Based on Great Soil Group and combination of soil properties, soil depth
is defined. After having on the Great Soil Group and depth, percentage
of clay, sand and silt amount are defined according to determination
soil properties study of Ardas and Creutberg (1995) in Turkey. Soil
texture is determined by using soil texture triangle (Ley et al. 1994).
The USLE equation soil erodibility (K) factor (USLE_K) was established
with respect to the soil textures. The value of USLE_K is between 0.1
and 0. A value of < 0.02 shows a soil of low erodibility; 0.02
- 0.04 shows moderate erodibility; and > 0.04 shows high
erodibility. When the silt content of soil type increases, it can become
more erodible regardless of whether there is a comparable reduction in
the sand or clay fraction (Rosewell 1993). The soil bulk density
(SOL_BD) values employed in SWAT database are defined based on soil
texture groups by using Guides for Editing Soil Properties (2005). The
soil available water capacity (SOL_AWC) has been defined by using soil
texture groups, as described in Ley et al. (1994). The soil hydraulic
conductivity (SOL_K) has been determined based on soil texture group,
as suggested by Guidelines for Soil Description (Jahn et al. 2006) (Fig.
1c). After these processes, SWAT-relevant soil database of the basin was
generated.
Landuse/landcover
Three different data, land-use/ land cover map produced by Kocaeli
Buyuksehir Municipality, crop cultivation data of Kocaeli Provincial
Directorate of Agriculture, land-use/ land cover created by the Ministry
of Agriculture and Forestry within the framework of the STATIP project,
were used to generate the land-use/ land cover map of the study area due
to having some challenges about these data such as definitions of land
use/land cover, lack of crop pattern, etc. The project data map was
generated by using SPOT satellite data with 5 and 2.5-meter resolution
on the 1/25000 topographic map. Although the spatial resolution of
STATIP project land use/landcover map is good, the definition of
absolute irrigated agricultural areas, dry absolute agricultural areas,
marginal irrigated agricultural areas and dry marginal agricultural
areas cause confusion about agricultural products in the basin. These
definitions were made based on the framework of the Regulation on the
Conservation, Use and Planning of Agricultural Lands (Official Gazette
2017 no: 30265). Marginal agricultural land means private croplands and
planted lands where traditional tillage agriculture cannot be carried
out due to soil and topographic limitations. “Absolute” agricultural
land means that the land is currently suitable for agricultural
production in terms of the physical, chemical, and biological properties
of the soil, non-limiting, no or very little topographic restrictions.
In addition, irrigated agricultural land is defined as that the land
where additional water needed by the cultivated plants during the
growing phase. Although land-use/land cover map produced by Kocaeli
Buyuksehir Municipality includes just hazelnut and agricultural areas,
there is no specific definition about crop production in the
agricultural areas. Crop cultivation data of Kocaeli Provincial
Directorate of Agriculture is represented by points instead of areas
based on villages in the basin as ton/year production. Thus, the
land-use/cover map was produced by combining these data in GIS
(Geographic Information System) (Fig. 2). Based on the produced map,
there are mostly wheat and evergreen broadleaf forest areas. Hazelnuts
are not in SWAT database, so these crops are defined as shrubland since
hazelnut is in the shrubland flora.
Meteorological data
NCEP/CFSR (The National Centers for Environmental Prediction/Climate
Forecast System Reanalysis) data were used to obtain meteorological data
of the study area. These data have advantage that they come along with
in situ measurements from several ground stations. Meteorological data
handled from the station near the study area is between 1979 and 2014
years in the daily time step.
Pollution Sources
There are 3768 sheep and 3006 dairy cattle in the Namazgah Dam basin
based on TUIK data that was obtained from villages in the basin (Fig.
3). The amount of manure caused by poultry, cattle, and sheep were
calculated using coefficients used for animal pollution loads as
suggested by Uttormark et al. (1974). Animal-based fertilizer
calculations were made for villages for three different animal
categories: poultry, cattle, and sheep. The average coefficients for
cattle were determined for beef and dairy cattle to calculate manure
since cattle are not divided into precisely beef and dairy cattle in the
basin.
Wheat cultivation is carried out in many different soil types. The pH of
the soil is very important in terms of plant nutrition and
fertilization. The best development environment for wheat plants is in
soils with neutral pH (6.6-7.3). In addition, one of the most
significant factors affecting wheat yield is the amount of precipitation
and the distribution of precipitation during the growing period. Thus,
the amount of nitrogen fertilizer per decare (da) during the development
period of the wheat should be given based on these factors. Top
fertilization in wheat cultivation is carried out in October or before
and in the spring. 26 kg/da nitrogen, 8.5 kg/da phosphorus, and 0.96
potassium kg/da are given in October or before to make balanced
fertilization in wheat and barley cultivation in the basin.
Fertilization for the hazelnut cultivation is carried out as 2.7
kg/m2 nitrogen, 0.8 kg/m2 phosphorus
and 0.09 potassium kg/m2 on March. The fertilizer
amount applied to each crop in the basin was determined by considering
the Kocaeli Agriculture Provincial Directorate Fertilizer guideline.