Nowadays, the development and widespread use of computer technologies and thus the easier access of researchers to earth data have caused morphometry studies to gain a new dimension. The integration of Geographic Information Systems (GIS) software and satellite images has provided the opportunity to perform also morphometric analyses more practically (Ajay et al., 2014; Rai et al., 2018; Obediat et al., 2021).
It is known that morphometric parameters are used for a wide variety of purposes in geomorphology studies (Morisawa, 1959; Hack, 1973; Zavoianu, 1985; Baker et al., 1988; Patton, 1988; Turoğlu, 1997; Cürebal, 2004; Özdemir, 2007; Elbaşı and Özdemir, 2018; Ege et al., 2019; Bogale, 2021; Esen and Tonbul, 2022). The main ones are these: understanding the systematics of land relief, explaining geodynamic and geomorphological processes and their concrete evidence of these in the area quantitatively -such as revealing the relationship between fluvial processes and tectonism- and to question the effect of elements such as vegetation and lithological structure on these processes. With all of these thus determining torrent and flood susceptibility situations can be achieved quantitatively with morphometric index and analysis (Turoğlu, 1997; Özdemir, 2007; K. Pareta and U. Pareta, 2011).
Drainage analyses constitutes an important part of morphometric analyses (Table 1). With drainage analyses, the hierarchical status of rivers and their tributaries can be determined, providing the opportunity to conduct more detailed studies on those that pass through important settlements. Important features such as the shape of drainage basins, the pattern of streams, bifurcation rates and the slope conditions of the river bed provide information about the state and behaviour of the hydrological structure in the region (Rastogi and Sharma, 1976).
Behavioural characteristics of tributaries in basins; the strength of erosive activities, sediment load, and flood susceptibility play a decisive role. And with morphometric analysis, the mission of these factors can be defined with high accuracy, especially on the basis of sub-basins (Esen and Tonbul, 2022). Obtaining the morphometric characteristics of a drainage basin provides general information about the behaviour of stream branches and can be effectively evaluated in designing the appropriate type of soil and water management system for the site, detecting areas prone to erosion, torrent/flood analysis and determining suitable site selection for different engineering structures. In addition, the preservation of ecological integrity- inputs and outputs of the basin; it contributes to sustainability by taking into account water, sediment, nutrient and pollutant potential (Dutta and Sharma 2002; Oyegoke and Ifeadi, 2008; Waikar and Nilawar, 2014; Bogale, 2021).
Especially in the Bozburun Peninsula, which has become an important centre of attraction in terms of tourism since the 1980s; thanks to the evaluation of the existing relief formed by the interaction of tectonism, lithological and hydrological structure with morphometric parameters, it has been understood that the sub-basins, which host a significant part of the population in the region, have significant levels of susceptibility in terms of torrent and floods disasters (Ege et al., 2023).
Table 1
Morphometric parameters used in the study. In the harmonic slope of the basin, the average slope of the important river beds of the 4th index and above, crossing the settlement centers, was calculated.
Parameter
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Formula
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References
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Linear morphometry
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1- Bifurcation ratio (Br)
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Br = Nu/Nu+1
Nu = Number of orders in the river basin
Nu+1= Next total number of stream orders
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Schumm, 1956
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2- Texture ratio (T)
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T = Nu1/P
Nu1= Total number of first order streams;
P = Perimeter of basin (km)
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Horton, 1945
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Areal morphometry
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3- Drainage density (Dd)
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Dd= L/A
L= Total length of streams (km);
A = Area of basin (km2)
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Horton 1932,1945
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4- Basin shape (Bs)
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Bs=A/Lb2
A = Area of basin (km2);
Lb= Length of basin (km)
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Horton, 1932
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Relief morphometry
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5- Basin relief (Bh) and relief ratio (Rr)
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Bh=Hmax -Hmin
and
Rr =Bh/Lb
Bh= Basin relief (m)
Lb= Length of basin (m)
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Schumm, 1956
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6- Roughness value (Rn)
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Rn= Bh*Dd
Bh= Basin relief
Dd= Drainage density
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Schumm, 1956
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7- Time of concentration (Tc)
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Tc= 0,00032*(L0,77/S0,385)
L = Maximum length of river bed (m)
S = Harmonic slope
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Kirpich, 1940
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8- Hypsometric curve and integral (Hi)
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Hypsometric curve = h/H and a/A
h = Relative altitude
H = Total altitude; a = Relative area
A = Total area
Hi= (Hmean-Hmin)/(Hmax-Hmin)
Hmean=Average altitude, Hmin= Minimum altitude,
Hmax= Maximum altitude
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Pike and Wilson, 1971
Mayer, 1990
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9- Basin slope (Bsl)
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S= (10/ ∑1/√Si)2
S = Harmonic slope of the river bed and
Si=Indicates the harmonic slope between sections
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Kirpich, 1940; Mockus, 1961
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1.1. Study area
Bozburun Peninsula is located within the borders of Marmaris district, between latitudes 36⁰33ꞌ-36⁰55ꞌN and longitudes 27⁰57ꞌ-28⁰19ꞌE. The peninsula; from the west, it neighbors the Datça Peninsula, which also has a coast to the Gulf of Hisarönü. The area is included in the Aegean Sea from the west and the Mediterranean coast from the east. Marmaris city centre (since it is constantly on the agenda with flood disasters) was included in the Bozburun Peninsula by following the water division line. In order to achieve this; The water division line started from Balaban Mountain (998 m), which surrounds the city from the east and the Gulf of Marmaris from the northeast, was continued to the north of Hisarönü Gulf. In this way, the northern border is completed in a generally convex appearance between the Marmaris Gulf and Hisarönü Gulf, including the Marmaris district centre (Figure 1). The field has a projection area of 440 km2 according to measurements made in Google Earth Pro and Arc Map 10.5.
1.2. Geological features
The research area, which together with the Datça Peninsula constitutes the southwesternmost part of Turkey, is shown within the Anatolide-Tauride tectonic union in the paleotectonic classification of Turkey. The peninsula, which is an extension of the Western Taurus Mountains, is located on the border of the subduction zone, which was formed by the collision of African and Eurasian plates in the NE-SW direction, starting from the neotectonic period (Şengör and Yılmaz, 1981; Ketin, 1983). This zone covers an important region called the Hellenic Arc, which is an important tectonic belt in the Aegean Sea and produces active earthquakes and volcanic activity, including the study area (Pichon and Angelier, 1979; Şengör and Yılmaz, 1983; Jackson and McKenzie 1984; Gönenç and Akgün, 2012; Tur et al., 2015).
Faults in the field; they are normal, reverse and strike-slip faults. The extensions of the faults are mostly in the "E-W, ENE-WSW" direction. However, at many points, a different fault cuts this extension at a vertical or almost vertical angle. In this sense, the Bozburun Peninsula reflects the complex tectonic features of the Southwest Aegean (Koçyiğit, 1984, 2000; Sözbilir, 2005; Westaway et al., 2005; Nazik and Tuncer, 2010; Nazik and Poyraz, 2015; Günhan et al., 2018).
The study area and its immediate surroundings also represent an important region where the Bodrum Nappe, Gülbahar Nappe and Marmaris Ophiolitic Nappe, which belong to the Lycian Nappes, are exposed. Since ophiolites occupy a large area, especially in the Marmaris, Armutalanı, İçmeler, Turunç and Kazandere basins, the infiltration capacity of the ground can be considered low. In the central and southern parts of the peninsula, there are mostly Mesozoic period limestones of neritic origin (Şenel and Bilgin, 2010). This section covers important karst areas in the region and the ground-surface water relationship seems to be intensely established in these areas. It is possible to encounter specific traces of tectonic and lithological relationships in the formation of drainage networks in the sub-basins identified on the peninsula (Ege et al., 2023). It has been observed that the resulting drainage types are generally fault-controlled dendritic drainage. In the Kazandere sub-basin, the caged drainage type emerged as the area exhibited a nearly homogeneous appearance and different faults cut each other at almost vertical angles. Flood plains observed in many sub-basins in the field (Marmaris, İçmeler, Armutalanı etc.) and specific slope breaks between slopes provide an important idea as natural boundaries in the separate formation of “torrent” and “flood” disaster (Cürebal, 2004; Geçen and Balcı, 2022).
1.3. Climate features
A typical Mediterranean climate is experienced in the area. The winter months in the peninsula and its immediate surroundings are warm and rainy, and the summers are quite dry (Csa) (Köppen, 1936). During transition seasons, thunderstorms occur from time to time depending on frontal conditions. According to the climate data of Marmaris Meteorology Station, the annual average temperature is 18.8 ⁰C and the total precipitation is 1218.5 mm (MGM, 1992–2015) (Fig. 2).
Significant increases in precipitation intensity are also recorded in the autumn and winter seasons. Classified by the average number of days of rainfall intensities for many years: for the month of September; between 25–50 mm (light showers) 6 days; between 50–100 mm (showers) 2.2 days; 100 mm+ (heavy showers) for about 1 day. For October; it takes 3 days between 25–50 mm, about 1 day between 50–100 mm, and about 0.5 days between 100 mm+. For November; 3 days between 25–50 mm; about 3 days between 50-100mm; 100 mm+ is about 1 day. For December, the month with the most rainfall; about 6 days between 25-50mm; about 3 days between 50–100 mm; 100 mm+ is about 1 day. For January, it was calculated as 5.27 days between 25–50 mm, 2.1 days between 50–100 mm, and 0.6 days above 100 mm (severe showers) (Fig. 3). Accordingly, there were 19 important torrent and flood disasters [(November (3), December (5), January (7), February (2), March (2)] recorded in the area (1941–2023) (BCA, 1941–1957; AA, 2004–2023; MGM; 1992–2023).
1.4. Soil features
The most common soil type in the study area is Red Mediterranean Soil (Terra Rossa) with an area of 142 km2. These soils are followed by Red-Brown Mediterranean soils with 94 km2. This soil group in terms of area size is as follows; It is followed by Limeless Brown Forest Soils with 92 km2, sparsely formed soil and bare rocks with 85 km2, Colluvial with 22 km2, Alluvial with 4 km2 and Chestnut Colored Soils in a very small area of 1 km2 (OGM, 2021).
1.5. Vegetation and land use characteristics
The tree with the widest stand spread in the area is pinus brutia. Pinus brutia are proportionally followed by maquis species, and maquis are followed by garigs (OGM, 2021) (Fig. 4). However, in the 2021 forest fires, a significant part of the pinus brutia trees in the area burned (12500 ha were directly damaged in the fire, and a significant portion of the burned areas pinus brutia) (Tüfekçioğlu et al., 2022).
Using land cover/use data from Copernicus Global Land Service for the years 1990 and 2018, it was determined that there were significant changes in temporal distribution according to the outputs of the land use maps created in the ArcMap 10.5 program. It has been observed that there has been a significant increase, especially in the settlement areas in flood plains. During the field studies, it was determined that the stream lines were subsurfaced in some places and many unhealthy crossings/structures were built in the stream beds. Important irrigated agricultural areas are also under uncontrolled construction. The main reason for this can be shown as the uncontrolled growth of tourism facilities in the Aegean and Mediterranean Coasts, without taking into account the natural structure, with the Tourism Incentive Law enacted in 1982.