| Term No. | Term Name | Term Description |
| 3847 | U-abutment | Form of abutment where the wing walls return at 90o...... |
| 4482 | U-Pump | A reciprocating piston pump wherein the valves are placed in the piston and the flow through the cylinder is in one direction with no reversal...... |
| 6717 | Ubiquitous | Plant or animal species capable of thriving under many environmental conditions...... |
| 2638 | Ultimate bearing capacity | The average load per unit of area required to produce failure by rupture of a supporting soil mass...... |
| 1778 | Ultimate pH | The pH after all diffusible anions and cations have been removed...... |
| 5538 | Ultra high-early strength cement | A cement that hardens more rapidly than ordinary Portland cement, because of its extraordinary particle fineness...... |
| 6265 | Ultrasonic velocity sensor, or Ultrasonic flowmeter | A microprocessor-based instrument that measures the velocity of flow at a certain depth by simultaneously transmitting ultrasonic pulses through the w..... |
| 9366 | Ultraviolet (UV)-B Radiation | Solar radiation within a wavelength range of 280–320 nm, the greater part of which is absorbed by stratospheric ozone. Enhanced UV-B radiation suppr..... |
| 1822 | Unavailable soil moisture, or Unavailable water | Soil moisture held so firmly by molecular forces that it cannot ordinarily be absorbed by plant roots with sufficient rapidity to produce growth...... |
| 4901 | Unavoidable farm losses | Principally those losses which are due to normal field evaporation and deep percolation...... |
| 4176 | Uncased well | A tubewell, such as in deep rock, with little or no casing. ..... |
| 8578 | Uncertainty | Outcomes resulting from each course of action that are not explicitly known and to which probabilities cannot be assigned...... |
| 1145 | Unconfined aquifer | An aquifer in which the groundwater table is free to rise and fall according to hydraulic gradients...... |
| 5285 | Unconfined water | Water that is free flowing...... |
| 1142 | Unconsolidated aquifer | An aquifer comprised mainly of gravels or other porous materials that may not be structurally stable when penetrated by a well bore...... |
| 2659 | Unconsolidated undrained test, or Quick test | A soil test when the time is not allowed for consolidation and the water content of the test specimen remains practically unchanged during the applica..... |
| 8951 | Uncontrolled mosaic | A mosaic in which the photographs have not been adjusted by reference to ground control...... |
| 2745 | Uncontrolled spillway, or Ungated spillway | A spillway the crest of which permits water to discharge, whenever the reservoir surface is higher than the crest...... |
| 5166 | Under inlet | Any device other than a well that admits groundwater to a drain pipe. In its usual form it consists of an opening filled with broken stone or gravel...... |
| 6677 | Under story | A layer of foliage below the level of the main tree canopy...... |
| 6439 | Undercut-slope bank | The inside bank of a meandering stream that is eroded by stream action...... |
| 7788 | Underdrainage | Removal of excess water from the soil by a subsurface system of drainage...... |
| 2423 | Underflow density currents | The density currents flowing under another fluid...... |
| 2428 | Underflow turbidity currents - plunging type | Flow of the turbid water into a reservoir plunging directly under the clear water in the lake. The formation is indicated by the collection of flowing..... |
| 2429 | Underflow turbidity currents - settling type | When the inflowing muddy water does not dive under the clear water but pushes it downstream and forms a considerable body of muddy water and the sedim..... |
