The 3rd Northern Forum FWG Meeting:
Problems of Ice Jams and Biggest Flood on Rivers of Yakutia
By D.Nogovitsyn,
North Physical Technical Problems Institute
Siberian Branch, Russian Academy of Sciences
1. On Lena River ice jams are formed, as a rule, in the same places as the centers of ice jam formation spreading over large river areas. Some thick ice jams formed between water measurement stations have been missed observing water levels. Usually ice jam formation beyond observation area is fixed by airborne prospecting, 20 years of the latter having been providing for the scheme of ice jam formation centers on Lena River (see Fig.2). The map shows that ice jams form on Lena River entire flow. The most unsafe are the river portions adjacent to inhabited localities.
2. There seem to be no regular patterns in ice jam thickness and recurrence, as these depend on spring tide formation features. Long springs lead to interruptions in tide formation and relatively low water levels during the river opening, thus causing formation of more ice jams of low intensity. In short springs tides are formed intensively, with less ice jams; however, resulting water level increase reaches extreme height.
The analysis made for the characteristics of ice phenomena in every water measurement station for 50-60 years of observations have revealed the following cases of ice jams in observation points: Tabaga — 7, Yakutsk — 12, Kangalassy — 10.
3. Excess of the observed levels over critical (i.e. marks over which several buildings and lands are flooded) has been also observed for 50-60 years. The number of such cases was 21: Tabaga (1938-1999, 2001 n=61), Yakutsk (1942-1992, 2001 n=49), Kangalassy (1936-1992, 2001 n=57).
For the most part high levels were observed at ice jams, and in some years also during ice drift.
On Lena River ice jam formation depends on neither spring ice thickness nor water level in the beginning of freezing-over.
4. High probability of an ice jam formation is related to the moment when the river opening and consequent ice drift coincide with sharp decrease of outdoor temperature. Thus, ice jam formation forecasting is closely connected to ice shearing, ice drift, and sharp decrease of outdoor temperature forecast in the period.
High freezing-over autumn level and relatively thick ice in winter affect mainly the formation of high (over critical) levels in spring when ice jams are already formed.
5. As evidenced by the foregoing, the most important problems of ice jam formation on mid-Lena River include:
- more detailed characteristics of ice cove distribution over river portions,
- studies of temperature conditions influencing ice jams and river breaking up,
- higher reliable and preliminary forecasting the spring tidal wave passage. |
