Richland Soil and Water

Make sure to consider the total overall width of the dam. This includes not only the top width, but also how far the inside dam toe and outside dam toe will extend. Example: a 6’ high dam with a 2:1 inside side slope and a 3:1 outside side slope and a 8’ Top Width, would take up 38’ of total width!

Mark where the water level of the pond will be during its normal elevation.

Mark the water level where the pond water will be overflowing out of the emergency spillway.

Mark where you will outlet the principal spillway and mark where the emergency spillway will be located.

Topsoil is a valuable resource. In nature it can take over 500 years to form an inch so you do not want to waste what you have. Before excavation begins, the first step should be to have the topsoil stripped off any areas where digging will happen. The topsoil then should be stockpiled in an area where it can be retrieved when construction is complete. It can then be re-applied to all areas to be re-seeded. The new seeding will have a much better success rate if it is established in topsoil rather than unfertile sub-soil.

Often ponds are excavated in an area not conducive to a pond, such as wooded areas or reclaimed land. It is crucial to remove all rocks, tree roots and vegetation from the dam area as well as the emergency overflow to be able to achieve good compaction.

Compaction is a very important practice in pond construction, especially when constructing the core trench and dam. Proper compaction is achieved from 3 main components: Soil type, soil moisture and compaction method.

The soil should contain a mixture of all silt, clay and sand to achieve the best compaction. A mixture too high in clay will make it hard to obtain the proper moisture content, become too sticky if too wet and when the soil dries out it can shrink and crack, creating potential leaks. Too much silt and the soil will not compact together at all, it will spread out during compaction rather than building up higher and higher. If a soil has too much sand, it will also not compact, and it will also allow water to move through it too easily.

A good guide to soil moisture content can be obtained from a simple field test. When soil moisture is at the best level for effective compaction, you should be able to roll the soil between your palms into a thread (about the thickness of a pencil) that just begins to crumble on further rolling. If the soil thread crumbles before it reaches pencil thickness, it is too dry. If the thread can be rolled to a thickness much less than a pencil, then it is too wet.

As far as compaction methods are concerned, the soil used to build the core trench and to form the embankment should be placed in 6” layers, with each layer thoroughly compacted before the next layer is placed. A layer of more than 6” of soil before compaction is not recommended. The number of passes that should be made by the compacting equipment depends on the soil type, but it should be at least four. Preferably, compaction should be achieved with a sheepsfoot roller. However, a heavy rubber tired machine or a loaded pan may be satisfactory, depending on the soil behavior and the layer thickness and the ability to compact the entire surface. (Bulldozers do not offer adequate compaction.)

A core trench can reduce the chances of water seeping underneath the dam. A core trench may be built along the entire length of the dam. To create a stable core the trench should be at least 3 ft deep and no steeper than 1:1 and the width of the equipment used. The trench should be backfilled with good clay that is thoroughly compacted by a heavy rubber tire or sheepsfoot roller. All dams should have a core trench!

Spillways should be constructed of adequate size and new, durable materials. Keep in mind that repairs on existing spillways can be very expensive and may require your pond to be emptied, so it’s best if the spillway lasts for a very long time. Also, if a spillway is not of adequate size or fails, your dam may become damaged or lost (both expensive to repair).

An appointment may be made with a technician to visit your site, where we will discuss the particulars of your site that will determine whether or not the site is physically and monetarily feasible for a pond. These particulars include:

Site Topography

How the lay-of-the-land lends itself to the placement and type of pond being considered.

Watershed

Whether the pond site will have enough watershed acres to supply the pond with the proper amount of water. Generally, a 1-acre pond should have 10–15 acres of watershed.

Soil Types

By looking up the soil types of the site in the Richland County Soil Survey, the technician will be able to determine if the soils mapped for the site have the characteristics needed to hold water and/or construct a dam.

If the site has been determined to be suitable to build a pond and the landowner wants to go to the next step, the District will schedule a Soil Scientist to personally look at the soils and give his professional opinion on the soil suitability for pond construction.

The District needs time to schedule an appointment with the Soil Scientist. Once we determine that he is needed, we will contact him and get a few dates that are available.

The landowner is responsible for supplying a backhoe that is capable of digging at least 2 feet below the deepest planned excavation. (Ex. If a pond is going to be 8 feet deep with a dam of 3 feet, then the pond area will have to be excavated 5 feet deep, the backhoe will then have to be able to dig a hole 7 feet deep to be 2 feet below the deepest excavation)

The holes must be dug while the District staff is present. It is important that the soil from the pit is seen as it comes out of the ground.