In hydraulic engineering, a gravity weir is one that resists water pressure and uplift through its own weight. A non-gravity weir, conversely, is a structure where the stability against uplift is provided by additional components, such as the weight of divide piers or reinforced concrete foundations, rather than the mass of the weir body alone. The provided answer is consistent with this engineering definition.

The 20-40 rule is a specific empirical guideline used in agricultural engineering for determining the appropriate spacing and configuration of tile joints in drainage systems. It helps in maintaining hydraulic efficiency by ensuring that the joint spacing S is optimized relative to the pipe diameter and flow requirements, preventing sediment entry while allowing water infiltration.

A modular outlet, also known as a rigid module, is designed to deliver a fixed discharge that remains independent of the water level variations in the supply channel. This ensures a consistent water supply to the field, provided the water level in the distributary remains within a specified working range.

Drip irrigation delivers water directly to the root zone through emitters. For closely spaced crops, the number of emitters required becomes economically unfeasible and technically complex to install and maintain. Therefore, it is generally considered impractical for crops with high planting densities compared to widely spaced horticultural crops.

Annual intensity of irrigation represents the ratio of the total area irrigated during a single year to the total culturable commanded area. It is expressed as a percentage and serves as a key indicator for assessing the efficiency and utilization of irrigation infrastructure within a specific command area.

The discharge capacity of an irrigation channel is primarily governed by its cross-sectional dimensions, such as width and depth, along with the hydraulic gradient. While silt and slope influence the design to prevent erosion or sedimentation, the physical dimensions are the fundamental parameters defining the volume of water the channel can convey.

A fish ladder, also known as a fishway, is a hydraulic structure designed to allow fish to bypass obstacles like dams, weirs, or barrages. By creating a series of low steps or pools, it enables fish to swim upstream or downstream, ensuring that natural migration patterns are maintained despite the presence of man-made water control structures.

Broad irrigation, also known as sewage farming, is a method where raw or partially treated sewage is applied over large areas of land. The soil acts as a natural filter, removing pollutants while providing nutrients and water to crops. This practice requires careful management to prevent soil contamination and health risks associated with pathogens.

Pakistan possesses one of the world's largest contiguous irrigation systems. The canal network, which is vital for sustaining the country's agricultural productivity, spans approximately 64,000 kilometers. This extensive infrastructure facilitates the distribution of water from the Indus River system to millions of hectares of farmland, supporting the nation's food security and economic stability.

A virgin river, often referred to in certain hydrological contexts as an inland or terminal river, is one that does not reach the ocean. Its flow is entirely consumed by natural processes such as high rates of evaporation in arid regions or deep infiltration into the soil, preventing it from contributing to a larger river system or the sea.