The most effective arrangement for diverting excess storm water into a natural drainage, is

ANS:C - siphon spill way

A siphon spillway is a type of hydraulic structure used in water engineering to convey excess water over or through an obstacle, such as a dam or embankment, using the siphon effect. It is designed to allow water to flow from a higher elevation to a lower elevation, typically over or through a barrier. Here's how a siphon spillway generally works:

1. Structure Design: A siphon spillway consists of an inlet structure, often located near the top of the dam or embankment, where water enters the spillway. The spillway may include a vertical drop or conduit that connects the inlet structure to the outlet structure.
2. Siphon Effect: The key feature of a siphon spillway is the use of the siphon effect to draw water from a higher elevation to a lower elevation. This effect relies on the difference in water levels between the inlet and outlet sides of the spillway. When the water level on the inlet side is higher than the outlet side, gravity causes water to flow into the spillway, creating a siphon effect that draws water over or through the spillway.
3. Flow Control: The flow of water through the siphon spillway can be controlled using various mechanisms, such as gates or valves, to regulate the discharge rate and manage water levels in the reservoir or watercourse.
4. Discharge: As water flows through the spillway, it is conveyed over or through the obstacle, such as a dam or embankment, and discharged downstream into a natural drainage channel or watercourse.

Siphon spillways are often used in situations where traditional overflow weirs or channels are not feasible due to topographical constraints or environmental considerations. They provide an efficient and controlled means of managing excess water flow and preventing flooding while minimizing the impact on the surrounding landscape. Overall, siphon spillways are an important component of water management systems, particularly in dams, reservoirs, and irrigation projects, where effective drainage and flood control are essential.