On the basis of the current relief and paleographic reconstruction in the region “Ruen threshold” are get new proves which confirm the expressed opinion of  for the decapitation of Almadere River (within basin of Luda Kamchia River) by Hadjiiska River.
For first time are produce geological, geomorphological and paleographic evidence about epigenetic origin of the defile parts of the valleys formed by Luda Kamchia River Boazdere River (the Big River) and their feeders in the east parts of East Stara Planina Mountains morphpostructural zone.
The decapitation - represents decapitation (river catchment) of a river valley or seizing the flow of one river valley by another one.
Mostly the more deep incised valley by regressive erosion reaches to the river bed of another river in its catchment basin parts (main decapitation) or in its middle parts (lateral decapitation) and bears down the water flow of the another river in its own river bed. The decapitation can be caused by tectonic reasons.
The valley of Hadjiiska River (till 1942 – Hadjidere River) is formed onto the axis of the same named Hadjiiski Graben which is developed onto the bigger fault – Prosenik Graben. The river take its source from one spring – fountain located 2 km southward from Dobra polyana village in Eminska Mountain. Initially it flows from west to east direction in narrow valley. Near to the village of Galabets it turns in south – east direction it spreads in wide alluvial valley. It length is 55,3 km and its catchment area is 356 km2. The average gradient of the river bed is 9,5 %. Its biggest feeder is Byala reka River (23,1 km). It run into Black Sea near to “Slanchev bryag“ resort – northward from Nesebar town.
Significant interest are the spring sources of Hadjiiska River northward from Ruen village. There is low plane water shed between the catchment basins of Almadere River and Hadjiiska River (Fig. 1).
There are different opinions regarding the relations between them during the Late Pliocene and Pleistocene epochs.
Radev  launched the idea that Hadjiiska River catches the spring sources of Almadere River. He showed that both springs of Hadjiiska River take source from Eminska Mountain westward from “Kodjagioldjuk” place join along together about hundred meters toward one saddle between hill – 326,1 m and “Uzundjakairqk” peak. The initial direction is in west- south – west i.e. toward Almadere River – opposite of Hadjiiska River stream. After their flowing these feeders forms Ilimdere River which flows in westward and forms narrow defile. After leaving the defile it makes sharp tun in eastward and run into Hadjiiska river valley.
Besides the foregoing author has underlined that from Rujitsa village (Chavdarlaka) upward till the mouth of Ilimdere river and higher near Nadur village in Hadjiiska river valley (Adjidere) have formed narrow and deep “gorges – defiles“.
This facts according the author of this article is an indication for faster incising of the main river as result of reduction of the main erosion basis – Black Sea.
According Radev  in stated above facts show that it has done decapitation of Boazdere River (now The Big River) and its initial part together with the main feeder Ilimdere River have joined into Hadjiiska river valley.
According [2-3] in this hydrographic node has represented decapitation of the spring sources of Hadjiiska River by Almadere River (feeder of Luda Kamchia River). In maintenance of this opinion they produce the following evidence:
The initial feeders of Almadere River (Vresovska River) and Hadjiiska River are toward to Hadjiiska River – respectively Nesebar bay.
Pliocene- Pleistocene levels onto their valley slopes correspond to the level of the Ruen threshold (swell).
Kodjadere and Vresovska Rivers run onto Almadere River at 95° and 90° each.
Almadere River forms narrow defile in Eminska Mountain between Kitka resort and Shivarovo village and the gradient steep till its flowing into Luda Kamchia River near Duskotna village.
According foregoing authors these facts are reliable indication for the decapitation of Paleo- Hadjiiska River by Almadere River. The cause for this is hidden in the more active incising of the river as result of the bigger gradient, the nearer local erosion basis of Luda Kamchia River and by the more active incising into weak- solid paleogenetic deposits in Lyulyakovo – Duskotna Lowering.
As well and the longitudinal profile of Paleo-Hadjiiska River has been with low gradient and the coast line has been jutted into the sea than the current one is.
The authors draw a conclusion that the decapitation has done after Middle Pleistocene Epoch (probably Guryi or Low Chauda Epoch).
In result of analysis of the topographic maps in scale 1: 25 000, the current geological – geomorphological data for this hydrographic node the author of this article has opinion that Hadjiiska River has caught (occupied) the spring parts of Almadere River in Eminska Mountain west ward from “Kodjagioldjuk“ place and northward from hill 394,1 m (Fig. 1).
The decapitation has been done northward from Ruen village at the foot of “Uzundgakairiak” peak i.e. the statement of  is well – grounded and reliable.
It is possible that Ilimdere River gorge  in Eminska Mountain also to has epigenetic origin, which prove a point (in addition the clear westward direction) that it is old and has been part of Almadere basin. The left feeders of Almadere have better developed river – valley network but the right ones are few in number and most of them are with episodic flow, disappearing into the deposits of dilluvial – proluvial cover plain at the foot of Eminska Mountain.
Genesis. During the period after Middle Eocene epoch till the beginning of Oligocene epoch in result of Ilirian Orogenesis in East Stara Planina Mountains morphostructural zone (ESPMZ) have formed set of positive morphostructures which gave the characteristics of a high elevated mountain conformed relief. At the end of this period the current water area part has swept in the sinking and spreading of the Black Sea Valley. In result of change the sign of the tectonic movements the east part of ESPMZ have spread in sinking and have overflowed by the water of Upper Eocene basin. Its sediments have sealed up Ilirian structures and this way had formed wide Upper Eocene sedimentary area with regional gradient north- north – east direction.
In the beginning of Oligocene the located northward Down Kamchia Lowering has distinguished with anticipated rate of consedimentaral sinking toward the rising of East Stara Planina Mountains.
In result of this the water of the Upper Eocene basin have receded in north- north- east direction. Following the receded coast line onto the Middle – Upper Eocene sedimentary area has arisen river – valley network prototype of Luda Kamchia River and Boazdere (The Big River) and their feeders.
After reduction in the main erosion basis – Black Sea Valley (respectively Down Kamchia Lowering) initially the rivers have incised into weak resistant flysh sediments and later have incised into solid hard limestones formed the structures of ESPMZ and this way have formed set of epigenetic defile valleys.
The border – Pliocene- Eopleistocene Epoch (Chauda) has synchronized with activities of Wallachia tectonic phase. In consequence of an active tectonic conditions related to smooth rising of the land during the young Alpine cycle and with the sinking of the deep water Black Sea Depression has registered one of the deepest regressions.
It has dried a big part of the coastal land. It has begun development of the second generation river- valley systems in our coast. In ESPMZ they are – Dvoinica River, Hadjiiska River etc.
Conclusion.Bear in mind that Prosenik Graben is filled with Pliocene an continental Quaternary deposits (formed during Vilafrank) shows that Hadjiiska River has arisen later – during Eopleistocene Epoch (Vilafrank). During Pliocene – Pleistocene epoch when has enforced the leading role of the negative movements in Black Sea Valley – Hadjiiska River valley has incised faster into weak soldered Pliocene and Quaternary sediments than Almadere River which has already formed and has incised into solid hard rocks in its defile in Eminska Mountain.
Besides this the mouth of Hadjiiska River has been closer to the main erosion basis – Black Sea and it has reacted first. The water catchment of Hadjiiska River is bigger. The fast incising of Hadjiiska river valley is evidence with many protruding river -valleys and ravines (protruding slopes) onto the southern slope of Eminska Mountain i.e. there is superiority of the endogenetic processes over the exogenetic ones.
Though Luda Kamchia (local basis of Almadere River) has incised into weak resistant deposits filled in Lyulyakovo – Duskotna Depression, Almadere River flows in the beginning of the defile despite of it has incised into limestones, sandstones, marls and has also incised into thick stratum flysh (sandstones, aleurolites, clay marls, limestone clays). It has retarded its incising than the incising of Hadjiiska River into unstable Pliocene rubble, sandstones and clays.
Probably the defile which outline the border between Eminska Mountain and Karnobat Mountain has epigenetic origin. Besides, the defile of Almadere River is next to Luda Kamchia River defile.
It is run into Luda Kamchia River before Duskotna village – in the beginning of Luda Kamchia River defile. That suggest to us that like Luda Kamchia River and Almadere River as its feeder initially has flowed onto easy disintegrated (amenable to erosion) rocks and after reduction of the main basis – Black Sea Valley has incised into solid hard limestones and this way has formed epigenetic defile in the western part of Eminska Mountain.
The Almadere River defile has formed at the same time and in the same manner as Luda Kamchia River defile.
 Radev, J. In: Annuaire de l’Universite de Sofia “St. Kliment Ohridski”, Faculte de geologie et geographie, Livre 2 – Geographie, 1926, 23, 1-119
 Baltakov, G., Choleev , I .In: Annuaire de l’Universite de Sofia “St. Kliment Ohridski”, Faculte de geologie et geographie, Livre 2 – Geographie, vol. 92 ,2001, 53-77
 Baltakov , G. In: Annuaire de l’Universite de Sofia “St. Kliment Ohridski”, Faculte de geologie et geographie, Livre 2 – Geographie, vol.96, 2003, 69-86