keep costs down by allowing the use of local contractors for construction. Each gate could be operated independently and remotely, without an overhead operating deck. The intermediate piers needed to support these gates could be kept relatively small in width and not unduly reduce the usable spillway width. The system would have good sealing mechanisms. The hydraulic system could be designed to 'fail-safe' with an inherently low risk of failure to open during a major flood. A simple valve located in the remote hydraulic power unit control house could be manually operated to redirect the flow of hydraulic fluid and allow the weight of the water to lower the gate. The steel crest gate height could be designed to accommodate any depth cutoff of the gravity dam crest for additional spill capacity.

During the design phase, North American Hydro determined that saw-cutting and reconstructing the upstream approach edge of the gravity crest would allow the engineer to design the most efficient design discharge configuration.

Also contributing to the decision-making process was the fact that North American Hydro has operated a hydraulic crest gate system at another high-hazard dam since . During the intervening years there have been few, if any, operational problems. In the end, the hydraulic system was chosen for Hatfield.

A rubber compression sill seat at Hatfield Dam was built to ensure a tight seal when the hydraulic crest gates need to be closed.

System details

The fabrication and installation of the gates were contracted to Gerdes Manufacturing, a local contractor. The 450-foot crest of Hatfield Dam was configured with nine gates, each 45 feet wide and 5.5 feet high and having a curved skin plate radius of 17.5 feet. The gates are separated by concrete piers, each of which is 3.5 feet thick. Between the concrete piers, four cast iron supports or saddles were anchored to the gravity dam. The crest gate torque tubes are 12 inches in diameter and have raised machined stainless surfaces riding in the cast saddles.

The gate side seal material is reinforced rubber that is permanently attached to the concrete piers and field-matched to the curved gate skin. The hydraulic rams pull the gate into the seal and maintain sufficient pressure to seal each side of the gate. The bottom seal consists of a reinforced rubber compression seal between the upstream curb and the bottom edge of the gate as it closes.

The system is designed to be used for flood control with only two gate positions: fully opened or fully closed. Each gate is driven by two hydraulic rams, one on each end. The curved gate skin and supports are designed to withstand the failure of a single ram without damaging the gate. A counterbalance valve is provided, and a proximity switch is installed at each end of the ram's stroke for position feedback to the hydraulic power unit (HPU) and programmable logic controller (PLC). The PLC continuously monitors the position of each ram and makes adjustments to assure equal movement and maintain proper alignment of each gate. This corrects any drifting and adjusts for gate misalignment that could twist and damage the gate. The system operates on 1,000 psi.

The HPU, PLC and controls are located in a control house adjacent to the gravity dam. The HPU cabinet panel has individual controls for operation of each gate. Backup power is provided by a diesel generator and automatic transfer switch. Additionally, a fail-safe feature allows the operator to manually defeat each individual gate's counterbalance valves. In the event of a malfunction, the hand pump, located at the HPU, can be used to defeat the counterbalance valve pressure (about 200 psi). The weight of the water will allow the gate to close. The HPU was designed with the appropriate heaters and water/condensation separators and filters.

A mineral-based hydraulic oil was initially chosen for the system's fluid. Considerable design effort was spent on the layout of the fluid lines, the choice of material for the lines and connection method to be used.

The hydraulic lines running from the HPU to each of the gates were routed along the crest of the dam, downstream and behind the gate torque tube support hinges (or 'saddles'). Tucked away under the steel gate, the lines are protected from water and debris. Intermediate gate piers were formed atop the gravity dam to allow the lines to be routed from pier to pier. The hydraulic lines are further protected by being run through the interior of the piers to their respective hydraulic rams. The ¾-inch-diameter hydraulic lines are made of stainless steel to preclude any failure modes associated with corrosion. Additionally, the lines were fabricated in continuous runs of welded construction. The number of connections was kept to a minimum to reduce the potential for leaks. The hydraulic line runs located atop the crest, immediately downstream of the gates, were covered with a removable aluminum plate to provide additional protection. It was later decided to fill the system with a more environmentally-friendly biodegradable blend of high oleic vegetable and synthetic polyester-based oil commonly used in food-processing plants. The system was started up and tested using the biodegradable oil.

The Hatfield Dam crest gate project was completed in , to improve safety of the dam during high flow events.

Construction

In an effort to keep the costs down, North American Hydro provided its own management of the contractors and vendors involved with construction of the system. In the autumn of , and in anticipation of construction scheduled to start in the following spring, the level of Lake Arbutus was lowered even further. Additional lowering of the reservoir was necessary to facilitate removal of the old steel flashboard support structure and the saw cutting of the crest and removal of the sawn concrete. The saw cut would allow maximum room for the gate hinge mechanisms without unduly sacrificing spillway capacity.

The saw cut would also provide a clean, level surface on the dam crest in preparation for installation of the concrete piers and the hinges (or 'saddles') on which the gate torque tubes would rotate. A diamond wire rope saw-cutting process was used to remove almost 3 feet from the height of the crest. A series of 1.25-inch holes were drilled horizontally through the dam at the 3 foot depth, every 10 feet along the crest. The wire saw-cutting apparatus was then anchored to the upstream side of the dam, and a horizontal cut was made every 10 feet, followed by a vertical cut. A barge-mounted crane was used to remove the cut concrete pieces from the dam.

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The saw cut revealed a valuable structural feature that had previously been unknown and did not appear in any construction reports or on any construction drawings. The gravity spillway is designed with very strong and large vertical keyway control joints located at 50-foot intervals.

Over the winter months, local contractors began fabrication of the gate torque tube supports (or 'saddles') and the nine crest gates, as well as the assembly of the HPU and control system. A local contractor was also chosen for the civil work related to forming and placing the concrete piers. Construction began soon after spring runoff.

The pier design utilized the contractor's standard bridge forms, eliminating additional expense associated with (what would have otherwise been) custom-designed forms. Spillway discharge efficiency was maximized by designing the upstream approach curb with an 18-inch radius, utilizing the optimum design coefficient.

This was a critical aspect in achieving an additional 20% spillway capacity. After the upstream steel curb was placed, the piers and saddles were anchored in the gravity dam as per the design specifications. The brackets for attaching the hydraulic rams to the piers were set and aligned, and the hydraulic rams were mounted.

The steel crest gates were delivered on a barge-mounted crane and placed on their respective saddles, with each side connecting to the hydraulic rams. Simultaneously, the stainless hydraulic lines were being installed along with the HPU. The system was tested and placed in service in .

Hatfield Dam and its new hydraulic crest gate saw a major real-world test in , when a historic flood struck the area. Although downstream residents prepared for the worst, the dam and its crest gates performed as designed and kept the town of Hatfield flood-free.

The test: The historic flood of

The new hydraulic system did not have to wait long for its first major operational test. In , Hatfield experienced a historic flood ' the second largest on record. The 500 Hatfield residents who were evacuated from flooded residences in were preparing for the worst.

However, this time the results were much different. The system operated exactly as designed, using all nine of the crest flood gates. Community residents breathed a sigh of relief when no flooding occurred there. All involved in the spillway project upgrade were rewarded with the satisfaction of knowing they had produced a reliable product that delivered exactly what was promised.

On March 28, , the majority of North American Hydro was purchased by Eagle Creek Renewable Energy, which is based in Morristown, N.J. At this time, additional wood flashboard system upgrades are being planned within the North American Hydro/Eagle Creek Renewable Energy portfolio of projects.

Scott Klabunde is vice president of operations for North American Hydro. Kim Hanson, PE, was design engineer with Mead and Hunt for the Hatfield Dam hydraulic crest gate project and is now with MWH Global.

Your Guide to Driveway Gates

Driveway gates are installed in homes and businesses for a variety of reasons. Whether your primary concern for installation has to do with architectural design, aesthetics, improved security, or privacy, you should still consider a variety of points when choosing a driveway gate installer.

Your preferences in design elements, driveway gate types, materials, operation, and even the accessories you want can all influence the final design. To help make your decision easier we have compiled an overview of options that we hope will make it easy to choose the right gate materials and setup for your home or business that's effective, safe, and easy to maintain.

Types of Driveway Gates

Hillside installed single slide glass and steel driveway gate

Horizontally clad exotic wood sliding driveway gate

Wrought iron and sheet metal sliding driveway gate

One of the first decisions to consider with a new driveway gate is the type of gate you want. The material you use largely influences things like design, function, maintenance requirements and even the size of the gate you want to install.

Common materials used in stock and custom driveway gates include:

• Steel ' Most driveway gates are made using powder-coated steel which is chosen for it's ease of manufacture and customization. It's also highly durable and sturdy making it a good choice for long-term use and improving home security.
• Iron ' Like steel, iron driveway gates are highly durable and have a certain feel to them that some people prefer for their home exteriors. Like steel gates, iron requires some upkeep and maintenance.
• Aluminum 'Aluminum is sometimes a preferred choice for driveway gates. Even though it isn't as durable or sturdy as some other metals, aluminum is lightweight making it ideal for larger gates without as much worry over sagging or misalignment. Aluminum is also more affordable and is highly resistant to rust.
• Wood ' This is a great material for driveway gates, especially if you want more options for customization and design. There's a lot you can do with wood to change the design, right down to the type of wood you choose for color and texture variations. The major downsides to consider with wood is that it's considerably heavier, can be more costly, and wood is prone to cracking and warping ' that means more frequent maintenance.
• Glass ' In the last few years we've started to see the introduction of glass on auto and pedestrian gates. Glass is an elegant material and can be very contemporary or provide a transitional look. We can sputter gold or silver onto glass material for a sophisticated finish or we can finish the back of glass pieces in almost any color to create a truly one of a kind look. Like most gates, we start with a steel frame and all glass gates are finished on the property.

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Design Elements to Incorporate

Rust stained Moroccan inspired bifold gate

Horizontally clad exotic wood sliding driveway gate

Wrought iron and sheet metal sliding driveway gate

The design of your driveway gate is less about functionality and more about the aesthetics. While you may not initially be concerned with the look and curb-appeal of your gate design, there's one thing to consider.
A well-designed driveway gate that fits the ambiance and architecture of your home, while tying in and complementing features of the property and landscaping, will increase the property value of your home.

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Driveway gate design includes:

• Custom designs around themes ' Often gates are designed to match a certain architectural style such as gothic, European/versaille, contemporary, and even traditional western designs. The design style is often cultural, or you can choose a completely custom gate design such as one that incorporates a family crest, logo, or other feature.
• Color ' Options for color customization are fairly broad. For wooden driveway gates you'll find color variations in the type of wood used, and of course wood can always be painted or stained. With metal driveway gates such as those made from steel it's easy enough to get them powder coated in the color you like.
• Shape ' Driveway gates can be customized to just about any shape or design. For most homeowners, residential gates are designed with vertical pickets within a frame. Outside of that you see some common themes in the shape such as the flat top (a simple rectangular gate), arch-top gates (with a gradual but smooth arch) and arch-top gates with finals (pickets that extend beyond the top like points)

Multi stained medallion gate toppers

Intricate hand forged wrought iron

Stainless Steel Gate Design

Custom medallion

Hammered steel and gold tinted medallions

Custom steel gate and inserts

Heavy duty automatic driveway gate operators

How Secure are Driveway Gates?

The security of your driveway gate has everything to do with the type of gate you install, along with the materials and accessories.

For example, a short and simple manually operated metal driveway gate offers only the most basic security when it's closed and locked.

If you were interested in maximizing security along with safe operations and easy entrance and exit you may want to consider an automatic metal driveway gate that uses accessories such as coded entry, magnetic locks, sensors for vehicles, and cameras and intercoms to effectively control inbound and outbound traffic.

Common Accessories for Driveway Gates

Security gate entry via keypad

Holovision network controller for secured gate entry

Visually stunning driveway gates go a long way to compliment your home or business, but you're not limited to that. You customize a lot more than just the design. Driveway gate accessories can be purchased to add more functionality, safety, security, and ease of access to your property.

Some of the most common accessories include:

• Wireless intercoms ' An intercom system on your driveway gate allows you talk to visitors without leaving your home, and because it's wireless there's minimal installation requirements.
• Card readers ' Proxy card readers let you grant access to anyone holding the card. These can be ideal for quick entrance access, especially where you can also program proxy card readers for the doors of your home and business to make keyless entry a breeze. You can even track who is coming and going.
• Pin pads ' Basic security on a numerical pad and mounted box that requires a passcode to be entered in order to open the gate.
• Sensors ' Various sensors can be installed with different functionality including motion detection (for light and video activation), Photo beams (for safety and to eliminate entrapment), vehicle sensors (for entrance and exit without exiting the vehicle).
• Programmable timers ' Timers can be added to automatically shut down and lock the gate, or open it, during specific windows of time.
• Maglocks ' Magnetic locks or solenoid locks can hold a tremendous amount of force, upwards of lbs, when electronically engaged. They're far more secure than generic locking mechanisms.
• Remote entry ' Set your driveway gate up with remote access so it can be opened or closed/locked via your .
• Solar panels ' Install a driveway gate that runs on clean energy to power your accessories

What to Consider When Choosing and Designing a Driveway Gate

Having a professional install a driveway gate can be as simple as selecting a stock gate and having it installed, but in most cases there are plenty of things to consider as part of the installation process. You're not on your own though. When you choose a professional installer they'll walk you through the information to help you choose the best gate to meet your needs.

Things to consider when planning your driveway gate purchase and installation include:

• Materials ' Think about how you want your gate to look, the amount of maintenance you can handle, the size and weight of the gate, color, and if you want custom designs. Remember, wood is heavier so it's not ideal for larger gates. Steel is more durable but costs more than aluminum. A professional security gate installation company will help you make the right choice of materials that fit the style and topography of your property.
• Functionality ' Are you installing a gate purely for security purposes, is it to enhance the curb appeal of your home? Maybe you just want to maximize your privacy. Answering those questions can help you determine if you want a swinging gate, a sliding gate, one that's see through, or one that completely blocks the view of your property.

Black wrought iron pedestrian gate to the left and matching automatic driveway gate on the right

• Accessibility ' This is a big one to think about. You need to decide if you want your gate to be a manual or automatic electronic driveway gate. Will you need more than one gate for a wraparound driveway, or perhaps a pedestrian gate for walk-through access or a door built within the gate itself. Do you need hands-free access to open and close/lock the gate?
• Additional contract work ' Depending on the gate you may have the need for additional contractors such as landscaping, electrical, masonry, etc. A good professional installer will be able to provide the necessary contacts with contractors they know and trust.
• Safety ' With any gate you want to ensure safe operation, and this is especially true of electric gates that open and close automatically. Consider pets and children in and around your property and what kind of safety features you'll need, at a minimum, to ensure everyone's safety. The Consumer Product Safety Commission has minimum requirements for safe operations. If you're not installing a driveway gate with quick access for emergency personnel, know ahead of time how they'll be able to get access in an emergency. Your installer should be able to help guide you to code requirements in your community, many of which require emergency access boxes.

Working with Professionals for Installation

Installing a driveway gate shouldn't be treated as a DIY expansion to your home. It's best left to an experienced contractor who can manage the full spectrum of skills needed to complete a gate install including security hardware and software, electrical, landscaping, metal fabrication, footing, and masonry work. This greatly reduces the chance of hardware failure or an improper installation, which can lead to abnormal wear and costly driveway gate repairs.

Your driveway gate installation professional will take you through critical steps to ensure that nothing is missed, allowing them to plot the course of the work and provide an accurate estimate for getting you the driveway gate that best fits your needs. Here's what you can expect when working with a professional:

• Step 1 ' Meet with your contractor for a design consultation to review needs and answer questions
• Step 2 ' Review design ideas along with material recommendations and accessories
• Step 3 ' Review estimate for installation which will include managing any necessary contracted specialists
• Step 4 ' Sign agreement to authorize the agreed upon work to begin
• Step 5 ' Property preparation, setup, and fabrication which could include grading and ground levels, holes, wiring, and any custom gate designs
• Step 6 ' Installation and testing of all functions including safety elements, locks, and other accessories. This also includes alignment and leveling for proper operation.

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