Critical levels of the summer season in the mouth areas of the rivers of the Ob-Taz region

Abstract

Situations in which water levels in summer fall below design (critical) marks for at least 10 days are considered dangerous phenomena. In such situations, navigation is hampered or stopped, resulting in significant economic damage. As our previous studies have shown, the mouth areas of the rivers of the Ob-Taz region that are used for navigation are prone to these dangerous phenomena. The aim of this work is to analyze the duration of the water level standing below the design marks and to estimate its characteristics for the navigation period at the posts Salekhard, Aksarka, Nyda, Nadym, Samburg, Sidorovsk, Tasovsky, Nahodka over an extended series of observations. Of the posts listed, the analysis has not previously covered Aksarka and Nadym data. Project levels have changed for some of the posts over the years, requiring updated estimates. The analysis was carried out on the basis of average daily levels at the posts for the period 1936-2013 published in the annual edition of the Water cadastre. If necessary, information on the water flow was included. Unfortunately, the quality of the data for most of the posts except Salekhard is not satisfactory due to numerous passes. The technique consists in the analysis of continuous level standing relative to the design values by specified intervals of duration. The results show that all the posts experienced levels lower than the design marks. In Nahodka it happened annually, in Nadym, Samburg, Sidorovsk — in 75.6 %, 68.3 %, 54.2 % of all the years of observations, respectively. Of all the cases of standing levels below the design mark, those of continuous standing with a dangerous duration were observed in Sidorovsk 71 %, Nadym 67.3 %, Samburg 41.1 %, Nahodka 40.0 %, Aksarka 26.1 %, Nyda 19.1 %, Salekhard 16.7 %. Only in Tasovsky were there no cases of dangerous duration. The largest number of years with dangerous cases fall on the 10-th anniversary of 1981-1990. In individual navigation seasons, two to four cases of continuous standing levels of dangerous duration were observed. At the same time, minimum average daily levels fell below critical values by a value from 189 cm (Nahodka) to 53 cm (Samburg). The maximum number of days with cases of dangerous duration in one season was in shares from the period of open channel from 91.4 % (Nahodka) to 36.6 % (Salekhard). The sum of days with levels below the design values for the season depends inversely on the amount of river flow.