A detention pond spends most of its life looking like a low, empty meadow. That is what it is supposed to look like. Its work happens for a few hours after a storm, and everything about its shape is built around those hours.
At the heart of the pond is the principal outlet — usually a riser with a low-flow orifice, one or more intermediate openings, and a weir at the top. Each opening controls a different design storm. The orifice releases the small, frequent rainfall slowly. The weir passes the large storm. Together they hold the release rate at or below what the site produced before it was developed.
If the outlet clogs or the storm exceeds the design event, water leaves through a broad, armored spillway cut into the embankment. It is set above the design water surface and below the top of the berm, so the pond overtops in a controlled place rather than eroding the dam.
Embankments are constructed in compacted lifts of suitable material, with side slopes flat enough to mow and stabilize. A riprap or vegetated berm face resists the scour of concentrated flow at the outfall.
A small cell at the inlet slows incoming flow and drops out coarse sediment where it can actually be excavated later, instead of spreading it across the whole basin floor.
Mow the slopes, keep the trash rack clear, remove accumulated sediment from the forebay, and inspect after major storms. A pond that is never maintained gradually stops being a pond.