Q. Design features of major bridge?
Important design features of major bridge projects should be tested and finalised by hydraulic model studies. Bridge waterway, shape, length and layout of guide bunds, along the bridge and approach banks, distribution of discharge in various spans of the bridge, additional training works required if any are such aspects which are normally studied in a hydraulic model.
Preliminary report of the bridge project.
Survey data
(i) Plan of the river extending over 2 meanders upstream and one meander downstream of bridge site. In case of a straight reach length of river reach may be at least 4 times the khadir width on upstream and 2 times on downstream. Tentative bridge location, guide bund layout, approach banks, marginal embankments, existing training works if any etc. should be shown on this plan. Edges of low water channels should be marked.
(ii) Cross sections on bridge line, at upstream, down stream· boundaries and in the intermediate reaches. Spacing of sections should be such that in the model, distance in between them would not be more than about 3 m.
Positions of sections and their zero chainages should be shown on the plan. The levels should be close enough to enable demarcating deep and shallow portions of the channels but can be wide apart where variations in levels are gradual. Cross section at bridge alignment should be observed at low water, medium flood and at near high flood stage.
(iii) Longitudinal section of the major channel along deep portion, termed Thalweg, Position of L section line should be shown on the plan giving periodical changes.