It may seem really basic, but it’s extremely important to know how to properly excavate a pond. We all know that a contractor can dig a hole, but do you really know the benefits of doing it right? A step-by-step excavation process will undoubtedly save you time, money, materials, and headaches.
Before you begin digging, you’ll want to perform a few easy tasks which will help to avoid surprises later on. First, be sure to assess the property where the pond will be located and take note of all the existing structures and utilities. Second, using a site or laser level, determine the high and low areas where the pond will most likely be positioned. This gives you a better idea of any obstacles or challenges you might need to overcome when installing the pond.
Remember to also look at construction access points for the property; this will help you determine your options for the excavation process. Are there any gates, narrow walkways, or steps that would block equipment access?
As you walk around the pond perimeter, determine the high and low areas in relation to the main viewing area. Most ponds are located next to a patio, so the patio would be the starting point. We like the water to come right up to the viewing area and typically set the water level two to three inches below the level of the patio. Once the water level is established, make the entire pond perimeter a minimum of 2″ above the water level. At the back edge of the pond where the waterfall is located, the level would be much higher, depending on the final waterfall height. All measurements taken from this point forward will be in direct relationship to the water level.
Most properties have a gentle slope going away from the home for water drainage. Be sure to adjust your calculations to compensate for this slope. In severe situations you will need to bring supplemental soil to the project to create the desired elevations. If the slope is coming towards the home it will allow you to create dramatic waterfalls, but it will also increase the time of the excavation and the amount of soil generated.
Why Build Ledges
When you begin your pond excavation, be sure to include ledges along the perimeter. If someone were to accidentally or purposefully walk into the ponds, you want to avoid a dangerous drop-off. Ledges act as a safe staircase as opposed to a slippery slope. They also add strength and stability to the pond. Terracing is much more stable and less likely to collapse than a steep, tall wall.
In addition, ledges provide aesthetic appeal. If you create a proper ecosystem pond, the water will be clear and the pond floor is visible. Ledges provide layers and contours, adding interest to the pond’s interior. Pond ledges also provide shelves for aquatic plants; different ledge depths are perfect for planting the many different species that are available. For example, marginals will grow in 1 to 12 inches of water, while water lilies and oxygenators prefer 12 to 36 inches of water.
The first pond ledge is typically 6 to 10 inches deep and should be dug around the perimeter of the entire pond. Remember, this ledge should be covered in gravel, so a ledge that is six inches deep will become a ledge that’s four inches deep after the gravel is installed. Ledges can vary according to their usage, but they do not have to be perfect. The goal when creating a pond is to copy nature, and natural ponds don’t have perfectly level or symmetrical ledges graduating towards the bottom of the pond. When the first ledge is completed, you can mark out the next area to be excavated.
Remember that the vertical walls of the ledges will be covered with boulders or larger rocks and the flat areas will be covered in gravel. If you will be using all hand-placed stones, make sure you keep your ledges to a maximum of 12 inches tall; otherwise you’ll be stacking multiple rocks on top of each other which will increase the allotted amount of time for stone placement. Ideally, use one or two rocks to cover the vertical walls. If you have equipment on site you’ll have more freedom to use larger boulders to create deeper ponds with taller vertical walls, but the price needs to reflect the additional costs incurred by the increased time and materials necessary to complete the task.
The width of the ledges should also vary according to the pond design. A good rule of thumb is to use narrow ledges of 6″-10″ wide in the foreground, and wider ledges 16″-24″ in the background. The reasoning behind it is simple; the foreground area (adjacent to patio/viewing areas) is the area where your clients will be feeding and viewing their fish. This allows ample space for the fish to get up close to their owners.
The background area is the zone where the pond will transition into the surrounding landscape; the wide shallow ledges are perfect for mass plantings of aquatic plants to help with this transition.
Consider the Waterfall
The other area that needs careful consideration is the point where the stream or waterfall enters the pond.
The waterfall, or stream, is a very important section for many reasons from aesthetics, function, and costs. From an aesthetic point of view, what type of water entry point is desired? A large dramatic waterfall or a small riffle zone?
The depth of the water at this entry point has a major impact in the success of the design. If the water is deep at this point it will dictate the size of the boulders necessary to frame the waterfall; it will also change the sound of the waterfall (deep=base tones, shallow=treble tones).
Shallow water at the entry point of a swift moving riffle area will create a natural rippling effect on the water’s surface and it will aid in the overall pond circulation. Defaulting to shallow water near the waterfall or stream entry gives you the greatest amount of options.
From a function and cost standpoint, deep water near the waterfall requires larger boulders and a greater amount of time. Water quality is typically better with shallow water as it will help with overall pond circulation and debris removal.
During the excavation phase, the filters and piping are laid as well. The biological filter is always set first, and the flexible piping follows. This is important for peak efficiencies of the crew. The excavated soil can be used to create a berm around the biological filter and its size should be equivalent to the size of the pond. In other words, if the pond is 11′ x 16′, and 2-feet deep, the berm should be 11′ x 16′ and 2-feet high.
If the biological filter is set higher, more soil will be needed to disguise it and may seem out of place. If it’s set lower, the berm will need to be more spread out in order to use the soil. Each site should be evaluated as to how high or low the waterfall should be. Soil usage is often an overlooked part of the construction process and you don’t want to be left having to remove soil from a project.
If the quality of the soil is poor, organic topsoil can be brought in to be used for future plantings. The larger and broader the berm, the easier it will be to naturally incorporate plantings to help a water feature look as natural as possible.
Challenges of Poor Soil Conditions
Digging can be fun, but there are many soil types that can cause all sorts of pond excavation challenges.
Clay Soil: Spring and fall are the best times for excavation because the clay is softer, while mid-summer requires a pick-ax to chisel through the hardened clay. Clay soil in certain areas is notoriously bad and the selling price of the job should reflect the extra time needed to complete the excavation in difficult soil.
Rocky Soil: In addition to longer digging time, rocky soil has other challenges. One of them is a hard sub-surface to deal with after the digging is complete. In this instance, you can lay down several layers of underlayment to act as additional cushion under the liner. In severe cases, place a layer of the fabric on top of the liner where larger boulders will be set.
Bedrock: Bedrock is the toughest because it takes much longer to dig than any other soil conditions. Depending on where the rock layer is found, the pond may need to be built completely above grade, or half and half. The deeper you can dig, the better the pond will look. It’s tough to make a pond look natural when it’s sitting 18″ above the surrounding soil. In certain parts of the country, jackhammers are a necessary piece of equipment. It’s the only way to cut through the hard layers. It can be a slow process, but extreme conditions call for creative solutions.
Sandy Soil: In sandy, loose soils the digging is a piece of cake, but it’s almost impossible to cut a ledge into it. The easiest way to handle this problem is to dig the pond with a flat bottom, with the side gently sloping into the middle. Once the pond is dug, you have two options: Place boulders on the sloping sides, and put gravel on the bottom – or place boulders on the bottom and backfill behind the rocks creating gravel and boulder terraces. Planting areas and irregular ledges can be created with this method.
Considerations for Large Projects
On larger projects of 600 square feet or more, large equipment is needed to help with the excavation, large boulder placement, and material handling. Once the decision is made to bring in a piece of machinery, you can take full advantage of it.
Skid-steers and backhoes are the two most common pieces of equipment, but cranes and loaders can be used as well. A skid-steer can be effective in excavating the top shelves of the pond, but the bottom and final shaping should still be done with hand tools. A good backhoe operator can maneuver around enough to do quite a bit of digging, but some handwork is still necessary to clean things up. If you don’t own heavy machinery due to cost, you can subcontract the machine work. The cost of the subcontractor is calculated into the price of the project.
Whenever heavy equipment is added to a project, remember to add additional time to the project for equipment damage to the surrounding property (ruts, compacted or destroyed turf) that will need to be repaired, or at the very least discussed with the clients.
Sometimes there is a little more to excavation than meets the eye, but it’s still fairly basic and just requires some common sense. If you start your project out right and avoid creating extra work for yourself, everything else will fall into place and you’ll undoubtedly save time and money in the process.