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ŠUMARSKI LIST 11-12/2017 str. 27     <-- 27 -->        PDF

in which GeoWEPP was used for various land use types, there are no previous studies that consider only rangeland. Thus, this study will be one of the first researches that utilized GeoWEPP to estimate sediment yield and surface runoff for a study area covered by only rangeland in Turkey.
MATERIAL AND METHOD
MATERIJALI I METODE
Study Area – Područje istraživanja
The study area, Keklik watershed, is located 12 km away from the city of Kahramanmaras in the Eastern Mediterranean region of Turkey. Keklik watershed is covered by only rangelands. The bounding geographical coordinates of the study area are 36°52’ 30’’ to 37°37’ 30’’ north latitudes and 37°46’ 00’’ to 37°47’ 30’’ east longitudes (Figure 1). The watershed covers an area of nearly 780.83 hectares and there is no residential area in the basin.
Streams in the study area generally flow into the direction from North to South. The highest point of the study area is Köseburun Hill with 2084 meters and the lowest point is Güzlek Vineyards with 1200 meters of elevation. The region can be defined as a transition zone which has some characteristics of both Mediterranean climate and Continental climate. Thus, there are hot and dry summers and warm and rainy winters. Average annual precipitation of the study area is over 976.50 mm. Average, annual maximum and minimum temperatures are 41.1 ºC (July) and -10 ºC (February), respectively. In soil water balance; excess water is seen during January to March and the water deficit is seen during June to October.
According to soil maps which were produced by The General Directorate of Rural Service, the majority of the soils are consisted of Brown Forest Soils with Marn-Chalk and Reddish Brown Mediterranean Soils with limestone. The study area was used for grazing purposes. Uncontrolled and over capacity grazing over years has led to destruction of both herbaceous and climax vegetation significantly. There are number of endemic species (Astragalus akmanii, Polygonum ekimianum, Helleborus vesicarius, Echinops vaginatus, Ankyropetalum reuteri, etc.) in the study area; however, heavy grazing has negatively affected existence of these species. Besides, rangeland activities have been made without any soil and water conservation measures. As a result, actively continuing surface erosion is observed in the area, which is the main source of sedimentation.
GeoWEPP – GeoWEPP
GeoWEPP is a model that integrates WEPP v2006.5 model with TOPAZ (TOpography PArameteriZation), CLIGEN (CLImate GENeration) and GIS tool (ArcView 3.2) (Renschler, 2002) (Figure 2). TOPAZ was used to generate hillslope profiles by parameterizing topographic data based on DEMs. (Minkowski, 2007; Garbrecht and Martz, 1997) Sub-catchment profiles were produced by defining the channel network based on the steepest downslope path.
CLIGEN, a stochastic weather generation model, was used to generate various climate data including daily values of precipitation, temperature, relative humidity, and wind speed. ArcView 3.2 was used to generate the watershed outputs as grid layers representing soil loss as a percentage of the Tolerable Soil Loss (TSL). Then, the runoff and sediment yield data for each pixel were produced in grid outputs as well as in text files. Text files also indicated average annual rainfall, number of storms, and soil loss for each sub-watershed.