Due to reasons for surplus amount of water to be present in canal, supplies shall be reduced or stopped from head works. Therefore in order to avoid this damage immediate action is needed. This can be achieved by means of an escape generally called surplus water escape.

In this type of escape crest of weir wall is kept at RL equal to canal FSL. When water level rises up FSL it gets escaped.

The discharge value of water has to be adjusted to any value necessary to distribute water effectively. This is done with help of regulators.

When difference between two stilling wells is h, n discharge is given by formula \(Q = C_d(a_1 * a_2 / \sqrt{(a_1^2 ? a_2^2)})\sqrt{2gh}\) where, C_d = 0.95 to 1, a₁ = area at entrance, and a₂ = area at throat.

The conditions are considered for worst conditions of flow. The flow of canal should be taken as it is when re is full supply of discharge down channel with all gates of both head and cross regulators fully open. The discharge in main channel is low but in off take channel is running full, FSL is maintained by partial opening of gates of cross regulator.

If difference in water level of distributary and water course is known n by using formula total loss of head = entry loss + frictional loss + velocity head at exit. Mamatically it is represented as H_L = 0.5V²/2g (1.5 + f? l/d) where l = length of pipe, d = diameter of pipe and f? = coefficient of friction.

It is a modular outlet with costly and complicated arrangements. It is based on free vortex flow and holds good for standard design in which outlet index = 2 and H/D = 1/7 where H is head at outer circumference and D is difference of level measured from minimum water level in parent channel to floor of eddy chamber.

The outlet or module should be simple because it can easily be constructed or fabricated by masons or technicians. Interference with cultivators should also be avoided to prevent undue tapping of water by cultivators.

An upward rotational flow is imparted if head causing flow increases at outer wall restricting against baffles. The water spins round in compartment between two successive baffles and finally drops on incoming water stream of water. This dissipates excess energy and helps in maintaining constant discharge for a wide variation in head.

The discharge through free pipe outlet and Kennedy?s flume outlet is given by-
Q = C_d. A. (2gH)^1/2 where H is head on U/s side measured from FSL of distributary up to centre of pipe outlet, C_d is coefficient of discharge, and A is area of cross-section of pipe.
The discharge through an open flume outlet is given as: Q = C_d. W H^3/2 where W is width of throat.
The discharge through AOSM is given by- Q = C_d. (W. y₀).(2gH)^1/2 where ?y₀? is height of an orifice opening.