According to one aspect of the invention, an inlet of an underground reservoir having a multiple-stage structure includes: a flow portion, wherein water flowing in the flow portions; a drop portion transporting the water to a underground reservoir from the flow portion; and an inlet portion having a multiple-stage structure to generate a vortex in the water to be transported to the drop portion.

A vortex flow control device (2) comprises a chamber (20), having a first end (21), a second end (22), an inlet (23) proximal to and/or at the first end (21) and an outlet (24) proximal to and/or at the second end (22), wherein the first end (21) and the second end (22) are mutually opposed and wherein the inlet (23) and the outlet (24) are mutually orthogonal; wherein the chamber (20) defines a first cylindrical volume CV1 proximal to and/or at the first end (21) and wherein the inlet (23) is tangential to the first cylindrical volume CV1; and wherein the chamber (20) defines a tapered volume TV disposed between the first cylindrical volume CV1 and the outlet (24).

A drainage device is provided. The device includes a novel floating surface drain or skimmer to manage draining of liquid, such as draining of water from stormwater impoundment ponds or structures.

A water containment system has: a peripheral dam formed of one or more arcuate longitudinal wall sections that are configured to be secured in an assembled position in use around a water tank as the water tank rests on a ground surface, the peripheral dam defining an open water-tank-receiving base; and a drain port defined in the peripheral dam. In a method of retrofitting a water containment system around a water tank, the method includes: assembling a peripheral dam, formed of one or more arcuate longitudinal wall sections around the water tank as the water tanks rests on a ground surface; securing the peripheral dam to the ground surface; and connecting a drain line from a drain port in the peripheral dam to a drain.