(SEM-VIN) THEORY EXAMINATION 2018-19 WATER RESOURCES ENGINEERING

SECTION A

Attempt all questions in brief (2 × 10 = 20 marks)

(a) What is meant by Border Flooding?

Border flooding is a surface irrigation method in which the field is divided into long, narrow strips called borders. These strips are separated by small earthen ridges. Water is supplied at the upper end of the border and allowed to flow slowly down the length under gravity. This method is suitable for crops like wheat and sugarcane and is commonly used where land slope is uniform.

(b) Define Intensity of Irrigation.

Intensity of irrigation is the percentage of the gross cultivated area that is irrigated annually. It indicates how intensively irrigation facilities are being used. A higher intensity of irrigation means better utilization of water resources and irrigation infrastructure.

(c) Explain Lacey’s silt factor.

Lacey’s silt factor is a parameter used in the design of stable alluvial channels. It represents the effect of silt size on channel characteristics. It depends on the mean particle size of the bed material and helps in determining channel dimensions such as width and depth to ensure stable flow without erosion or silting.

(d) Define Leaching.

Leaching is the process of removing excess salts from the soil by applying sufficient irrigation water. The water dissolves the salts and carries them downward beyond the root zone. Leaching is important in areas where soil salinity affects crop growth.

(e) What is meant by “Cross-Drainage Works”?

Cross-drainage works are structures constructed where a canal crosses a natural drainage channel such as a river or stream. These works allow both canal water and drainage water to cross each other safely without interference. Examples include aqueducts, siphon aqueducts, and super passages.

(f) Define Time factor and Capacity factor.

Time factor is the ratio of the time a canal actually runs to the total time for which it was designed to run. Capacity factor is the ratio of the mean discharge to the designed full supply discharge of the canal. Both factors help in evaluating the performance of irrigation systems.

(g) Explain Base period and Crop period.

Base period is the time between the first watering of a crop and the last watering before harvesting. Crop period is the total time from sowing to harvesting. Base period is always slightly less than the crop period.

(h) What is duty of water?

Duty of water is the area of land that can be irrigated by a unit discharge of water flowing continuously during the base period. It is expressed in hectares per cumec and depends on crop type, climate, and soil conditions.

(i) What is delta of a crop?

Delta of a crop is the total depth of water required by a crop during its entire base period. It includes water used for evapotranspiration and losses. It is usually expressed in centimeters.

(j) Define irrigation efficiency.

Irrigation efficiency is the ratio of the water effectively used by crops to the total water supplied from the source. It indicates how efficiently water is being used in irrigation practices.

SECTION B

Attempt any one part (10 × 1 = 10 marks)

Explain different methods of irrigation.

Irrigation methods are broadly classified into surface irrigation, subsurface irrigation, sprinkler irrigation, and drip irrigation.

Surface irrigation is the most traditional method where water flows over the soil surface by gravity. Examples include border flooding, basin irrigation, and furrow irrigation. This method is simple and economical but has higher water losses.

Subsurface irrigation involves supplying water below the ground surface directly to the root zone. It reduces evaporation losses but requires proper soil conditions and maintenance.

Sprinkler irrigation simulates rainfall by spraying water through nozzles under pressure. It is suitable for uneven land and sandy soils. Water distribution is uniform, but installation and energy costs are high.

Drip irrigation supplies water drop by drop directly near the plant roots. It is the most efficient method, conserving water and improving crop yield. However, it has high initial cost and requires skilled operation.

SECTION C

(a) Distinguish between flow irrigation and lift irrigation.

Flow irrigation is the method in which water flows naturally from a river, canal, or reservoir to the fields under gravity. It does not require pumping and is economical for large-scale irrigation. Lift irrigation, on the other hand, involves lifting water using pumps from a lower level source such as a river or well to irrigate higher land. Lift irrigation requires energy and is costlier but useful where gravity flow is not possible.

(b) Numerical: Capacity of Reservoir

Using the given table of crops, base periods, duties, and areas, the total water requirement for each crop is calculated using the duty–delta relationship. The total demand is adjusted by considering conveyance losses of 26% and reservoir losses of 10%. After accounting for these losses, the required capacity of the reservoir is calculated in hectare-meters.

(This numerical is solved step-by-step in exams using standard duty-delta formulas and loss adjustments.)