Rioni river mouth

The Rioni River mouth area belongs to the open deltaic type (Fig. 10) and comprises a protruding delta with a few branches and a deep nearshore zone. The delta head is near the water division sluice constructed at 7 km from the sea in 1959 for distributing river flow between the two main branches of the delta. The channel network of the Rioni mouth includes delta branches, the City Canal (left) and the Rioni-spillway (right). The City Canal, 7.5 km long, is divided into Northern and Southern branches separated by the Bol-shoy Island to form the old delta. The Rioni-spillway, 7 km long, is also divided into Northern and Southern branches separated by an island to form the new delta. The total area of the present-day delta of the Rioni River is about 20 km2. 

Some information on evolution, structure and regime of the Danube, Dniester, Dnieper, Rioni, Don and Kuban river mouths at the period up to the first part of the 20th century is given in [4]. More complete and present-day characteristics of the above-mentioned river mouths are considered in [5]. 

Main characteristics of the mouth area of the Dniester River are described in [10-12]. Natural and human-induced changes in regime of the combined Dnieper and Southern Bug rivers mouth area are studied in [13,14]. Very rapid and drastic changes of the Rioni delta due to engineering works are considered in [15]. 

Mouth areas of the Danube, Dniester, Dnieper and Southern Bug, Don, Kuban and Rioni rivers are the most important in the region of the Black Sea and the Sea of Azov. Mouth areas of these rivers differ from other mouths not because of only their large size and a great diversity of landscape. These river... 

The rate of the RSLR in the Black Sea and the Sea of Azov and at their river mouths (Table 3) varies over a wide range [3,8,24-26]. These data show that actual eustatic sea level rise increased with time and by the beginning of the 21st century reached in the Black Sea 4 mm year x. Besides, these data confirm the assumption that the land subsidence plays very important role in the RSLR in river mouth areas and can reach 3-6 and even 12 mm year-1. The most values of the RSLR and subsidence are typical of the coastal parts of the Danube and Rioni deltas (Table 4). 

Fig. 10 Scheme of the mouth area of the Rioni River. 1 - old delta, 2 - new delta, 3 - port, 4 - sea approach canal, 5 - submarine canyon. Delta branches 6 - Northern ( old delta) 7 - Southern ( old delta) 8 - Northern ( new delta) 9 - Southern ( new delta). 10 - Water division sluice... 

In modern times, the development of the protruding delta of the Rioni River has been as follows [15,28] the old55 delta was formed at the Rioni mouth before the diversion of river flow in 1939 (the data on the progradation of the old55 delta are very scarce) and a new55 delta was formed at the mouth of the Rioni-spillway after 1939 the old55 delta virtually inherited the distinctive hydrographic features of the ancient times (two branches, Northern and Southern), divided by the Bolshoy Island. 

The flow bifurcated into the Northern and Southern branches of the new delta and, later, an island was formed (Fig. 11c). By its dimensions and outlines, this island closely resembles Bolshoy Island, which was formed at the mouth of the main channel of the Rioni River in the old delta. 

The open nearshores of the majority of the rivers under study are deep. Mean slope of the open nearshore bottom at the Rioni mouth is 6.5%o ( old delta) and 14.3%o ( new delta) [3]. Less deep are the open nearshores of the Danube and Kuban rivers [3,5]. The open nearshores of this kind are typical of the Dniester, Dnieper and Don mouths [5]. 

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