Glossary of Engineering & Biological Terms

Structural & Engineering Terms

Bathymetry

The measurement of depth of water in oceans, seas, or lakes. In pond construction, bathymetric modeling refers to mapping the 3D underwater topography, including varied depth zones, stepped terraces, and sloped floors.

EPDM (Ethylene Propylene Diene Monomer)

A highly flexible, synthetic rubber geomembrane used for pond lining. Aquatic-grade EPDM is safe for fish, highly resistant to UV degradation, and can elongate up to 300% without breaking, making it ideal for custom, hand-dug excavations.

Hydrostatic Pressure

The pressure exerted by a fluid at equilibrium due to the force of gravity. In pond construction, this refers to the immense outward and downward force exerted by thousands of gallons of water pressing against the liner and retaining walls. It also refers to groundwater pressing *upward* from beneath the liner, which can cause the liner to float if the pond is emptied.

Overhang / Anchor Trench

The extra linear footage of pond liner material that extends past the water's edge. This material is buried in a perimeter trench (anchor trench) and covered with boulders or soil to mechanically lock the liner in place and prevent the sheer weight of the water from dragging the sheet into the hole.

Total Dynamic Head (TDH)

The total equivalent height that a fluid is to be pumped, taking into account friction losses in the pipe. It is calculated by adding the static lift (vertical height) and the friction loss (resistance from pipes, elbows, and filters). It determines the true operating output (GPH) of a water pump.

Biological & Filtration Terms

Ammonia ($NH_3$)

A highly toxic chemical compound excreted primarily from the gills of fish as a byproduct of metabolizing protein. Even small trace amounts of ammonia can burn gill tissue and kill fish. It must be processed by the biological filter.

Biological Filtration

A filtration stage designed to harbor colonies of beneficial nitrifying bacteria. These bacteria consume toxic ammonia and nitrite, converting them into relatively harmless nitrates. This process is known as the Nitrogen Cycle.

Dwell Time

The amount of time water spends in contact with a specific filtration component. For example, water must pass through a UV clarifier slowly enough (high dwell time) to ensure single-celled algae are exposed to enough radiation to destroy their DNA.

Mechanical Filtration

The physical removal of solid waste (leaves, fish feces, uneaten food) from the water column. Devices like skimmers, sieves, and filter pads physically trap debris so it can be manually removed before it decomposes and releases ammonia.

Turnover Rate

The speed at which a pump circulates the entire volume of a pond through the filtration system. A 2-hour turnover rate means the pump circulates a volume equal to the entire pond every two hours.