Landscape Architect Articles

Water Feature Design07-01-04 | News

Water Feature Design

An Engineering Perspective
on Critical Components

By Amy l. Johnson, P.E., Aqua Engineering, Inc.

This photo of the water feature at Westlands Park in Greenwood Village, Colorado shows the channel and water wall on the left, spray jets around the drain grate, and water columns. Solenoid valve boxes located on the right side of the photo house the solenoid valves that operate the spray jets. The spray jets are activated by the green bollards on either side of the fountain area.

Whether you want a backyard Koi pond or a ?EUR??,,????'??Bellagio?EUR??,,????'?? style fountain, effective water feature design can best be accomplished through good communication between the designer and owner. An understanding of the desired aesthetic appearance, water effects, and physical interaction will need to be translated into design factors, and mechanical components capable of actualizing the owner?EUR??,,????'???s dream fountain.

Each desired effect associated with a water feature has either a direct or indirect relationship with a mechanical component of the system. Desired appearance, site limitations, and project limitations (such as construction budget) all impact the mechanical system design. An iterative process often develops in the design of a water feature. As an architectural or structural component changes, the mechanical system is affected and vice versa. A good understanding of how each discipline affects the other is crucial to moving the iterations forward and designing a feature that best fits the design team?EUR??,,????'???s goals.

This overview of the Runnels feature at the USA Today-Gannett Fleming Headquarters shows three narrow, connected channels leading from an upper basin down into the lake. Each channel includes a supply fitting and a return fitting. The main source of water is a pipe inlet hidden by rocks in the upper-most basin. Water from a lake fountain is recirculated through a pump in the irrigation pump station building.

Will the water flow through the fountain and drain away or will it be captured and re-used in the fountain? When water is re-used, the mechanical systems are often referred to as recirculating systems. Some fountains use little water and therefore recirculating the water requires a larger operation and maintenance cost than the cost of the water alone. In some instances, the potable water can be drained from the water feature and reused in another application, like an irrigation pond. However, most water features include recirculating mechanical systems to continually circulate the water and conserve on the overall water usage.

Critical Factors in Waterproof Systems

Waterproof lining options need to be considered for all water features. The method for waterproofing can affect the type of fittings installed in the fountain. Uncoated, reinforced concrete can be considered ?EUR??,,????'??waterproof?EUR??,,????'?? if it is at least eight-inches thick and water-stops are installed at all expansion and cold joints. Surface applied coatings are highly recommended to ensure the structure is waterproof and will not leak. Leaking fountains not only require additional ?EUR??,,????'??make-up?EUR??,,????'?? water, they often cause structural damage that will ruin the fountain or surrounding hardscape. Several surface applied coatings are available (usually an epoxy based material) and can usually be sprayed or rolled onto the hard surfaces. A variety of colors are also available.

A series of channels and weirs provide a break for people at the USA Today Gannett-Fleming Headquarters in Virginia. The total flow rate through the feature is 200 GPM, and each of three ?EUR??,,????'??runnels?EUR??,,????'?? has a water supply inlet (with a balance control valve) and return fitting to allow for field adjustments in flow over each weir. Unfiltered lake water was recirculated through the feature.

Impermeable membranes or liners also offer waterproof characteristics and can be installed in a water feature. Critical factors in selecting an appropriate membrane include whether UV protection is necessary, how the seams will be made or if seams will be necessary, and how repairs can be made to the liner in the future if damage is incurred.

A final epoxy or membrane surface may not be the desired visual finish. There are virtually limitless options for ?EUR??,,????'??hiding?EUR??,,????'?? or covering the linings to achieve both the desired aesthetic finish as well as an effective waterproofing method. Various types of stones, natural or man-made, can be used and laid over the surface. Naturalistic fountains, streams, or ponds can use liners that are completely covered by soil backfill with natural or man-made stones and planted vegetation for additional visual impact. Tile, glass, metals and other hard finishes can all be used to create the final appearance. Because some adhesives used to secure tiles or glass can cause deterioration of the membrane liner over time, the installation details of the waterproofing system and the finished fa??? 1/4 ade must be worked out during the design process to ensure the systems will work together.

Estimating Flow Rates

A replica of the Colorado River might be a design goal for a building entry feature, but the practicality of recirculating thousands of gallons per minute to accomplish this effect may cause the feature to be scaled back. In other words, the flow rate of the mechanical system will dictate the size of every other component in the system: from the pump and power requirements, to the nozzle and fitting sizes, to the filtration and water treatment capacities.

In this ?EUR??,,????'??trickle wall?EUR??,,????'?? feature, water spills over a 15-foot long weir and down the ?EUR??,,????'??roughened?EUR??,,????'?? stone wall at a flow rate of 80 GPM. A prefabricated filter and pump system is used. Two supply pipes (two-inch) with balance control valves are located in the weir basin at the top of the wall. Two return fittings along with water level controls and floor and overflow drains are located in the lower basin, which holds 16 inches of water.

A series of pools and weirs may provide the desired appearance while minimizing the required flow rate. Weirs can be used to create segments of rushing water over rocks while the stream between ponds may be less active.

Waterfalls and weirs require specific flow rates to establish certain effects. If a ?EUR??,,????'??clear sheet?EUR??,,????'?? effect is desired, the height of that clear sheet must be known. For instance, does the clear sheet extend from the weir to the water surface in the pool below or does it break up halfway down? The height of the clear sheet effect, and the construction of the weir edge, will determine the depth of water over the weir, and in turn, the flow rate needed.

Sometimes creating an actual scale model of the water feature is necessary to calculate flow rate. A water feature in Kansas City, Missouri included custom ?EUR??,,????'??bronze cast oak leaves?EUR??,,????'?? for water to spill over around a circular wall. The required flow rate could not be determined without an example of the leaf ?EUR??,,????'??open channel?EUR??,,????'?? which was not guaranteed to be consistent since each leaf would be hand-cast. Several models were developed to help measure the expected flow rate and extrapolate the total required flow.

Pressure Requirements

The pressure requirements associated with the mechanical system are based on hydraulic calculations of the water effects, friction losses and elevation changes. Some nozzles require 10 PSI while others require 50 PSI. If nozzles aren?EUR??,,????'???t used, this pressure component may actually be zero.

At Westlands Park in Greenwood Village, Colorado. Two independent recirculation systems were used: one for the channel/weir wall and columns and the other for the interactive ground sprays. The channels/weir wall and columns flow rate was 550 GPM, while the ground spray system was rated for a flow rate of 180 GPM. All water drained to an underground wet well, which both systems used as a water source. The interactive spray system included a high-rate sand filter and a programmable logic controller to trigger ?EUR??,,????'??random?EUR??,,????'?? sequencing of the sprays.

Friction losses are encountered as water travels through pipes, fittings, and nozzles. Pipe sizes and lengths throughout the mechanical system need to be accounted for during the friction loss calculations. If the friction losses are too great, the pipe sizes will have to be increased.

The elevation change to consider is not the vertical distance from the pump to the water level, but rather the vertical distance that the pump must ?EUR??,,????'??lift?EUR??,,????'?? the water. This distance is often the difference between the lowest pool water surface elevation and the highest water discharge elevation. When the water is stored in a buried wet well, that surface elevation is considered for these calculations. A pump that is located two stories below the water feature may only have an elevation ?EUR??,,????'??head?EUR??,,????'?? (required pressure) of two feet if the water is spilling from an upper pool to a lower pool through a two-foot clear sheet effect.

The recently remodeled Trumbo Fountain in the Student Union Plaza at the University of Colorado, Boulder campus includes 12 ground spray jets (mounted flush with paving stones). The programmable logic controller operates the sprays based on a timer sequenced with class schedules to provide the most ?EUR??,,????'??action?EUR??,,????'?? when students are in the plaza. The pavers are mounted on pedestals above a concrete floor with space between each paver to allow water to drain into a centered, buried wet well (hidden by the pavers). A flow rate of 120 GPM was provided to run all 12 sprays simultaneously. A UV (ultra violet) light was used for water treatment to help disinfect the water being recirculated.

The more complex the architecture or structure of the fountain, or the more complex water effects planned, the more complicated the hydraulics can be. Careful calculations of the pressure requirements will help ensure the desired effects can be achieved.

Controls

Several types of controllers can be incorporated into the mechanical system of a water feature to add flexibility and meet many needs of the system. Variable frequency drive (VFD) systems can be very effective when either the flow rate or the pressure may vary in the system. When a constant effect is desired, a constant speed pump is specified. In both instances, the pump controls can be programmed to operate on a timed schedule or from a signal that can be activated (a button, proximity sensor or bollard at the water feature). Wind sensors can be used to control the speed of the VFD pump so the height of a nozzle might be reduced when the wind speed picks up. Wind sensors can also be used to shut the mechanical system completely off.

The 24 spray jets at Mission Hills Park in Henderson, Nevada were installed flush with the ?EUR??,,????'??padded surface?EUR??,,????'??. A continuous trench drain around the feature conveys water back to the buried wet well. Adjusting ball valves upstream of the solenoid valves can produce different display heights for different jets (the jets in the yellow stars are shorter than the exterior jets in the red areas). Swimming pool water quality treatment systems were included to meet local health department requirements.

Interactive fountains may have intelligent controls referred to as ?EUR??,,????'??programmable logic controllers?EUR??,,????'?? (PLC) that can sequence the effects of the system to make it appear random or patterned. Additional controls can be included to operate the lighting effects or other components of the water feature.

Water Make-Up Requirements

Recirculation systems continually move water in the system and do need additional water to ?EUR??,,????'??make-up?EUR??,,????'?? for losses. Typically, these losses are due to evaporation, wind action, splash and people. Even indoor fountains will experience evaporative losses. Interactive fountains may even experience losses due to kids filling buckets and carrying the water away from the system.

An automatic or mechanical water level sensor should be included to monitor the water level and determine when additional ?EUR??,,????'??make-up?EUR??,,????'?? water should be added. Automatic systems can send a 24 VAC signal to a solenoid valve on a water supply pipe that will open and fill the fountain with water to the desired level.

Mechanical System Location

The location of the mechanical system should be known from the beginning of the design process. A building room or chase may be a logical location for a fountain mechanical system located in or near a building. An underground vault (usually constructed of either reinforced fiberglass or concrete) is another option and often preferred when trying to ?EUR??,,????'??hide?EUR??,,????'?? the system. OSHA ?EUR??,,????'??confined space?EUR??,,????'?? classifications and issues must be considered when a vault is designed.

Above grade, an access hatch and ventilation pipes are all that is visible of a mechanical system installed below in a buried vault, which houses a pump and filter system for a water feature in Pueblo, CO. One ventilation pipe serves as the fresh air intake to the vault while the other is the exhaust from the ventilation blower fan. The access hatch is lockable and access stairs are located on the wall of the vault.

For accessibility, maintaining adequate distance around each component is crucial. Valves need to be accessible. Pumps and filters may need to be worked on in-place. Mechanical components may need to be removed and replaced in the future, and provisions to do so should be anticipated during design. Will the equipment be removed through a door or hatch? Will it have to be dismantled first, or are their openings large enough to remove it in one piece?

For safety, electrical considerations include the location of the controls, accessibility, clearance in front of panels, grounding of all components, provision of GFCI (ground fault circuit interrupter) circuits and inclusion of shunt trip disconnect (to prevent operation of equipment in a flooded vault scenario).

Maintenance Considerations

Water features and their associated mechanical systems require maintenance. Some require daily maintenance where others may only require occasional monthly maintenance. Natural features like streams and lakes typically require less maintenance than an indoor reflecting pool where crystal clear water is desired. Typical maintenance activities include emptying the basket strainer, backwashing the sand filter, or changing the cartridge in the cartridge filter, observing the operation of valves and pumps to check for proper operation, lubricating components as necessary and checking for leaks or vibrations in the system.

This irrigation lake, at Indian School Park in Phoenix, Arizona, receives water from the Salt River Project, which is utilized in the landscape irrigation system through a pump station. A separate vertical turbine pump system also uses the lake water to supply a water feature at the adjacent amphitheater. The amphitheater pump system included automatic backwashing screen filters and had a flow rate of 600 GPM at 40-foot total dynamic head. The lake was lined with an impermeable lining system to prevent seepage. The weir shown in the photo was constructed from actual concrete blocks salvaged from the original Indian School site.

The design and layout of the mechanical system must anticipate required maintenance. Adequate room for movement and accessibility is key in making maintenance operations smooth and efficient. A system that is difficult to maintain is often ignored.

Seasonal maintenance may include complete shutdown and start-up procedures. Especially in climates that will freeze during winter months, the entire system should be drained. Start-up will include filling the fountain with water, annual maintenance of all components, and adjusting valves for proper operation.

Amy L. Johnson is a professional engineer and has over seven years experience as a hydraulic engineer specializing in water feature mechanical system design. She serves as a project manager and partner at Aqua Engineering, Inc. in Fort Collins, Colorado.