The discharge capacity of an irrigation channel is fundamentally determined by its physical dimensions, specifically the cross-sectional area, the wetted perimeter, and the hydraulic radius, in conjunction with the channel slope and roughness coefficient (Manning's or Chezy's). While silt and sediment affect stability, the actual volume of water a channel can transport is governed by its hydraulic geometry.

Retrogression refers to the degradation of the riverbed downstream of a hydraulic structure like a weir. This occurs because the structure traps sediment, causing the water released downstream to be 'hungry' or sediment-deficient, which leads to increased scouring and erosion of the riverbed material.

A deltaic river is characterized by the formation of a delta at its mouth. As the river approaches the sea, its velocity decreases, causing it to deposit its sediment load. This deposition forces the river to split into a network of smaller channels, known as distributaries, which create a distinct landform known as a delta.

Direct runoff is defined as the part of the runoff that enters the stream immediately after rainfall or snowmelt. It includes surface runoff, prompt interflow (sub-surface runoff), and channel precipitation. Note: The provided answer C is technically incomplete as it includes deep percolation, which is usually a loss.

Khosla's theory is the standard method used in hydraulic engineering to calculate the pressure distribution and the required length of the impervious floor (apron) downstream of hydraulic structures like weirs and barrages. It improved upon earlier concepts by providing a more accurate mathematical approach to prevent piping and undermining of the structure's foundation by seepage water.

Tanda Dam is a small multi-purpose dam located in the Kohat District of Khyber Pakhtunkhwa, Pakistan. It is constructed on the Kohat Toi river, which is a tributary of the Indus River system. The dam serves as a vital water reservoir for irrigation and local water supply needs in the surrounding region.

In a radial centrifugal pump, the inlet angle is designed such that the relative velocity vector is directed radially to minimize shock losses as the fluid enters the impeller vanes from the suction pipe.

River training works encompass various engineering interventions, such as guide banks, spurs, and embankments, designed to stabilize the river channel. These works aim to guide the flow in a desired direction, prevent bank erosion, and ensure that water approaches hydraulic structures like weirs or bridges in a controlled and predictable manner.

The base period represents the duration from the first irrigation to the final watering before harvest. Using the irrigation engineering formula B = (Delta * Duty) / 8.64, where Delta is 0.5 meters and Duty is 1200 hectares/cumec, the calculation yields B = (0.5 * 1200) / 8.64, which equals approximately 69.44 days, rounding to 70 days.

Irrigation intensity refers to the proportion of the total cultivable command area that is actually irrigated by a specific flow rate, such as one cusec, during a season. This metric is vital for irrigation engineers and planners to assess the efficiency of water distribution systems and to ensure that water resources are allocated effectively across the agricultural landscape.