It is not uncommon that local flooding still occurs despite that drainage improvement measures have already been implemented in its vicinity. In some low-lying areas the ground level is lower than the water level in the nearby main drainage channel. As the channel collects stormwater from catchment by gravity, it is natural to follow that runoff from these low-lying areas can hardly be discharged into the channels during rainstorm. Such phenomenon is called “residual flooding”.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

Common structural approaches to combat flooding problem includes replacement/upgrading of drains, temporary flood storage with pumping facilities, cross catchment diversion and infiltration. The concept of infiltration involves the reduction of surface runoff so that the amount of overland flow is reduced. To enhance absorption of runoff into the ground, structures and facilities have to be designed and provided. For instance, porous pavement and infiltration pond could serve as infiltration facilities to cut off some surface runoff.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

Manholes are provided in locations where there are changes in size, direction and gradient of gravity pipelines. In normal practice for straight pipelines manholes have to be installed at a certain spacing to facilitate the maintenance of pipes. With the introduction of manholes, there are various reasons which account for the manhole loss:

(i) The sudden expansion of inflow into manholes and the sudden contraction of flow out of manholes lead to significant energy losses.

(ii) It is not uncommon that several pipes may be connected to the same manhole. As such, the intermixing of flow takes place inside the manhole and this leads to head losses.

(iii) Flow inside the manholes may be designed to change directions which contribute to additional losses.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

Cavitation refers to the formation of air bubbles in fluid in low-pressure condition which is lower than the saturation pressure. It is a potentially damaging condition in which the fluid in pipes or sewers is at high velocities. By Bernoulli’s Equation, at high flow velocities, the pressure head of fluid is reduced accordingly. As the fluid pressure is less than saturation pressure, dissolved gases are released from the fluid and these air bubbles will suddenly collapse when the flow enters into a region of higher pressure. This produces a high dynamic pressure which causes damage to the pipelines due to its high frequency.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

The use of hydraulic jump in hydraulic engineering is not uncommon and the creation of such jumps has several purposes:

(i) Its main aim is to perform as an energy-dissipating device to reduce the excess energy of water flows.

(ii) The jump generates significant disturbances in the form of eddies and reverse flow rollers to facilitate mixing of chemicals.

(iii) During the jump formation, considerable amount of air is entrained so that it helps in the aeration of streams which is polluted by bio-degradable wastes.

(iv) It enables efficient operation of flow measuring device like flumes.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.