(SEM-VII) THEORY EXAMINATION 2019-20 WATER RESOURCES

WATER RESOURCES (RCE-702)

B.Tech – Semester VII

SECTION A

(Attempt all questions)

(a) Delta of a crop

Delta of a crop is defined as the total depth of water required by a crop during its entire base period. It represents the cumulative quantity of water supplied to the crop in the form of irrigation. Delta depends on factors such as crop type, climatic conditions, base period, and duty of water. It is an important parameter used in irrigation planning and canal design to ensure adequate water supply for crops.

(b) Advantages of furrow irrigation

Furrow irrigation is a surface irrigation method in which water flows through small channels between crop rows. This method is advantageous because it reduces water contact with plant stems, minimizing crop damage and disease. It allows better control of water application, reduces evaporation losses compared to flooding, and is suitable for row crops like sugarcane, cotton, and maize. Furrow irrigation also helps in efficient utilization of water on sloping land.

(c) Berms

Berms are horizontal or nearly horizontal strips of land provided between embankments, canals, or slopes. In water resources engineering, berms are used to improve stability, reduce erosion, and provide access for inspection and maintenance. They also act as safety features by reducing the velocity of flowing water and preventing slope failure.

(d) Recurrence interval of a storm using station year method

The recurrence interval, also known as return period, is the average time interval between occurrences of a storm of given magnitude. Using the station year method, the recurrence interval is calculated by dividing the total number of station-years of record by the total number of occurrences of the storm. This method is commonly used in hydrological analysis to estimate the probability of extreme rainfall events.

(e) Functions of headworks

Headworks are hydraulic structures constructed across rivers to divert water into canals. Their main function is to raise the water level, regulate flow, control sediment entry into canals, and ensure a continuous and controlled supply of water for irrigation and other purposes. Headworks also help in flood control and protection of canal systems.

(f) Conditions for selection of site for diversion headworks

The site for diversion headworks should have stable river banks, firm foundation strata, and a straight river reach. Adequate water availability, minimum sediment load, and easy approach to the canal alignment are important considerations. The site should also be safe from excessive flooding and economical for construction and maintenance.

(g) Ogee spillway

An ogee spillway is a type of overflow spillway commonly used in dams. Its crest profile resembles the shape of the lower nappe of water flowing over a sharp-crested weir. This shape allows smooth flow of water with minimal energy loss and reduces the risk of cavitation. Ogee spillways are efficient and widely used in concrete dams.

SECTION B

(Attempt any three)

(a) Average depth of annual precipitation using isohyetal method

The isohyetal method is one of the most accurate techniques for estimating average rainfall over a catchment. In this method, contours of equal rainfall called isohyets are drawn on a map. The areas between successive isohyets are measured, and the average rainfall for each strip is calculated. The weighted average rainfall over the basin is then obtained by considering the area-weighted contribution of each strip. This method accounts for spatial variation of rainfall and is widely used in hydrological studies.

(b) Rain gauge network and its importance

A rain gauge network consists of a number of rain-measuring stations distributed over a catchment area. Proper spacing and distribution of rain gauges ensure accurate measurement of rainfall. An efficient rain gauge network is essential for flood forecasting, water resource planning, and design of hydraulic structures such as dams, spillways, and drainage systems.

(c) Runoff and factors affecting runoff

Runoff is the portion of precipitation that flows over the land surface and through channels to rivers and reservoirs. It is influenced by factors such as rainfall intensity, soil type, land slope, vegetation cover, and catchment characteristics. Understanding runoff behavior is crucial for flood control, reservoir design, and watershed management.

SECTION C

(Attempt any one)

4(a) Design of non-alluvial channel using Bazin’s formula

The design of a non-alluvial channel involves determining channel dimensions that can safely carry the given discharge without erosion or deposition. Bazin’s formula is used to estimate flow velocity based on channel roughness and hydraulic radius. By assuming suitable values of depth, width, and side slopes, the channel section is designed to satisfy continuity and velocity requirements. Proper channel design ensures stability and efficient conveyance of water.

5(a) Typical barrage – plan and cross-section

A barrage is a low-head diversion structure constructed across a river to regulate water flow. A typical barrage consists of weir bays, under-sluices, canal head regulator, fish ladder, and energy dissipation arrangements. The plan shows the alignment and layout of these components, while the cross-section illustrates the structural details. Barrages are used to divert water into canals while allowing excess floodwater to pass safely.

6(a) Siphon aqueduct

A siphon aqueduct is a cross-drainage structure used when a canal passes below a natural drainage channel. In this structure, canal water flows under pressure through barrels below the drain bed. Siphon aqueducts are used when sufficient headroom is not available for an aqueduct. Hydraulic design ensures safe flow without excessive head loss.

7(a) Phreatic line in earthen dams

The phreatic line represents the upper boundary of seepage flow through an earthen dam. It separates the saturated and unsaturated zones. Determination of the phreatic line is essential for analyzing seepage, stability, and safety of earthen dams. Methods such as flow nets and Casagrande’s method are commonly used to locate the phreatic line accurately.