Most of the existing rubber dams are of air filled types. Water filled rubber dams are not preferred for the following reasons:

(i) By giving the same sheet length and dam height, the tensile stress for water-filled dams is higher than that of air-filled rubber dams.

(ii) A significant size of water pond is normally provided for water-filled water dams for filling the rubber dams during the rising operation of dams.

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 advantages of rubber dams are as follows:

(i) Since rubber is flexible in nature it is capable of performing deflation even in the presence of dirt and sedimentation on the downstream side. However, for rigid steel-gate dams, it may not be possible to open when there is excessive sediment.

(ii) Since the foundation of rubber dams is comparatively lighter than that of steel-gate dams, it saves both construction cost and time.

(iii) Rubber dams can be designed with longer spans without piers while steel-gate dams require intermediate piers for long spans.

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.

Flow velocity at outlets is usually high. Without proper control of this energy, the subsequent bank erosion may result in failure of the banks. Therefore, some energy dissipating structures are designed to cope with this problem. Impact energy dissipaters may be provided at outlets by making use of impact walls to dissipate energy. Alternatively, the flows at outlet are dispersed artificially to achieve a significant loss of energy. However, the problem of cavitation may occur in this type of energy dissipating structures.

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.

Gabion aprons are provided at gabion walls to protect its toe from scouring due to river flow. The scouring would eventually lead to undermining of the gabion structure and affects its structural stability. The length of gabion apron should be long enough such that it reaches beyond the limit where scouring may form. A layer of getextile filter is normally placed at the base of gabion structures to prevent leaching out of foundation soils.

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.

In the design of access ramps, the direction is normally specified to be sloping down towards downstream so as to avoid the occurrence of over-shooting of flowing water for supercritical flow in case of aligning the ramps in the reverse direction of channel flow.

Note: Access ramps refer to ramps used for maintenance vehicles during routine maintenance of channels.

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.