| Term No. | Term Name | Term Description |
| 948 | N-Year flood | A flood which has a probability of being equalled or exceeded once every N-years or has one chance in N of occurring in any one year...... |
| 7954 | N-Year flood | A flood that has a probability of being equalled or exceeded once in every N-years or has one chance in N of occuring in any one year...... |
| 6310 | Nadir | In remote sensing, point on the ground vertically beneath the perspective centre of the camera lens...... |
| 6853 | Nanoplankton | Floating, microscopic plant and animal life...... |
| 9337 | Nanoplankton | Phytoplankton whose lengths range from 10-50 µm...... |
| 2299 | Nappe | A sheet or curtain of water overflowing a weir, fall, etc. The nappe has an upper and a lower surface profile...... |
| 6524 | Narrow-base terrace | A terrace similar to a broad-base terrace in all respects excepting the width of ridge and channel...... |
| 2309 | Narrow-crested inclined weir | A weir formed by projecting an inclined wall (upstream or downstream) from the bed of the channel. Briefly, these are called `inclined weirs` (illustr..... |
| 7003 | Natality | The birth of offspring by a given animal population...... |
| 6613 | Native | An animal or plant that is indigenous to a given locale. ..... |
| 5583 | Natural aggregates | Naturally occurring aggregates that do not require crushing; washing and/or screening for grading may be necessary before use...... |
| 5485 | Natural bed (stone) | The surface of a stone whereon it was originally deposited, but not necessarily horizontal when resting in the quarry, the strata being often inclined..... |
| 2544 | Natural blanket | A cover of naturally occurring soil acting as a blanket. The natural blanket is generally less permeable...... |
| 5517 | Natural cement | The finely pulverized product resulting from the calcination of an argillaceous limestone at a temperature just sufficient to drive off the carbonic a..... |
| 7866 | Natural disaster | A serious disruption triggered by a natural hazard causing human, material, economic or environmental losses, which exceed the ability of those affect..... |
| 7793 | Natural drainage layout | A drainage system layout that follows natural depressions in the topography...... |
| 5126 | Natural drainage or Natural drainage capacity | The capacity of land to naturally remove excess water...... |
| 5050 | Natural drainage system | System of field drainage, passing through and connecting depressions...... |
| 5173 | Natural drainage systems, or Random drainage systems | Drains that follow the natural depression in the land, and converge like the frame of a tree (illustrated)...... |
| 6575 | Natural ecosystem | Ecosystem that attains its development without appreciable interference by man and is subject to natural forces of modification and destruction. ..... |
| 6599 | Natural environment | 1 - The atmospheric, geological and biological complex found in an area in the absence of artifacts or influences of a well-developed technological, h..... |
| 6464 | Natural erosion | Wearing away of earth`s surface by water, ice or other natural agents under natural environmental conditions, undisturbed by man. Synonymous with `geo..... |
| 7675 | Natural fertility | The nutrient status of soil that allows it to support plant growth, existing before any modification by humans...... |
| 4119 | Natural floodplain | Floodplain undisturbed by human interference...... |
| 7867 | Natural hazards | Natural processes or phenomena occurring in the biosphere that may constitute a damaging event. Natural hazards can be classified by origin namely: ge..... |
