GEOMORPHOMETRIC ANALYSIS OF LIMONLU AND ALATA WATERSHEDS (ERDEMLI, MERSIN, TURKEY)

Abstract

Geomorphometric analysis deals with the measurement and mathematical analysis of the earth's surface (Hengl and Reuter, 2009: 1; Pareta and Pareta, 2011: 1). It has provided some means to better understand different topographies on which humankind shaped his life by using actual tecnologic data (Ozdemir, 2007: 2; Pedrera et al., 2009: 2; Curebal and Erginal, 2010: 203; Utlu et al., 2012: 769). Remote Sensing and GIS techniques are efficient tools for the delineation, updating, and morphometric analysis of drainage basins (Rowberry, 2008:28-29; Curebal and Erginal, 2010: 204; Monterio et al., 2010: 17; Bayraktar, 2012: 48; Bekaroglu, 2014: 334-344; Waikar and Nilawar, 2014: 1). The aim of this study was to analyze the development and formation of geomorphological properties of the basins between Limonlu and Erdemli using the geomorphometric indices. In the present study, morphometric analysis was utilized based on the GIS technique. Firstly, DEM model of the area was produced and then, all calculations of geomorphometric indices were carried out using this model. As a result, it was found that the effect of lithology had been decisive in the development of basins and that neighbouring streams had not only different properties but also similar features. In the study, Limonlu and Alata watersheds were examined by using different geomorphometric indices. Morphometric parameters used in the study were stream gradient index, drainage density, stream frequency, The Valley Width-to-Height Ratio (Vf), basin shape ratio, head load index, surface-area ratio index, surface-form index, topographic roughness index, composite topography index, hipsometric curve and integral value, and slope position classification. One of the geomorphometric analysis is Hypsometric curve and its integral value analysis (Strahler, 1952: 1117-1141; Bayraktar, 2012: 49; Kucukonder, 2012; Utlu et al., 2012: 771; Bekaroglu; 2014: 334-335). It is the relative part of area at different elevations within a region. The hypsometric curve shows the relative proportion of basin area below or above a given height. The hypsometric integral represents the area under the hypsometric curve. In the current study, Hypsometric curve and integral values for Limonlu and Alata watersheds were determined (Fig. 7). Hi values for Limonlu watershed’s was 0.64 and it was calculated as 0.54 for Alata watershed. Stream gradient index is very usefull to determine the tectonic effect on the landforms. The computation of SL is based on the interpolation of a discrete value. For a segment of a given river, the SL is defined as SL= (dH × L)/dL where dH is the change of elevation, dL is the horizontal length of the segment, L is the total channel length from the midpoint of the segment where the index is calculated, upstream to the water divide (Leopold, et al., 1963; Hack, 1973: 421-429; Keller and Pinter, 2002; Knighton, 1984; Curebal and Erginal, 2010: 203-210; Font, 2010, Vago, 2010, Fig. 4). Generally, the data needed to compute SL are measured from topographic profiles. Depending on the development stage of the watershed, the curve of a young immature watershed offers a convex form and a high integral value. In mature watershed case, the curve takes a concave shape upstream, convex downstream, and an integral lower compared to the previous case (Font et al., 2010). With another geomorphometric analysis, the results showed that Alata had more roughness due to the erosion happened more easily (Fig. 13). The drainage density which is expressed in terms of Km/Km2 indicates the closeness of spacing of canals, thus providing a quantitative measure of the average length of stream canal for he whole basin. The results showed that lithology had an important role on drainage density. Because Alata watershed has ophiolite, its drainage density index value was found to be 0.34 km/km2 but Limonlu watershed had limestone and its value was 0,17 km/km2. To determine the tectonic effect on the landforms, commonly the Valley Width-to-Height Ratio (Vf) index has been used (Knighton, 1984; Keller and Pinter, 2002; Sarp et al, 2006: 2-5; Curebal and Erginal, 2010: 203-210). Valleys have been classified according to Vf value. V-shaped valleys are common in areas of active uplift and deep, linear stream incision (low Vf values, often ≤ 1). U-shaped valleys are representative of formerly glaciated or tectonically stable areas where stream valley bottoms tend to be wider (often ≥1.5) Vf values (Sarp et al., 2006; http://gis4geomorphology.com). According to the analysis results, almost all of the measured Vf values were ≤ 1. Today, many geomorphometric indices also benefit from GIS calculations and very rich visual data can be obtained using GIS. One of these is the slope position index classification (Tagil and Jennes, 2008: 910-921; Reu et al., 2013: 39-49). The results showed that the region had the highest slope close to Koramsali village which had the most physical crumbles. (Fig. 12). In addition, based on other geomorphometric indices maps including head load index, surface-area ratio index, surface-form index, topographic roughness index, and composite topography index, it was found that the region close to Koramsali village was very important area (Fig. 13,14, 15). To sum up; there were many factors effecting erosional processes in both watersheds. But most important of them, the Karaisali Limestone did not have same thickness in whole area. It had variable thickness and its tickness increased from east to west (Gorur, 1973: 227-232; Unlugenc and Demirkol, 1988: 17-24).

Özet

İnsanoğlunun üzerinde yaşamını şekillendirdiği farklı topografyalar, güncel ve teknolojik veriler kullanılarak Jeomorfometrik analiz yöntemleriyle daha iyi bir şekilde anlaşılır. Bu bakımdan Limonlu ve Alata havzalarının gelişim süreçlerinin jeomorfometrik indisler yoluyla anlaşılmasının amaçlandığı çalışmada; ilk olarak çalışma sahasına ait bir sayısal yükseklik modeli (SYM) oluşturulmuş; belirlenen jeomorfometrik indis hesaplamaları, bu model üzerinden gerçekleştirilmiştir. Çalışmada kullanılan morfometrik analizler; Akarsu-Boy gradyan indeksi, drenaj yoğunluğu, akarsu sıklığı, Vadi tabanı-Vadi genişliği (Vf) Oranı indeksi, havza şekil oranı, ısı yükleme indeksi, yüzey-alan oranı indeksi, yüzeyşekil oranı indeksi, topografik pürüzlülük indeksi, topografik bileşke indeksi, hipsometrik eğri ve integral değeri, eğim pozisyonu sınıflamasıdır. Jeoloji haritasından faydalanılarak litolojinin havza oluşum ve gelişimine etkisi değerlendirilmiştir. Sonuçlar drenaj yoğunluğu üzerinde litolojinin önemli bir rol oynadığını göstermiş; Ofiyolit birimler üzerinde yer alan Alata Deresi'nin 0.34 km/km2 drenaj yoğunluğu indeks değerine karşın; kireçtaşları üzerindeki Limonlu için drenaj yoğunluğu indeks değeri 0.17 km/km2 olarak hesaplanmıştır. Aşınım seviyesini gösteren bir parametre olarak Hipsometrik integral değeri Limonlu havzası için 0.64 ve Alata için 0.54 olarak hesap edilmiştir. Sonuç olarak; havzaların gelişiminde litolojinin etkisinin büyük oranda belirleyici olduğu; komşu akarsuların benzer özelliklerinin yanında farklılaşan yanlarının da bulunduğu tespit edilmiştir. Ancak bunlardan en önemlisi her iki havzada da geniş bir yer kaplayan Karaisalı kireçtaşı formasyonunun kalınlığının her yerde aynı olmaması; doğu-batı doğrultusunda değişken bir kalınlığa sahip olmasıdır. Karaisalı Kireçtaşı Formasyonu doğudan batıya doğru giderek artan bir kalınlığa sahip olması, havzaların aşınım özelliklerini etkilemektedir