(SEM VI) THEORY EXAMINATION 2021-22 RIVER ENGINEERING

RIVER ENGINEERING (KCE062)

Section-wise Detailed Answers – B.Tech Semester VI

SECTION A

(Attempt all questions – brief but conceptually complete explanations)

Q1(a) Sediment transportation

Sediment transportation in rivers refers to the movement of soil particles such as sand, silt, gravel, and clay by flowing water. The capacity of a river to transport sediment depends on velocity, discharge, slope, and sediment size. Sediments are carried in different forms such as bed load, suspended load, and wash load. Sediment transport plays a major role in shaping river channels and influencing erosion and deposition processes.

Q1(b) Methods of river classification

Rivers can be classified based on their origin, geological formation, discharge variability, sediment characteristics, and channel pattern. Common classifications include perennial and non-perennial rivers, alluvial and non-alluvial rivers, meandering, braided, and straight rivers.

Q1(c) Protection of rivers from erosion

Rivers are protected from erosion by constructing river training works such as spurs, groynes, guide banks, levees, and revetments. Vegetative measures and bio-engineering techniques are also used to stabilize riverbanks. These methods reduce flow velocity near banks and prevent excessive scouring.

Q1(d) Meander length and sinuosity

Meander length is the distance measured along the centerline of the river between two successive crests or troughs of a meander. Sinuosity is the ratio of the actual river length to the straight-line distance between two points. A sinuosity greater than one indicates a meandering river.

Q1(e) Purpose of a groyne

A groyne is a transverse river training structure constructed from the riverbank into the river. Its purpose is to deflect the flow away from the bank, reduce erosion, encourage sediment deposition, and stabilize the channel alignment.

Q1(f) Alluvial river

An alluvial river is a river that flows through loose sediments such as sand, silt, and gravel deposited by the river itself. Its bed and banks are continuously reshaped due to erosion and deposition. Most Indian rivers fall under this category.

Q1(g) Methods of river classification

Rivers may be classified based on hydrology, sediment load, geomorphology, flow regime, and planform geometry. Each classification helps engineers understand river behavior and design suitable control measures.

Q1(h) Time series

A time series is a sequence of data points recorded at successive time intervals. In river engineering, time series data such as discharge, rainfall, sediment load, and water level are used for flood forecasting, trend analysis, and river behavior prediction.

Q1(i) Permeable and impermeable spurs

Permeable spurs allow water to pass through them while reducing velocity, whereas impermeable spurs completely block flow. Permeable spurs promote gradual sediment deposition, while impermeable spurs provide stronger protection against erosion.

Q1(j) Marginal bund and guide bund

A marginal bund is constructed parallel to the river to protect adjacent land from flooding. A guide bund is constructed near hydraulic structures like bridges to guide the river flow safely through the structure and prevent erosion.

SECTION B

(Attempt any three – detailed explanations)

Q2(a) Meandering and its causes

Meandering is the natural tendency of rivers to form winding curves along their course. It occurs due to non-uniform velocity distribution across the channel, sediment transport, bank erosion on the outer bends, and deposition on inner bends. Factors such as low slope, fine sediment, and high discharge variability promote meandering.

Q2(b) Parameters responsible for river instability

River instability arises due to changes in discharge, sediment load, channel slope, bank material, and human interventions such as dams and embankments. Excess sediment causes aggradation, while sediment deficiency leads to degradation. Variations in flow regime disturb the equilibrium of the river.

Q2(c) Influence of stream restoration on social and cultural environment

Stream restoration improves water quality, reduces flood risk, and enhances ecological balance. It positively impacts local communities by improving livelihoods, recreational opportunities, and cultural connections with rivers. Restored rivers often revive traditional practices and promote sustainable development.

Q2(d) Use of levees for protecting cities from floods

Levees are raised embankments constructed along riverbanks to prevent floodwaters from entering urban areas. They confine the river within a defined channel, increasing flood protection. Proper design and maintenance of levees are essential to avoid catastrophic failure.

Q2(e) Uses and features of guide banks

Guide banks are used to confine river flow near bridges and barrages. They prevent erosion of abutments and foundations. Salient features include curved alignment, adequate freeboard, pitching protection, and smooth transition with the natural river channel.

SECTION C

Q3(a) Flashy vs virgin rivers and aggrading vs degrading rivers

Flashy rivers experience sudden rise and fall in discharge due to intense rainfall and steep slopes, while virgin rivers remain undisturbed by human activity. Aggrading rivers deposit sediments raising bed levels, whereas degrading rivers experience erosion and bed lowering due to excess flow energy.

Q3(b) River morphology and Rosgen classification

River morphology deals with the shape, size, pattern, and behavior of river channels. The Rosgen classification system categorizes rivers based on channel slope, sinuosity, width-depth ratio, and bed material. It helps in river assessment, management, and restoration planning.

Q4(a) Bed load, suspended load, and wash load with saltation

Bed load consists of coarse particles moving along the riverbed by rolling and sliding. Suspended load remains suspended in water due to turbulence, while wash load consists of fine particles carried in suspension. Saltation is a process where bed load particles move in short hops due to lifting and settling forces.

Q4(b) Delta formation and control measures

Deltas form when sediment-laden rivers enter a still body of water, causing deposition due to reduced velocity. Continuous sediment accumulation leads to delta growth. Control measures include dredging, sediment flushing, river training, and upstream sediment management.

Q5(a) Bed forms in alluvial channels

Alluvial channels exhibit bed forms such as ripples, dunes, plane beds, and antidunes depending on flow velocity and sediment size. These bed forms influence resistance to flow and sediment transport.

Q5(b) River restoration and types of restoration works

River restoration aims to restore natural river functions and ecological balance. Types of restoration include channel re-meandering, bank stabilization, floodplain reconnection, and habitat enhancement.

Q6(a) Discharge measurement techniques in rivers

Discharge measurement techniques include velocity-area method, float method, current meter method, and indirect methods such as slope-area method. Modern techniques include acoustic Doppler current profilers.

Q6(b) Bio-engineering techniques

Bio-engineering techniques combine vegetation with engineering structures to stabilize riverbanks. Methods such as live staking and brush layering reduce erosion while enhancing environmental sustainability.

Q7(a) Relationship between discharge, geometry, and velocity

This relationship is described by hydraulic geometry, which explains how channel width, depth, and velocity vary with discharge. Channel bed roughness decreases downstream due to finer sediment and smoother bed forms.

Q7(b) Objectives and types of river training works

River training works aim to control river flow, prevent erosion, protect structures, and improve navigation. Types include guide banks, groynes, spurs, levees, and revetments.