SPECIFIC FEATURES OF WATER BALANCE AND DISTRIBUTION OF WATER RUNOFF AND NANOSE IN THE PARANA DELTA

The current values of the components of the water balance of the Parana Delta, one of the largest deltas of South America, as well as the results of calculations of the actual distribution and redistribution of water runoff and sediment yield in the delta branches are presented. The climatic features of the delta's water balance are revealed. Long-term changes in the water flow distribution in the delta branches are considered and estimates of the dynamics of delta estuarine line are given.

ПРОЯВ КРАЙОВОГО ЕФЕКТУ В СТРУКТУРІ ЗАРОСТЕЙ МАКРОФІТІВ ПРИ ЗМІНІ ГІДРОЛОГІЧНОГО РЕЖИМУ

This paper considers the changes in the structural characteristics and macrophyte underwood species diversity of the Kiliya Danube Delta as a detection of the edge effect when the environmental conditions are changing. A total of 27 species of water vascular plants were identified. Moreover, filamentous algae were found but their species and genus were not determined. Biodiversity changes were evaluated using the Shannon Index which integrates species richness and their uniformity in the group. The significance of the results was assessed by testing the null hypothesis which is to verify the absence of changes in the average values of the sample using the Student's t test. Transitional watercourses (channels) have the highest indicators of information diversity where the manifestation of the edge effect is more distinct. There were statistically significant differences between the Shannon index in the end of the branch and the channel, as well as between the channel and the beginning of the water body, at the level of p = 0.05 which indicates the strength of the edge effect in the sample. It is established that the edge effect is reliably displayed in the transition from lotic (delta branches) to lentic conditions (non-flowing reservoirs – "corners"). It is displayed in the form of increasing biological diversity, decreasing in the role of monodominant groups and also in increasing floating pleistophytes quantity. Also in the channels which connect a flowing stream and waterbody is the highest species diversity and the highest Shannon index. Under lotic conditions even in the places of branch ramification and at different distances from such branches, the manifestation of the edge effect is not statistically proven. Therefore, we cannot prove the existence of edge effect in these objects despite the fact that we observe a tendency to increase species diversity at the beginning and end of the watercourse. The ecological structure of macrophyte groups is practically unchanged within each individual watercourse along its entire length. The Ochakivsky branch is dominated by groups of high-grass helophytes and floating pleistophytes, in Starostambulsky by groups of high-grass helophytes and rooted gidatophytes, and in the Vodtochny by low-grass gelophytes and floating pleistophytes.

Geospatial Analyses for Assessing the Driving Forces of Land Use/Land Cover Dynamics Around the Nile Delta Branches, Egypt

Major driving forces can alter Land use/Land cover (LULC) dynamics and affect landscape sustainability around the Nile Delta of Egypt. The present study aims at evaluating and mapping changes in LULC and assessing the dynamics of LULC and Land Surface Temperature (LST) around the two branches of the Nile Delta, Egypt using Landsat data and GIS. Calibrated Landsat images were acquired on 2000, 2014 and 2019 and processed to produce LULC, environmental indices and LST, respectively, using ENVI 5.3. ArcGIS 10.1 was used to extract a transition map from 2000 to 2019 around the two branches. The results displayed that five classes of LULC were extracted around Damietta and Rosetta branches; water, urban, bare, dense and spare vegetation. A continuous increase in water was recorded around Damietta branch; 13.66 km2 (197%), 14.21 km2 (2.04%) and 16.54 km2 (2.30%) in 2000, 2014 and 2019, respectively. Also, urban area was increased around Damietta and Rosetta branch as follows: 53.6 km2 (7.72%), 58.34 (8.37%) and 90.37 km2 (13.70%) in 2000, 2014 and 2019, 59.55 km2 (6.809%), 104.16 (11.90%) and 149.77 km2 (17.11%) in 2000, 2014 and 2019, respectively. Urban achieved the highest gain of 24.807 and 85.70 km2 at the expense of dense vegetation around Damietta and Rosetta branch, respectively. The results showed that the decrease in vegetation and the increase in urban density lead to increasing LST of the study area. The changes in LST can be monitored depending on the construction materials such as the presence of green areas and topography. Urban and bare lands have the highest LST while the water bodies and vegetation temperature showed a tendency to decrease. It can be concluded that urban areas increased with annual rate 0.27 and 0.54 km2 and vegetation decreased with annual rate −0.57 and−0.55 km2 around Damietta and Rosetta branches from 2000 to 2019. Results showed that comprehensive index was 321.14 and 330.03 around Damietta and Rosetta branch, the higher the degree of development and exploitation. There has been a significant land use change which was due to an increase in population. Overall, this research provides valuable data about changes in LU/LC around the Nile Delta branches, it is very important for decision maker and stockholders for proper management.

Flow dynamics in large tidal delta of the Northern Dvina River: 2D simulation

A numerical modelling of flow dynamics in a tidal river mouth of comprehensive morphology is assumed to be one of the most effective methods of both scientific research and civil engineering projects. Realistic results of simulations can be obtained only on the basis of field observations. This approach is realized for a 2D hydrodynamic model of the Northern Dvina River mouth area. The Northern Dvina delta has a very complicated distributary network and suffers from both spring snow-melt floods and autumn storm surges. The STREAM_2D software package based on the 2D shallow water equations was used for the model development. The model was calibrated and validated on the background of water level data at state gauges and special water discharges measurements in the essential delta branches during the semi-diurnal tidal cycles. Sensitivity tests were provided to evaluate the most significant reasons for model errors. It was discovered that the distribution of roughness coefficients amidst delta channels and floodplain does not affect the flow dynamics in the delta significantly. However, the tidal range variations over a neap-spring cycle and mean sea level changes along the delta marine edge are of major importance.

Lena Delta hydrology and geochemistry: long-term hydrological data and recent field observations

The Lena River forms one of the largest deltas in the Arctic. We compare two sets of data to reveal new insights into the hydrological, hydrochemical, and geochemical processes within the delta: (i) long-term hydrometric observations at the Khabarova station at the head of the delta from 1951 to 2005; (ii) field hydrological and geochemical observations carried out within the delta since 2002. Periods with differing relative discharge and intensity of fluvial processes were identified from the long-term record of water and sediment discharge. Ice events during spring melt (high water) reconfigured branch channels and probably influenced sediment transport within the delta. Based on summer field measurements during 2005–2012 of discharge and sediment fluxes along main delta channels, both are increased between the apex and the front of the delta. This increase is to a great extent connected with an additional influx of water from tributaries, as well as an increase of suspended and dissolved material released from the ice complex. Summer concentrations of major ion and biogenic substances along the delta branches are partly explained by water sources within the delta, such as thawing ice complex waters, small Lena River branches and estuarine areas.

Estimation of the Volga Water-Divider Operation Impact on Runoff Distribution among the Volga Delta Branches

The present work is devoted to questions of the water-divider system application in the Volga River delta. Assessment of the water divider operation impact on runoff in the Buzan and Volga branches has been carried out both with conventional methods and with computations on the lower Volga hydro-dynamic model. High academic value of the paper has been determined by the right selection of all the hydro-dynamic model parameters in the conditions of insufficiency of the needed data on the flood regime.