Changes in the flooding regime of the Lena River left bank floodplain near Yakutsk

The flood protection of Yakutsk includes 75 km of dams, covering about 40% of the left-bank part of the valley bottom (270 km2). The dams reduced the width of flooding in the Yakutsk area by 1,3-5 km (by 15-30%). The construction of the protective perimeter is accompanied by the development of the floodplain and the transformation of its urochisches. Four types of basins have emerged on the floodplain. The first type is a regularly flooded riverbed zone. The flood flow transformation is local there; meadow and forest complexes of the floodplain are preserved. The second type includes the central floodplain areas, which have preserved the hydraulic connection with the riverbed. The probability of their flooding has decreased by 2-3 times. They dry out, their swamps and hydromorphic complexes degrade, meadows are being drained; pasture digression has increased, and the floodplain is actively being built up. The third type is isolated, dammed pools. Depending on the water balance, they undergo drying or water logging. In the residential area water logging prevails, which is facilitated by the disruption of the network of floodplain hollows blocked by dams. Lack of the flowing worsens the drainage of the floodplain: flooding of quarters is common; water accumulates under buildings, destroying piles and foundations, which lead to accidents. The fourth type includes the basins of small rivers flowing through the floodplain. Currently, their flooding is limitedly possible; drying contributes to the spread of dry and steppe meadows on the slopes of low ridges and into the bottoms of hollows. The pastoral use of the floodplain has led to the replacement of forest urochisches by meadow-shrub communities; however, the restoration of forests and woodlands takes place around new rural settlements. Non-flooded areas are being built up. During further development of the floodplain, not only water protection measures should be provided, but also environmental protection measures and measures to improve floodplain areas leaving the flooding zone.