## 2 Irrigation System  
The amount of water that needs to be used should be calculated as accurately as possible in order to make irrigation projects more effective. Essential for calculating the irrigation water requirement is knowledge of evapotranspiration [33; 34]. The storage and capacity of the system transmission structure are projected and constructed according to this knowledge. The healthy way for calculating of evapotranspiration is to use one of the direct measurement methods. However, researchers have developed analytical equations that can be used to estimate the evapotranspiration due to the high cost and time demands of the direct measurement method. The United Nations Food and Agriculture Organization (FAO) recommends the Penman Monteith method to determine the crop water requirement for assisting the sizing of the irrigation projects in developing countries. It is aimed to calculate the healthy evapotranspiration with the crop coefficient (\(k_{c}\)) determined by the climate and soil data of the irrigation area. The reference evapotranspiration(\(ET_{o}\)) has been used, and required climate data has been obtained from the website of the Turkish State Meteorological Service (www.mgm.gov.tr) in order to use the FAO Penman Monteith method [33]. \[ET_{o}=\frac{0.408\times\Delta\times(R_{n}-G)+\gamma\times(\frac{900}{T+273}) \times u_{2}\times(e_{s}-e_{a})}{\Delta+\gamma\times(1+0.34\times u_{2})} \tag{1}\]  
Here, \(ET_{o}\): Reference evapotranspiration (mm day\({}^{-1}\)), \(R_{n}\): Net radiation (MJ m\({}^{-2}\) day\({}^{-1}\)), \(G\): Soil temperature flux density (MJ m\({}^{-2}\) day\({}^{-1}\)), \(T\): The average daily air temperature (\({}^{\circ}\)C), \(u_{2}\): 2 m height wind speed (m s\({}^{-1}\)), \(e_{s}\): Saturated vapor pressure (kPa), \(e_{a}\): Actual steam pressure (kPa), \(\Delta\): The slope of the vapor pressure curve (kPa/\({}^{\circ}\)C\({}^{-1}\)), \(\gamma\): Psychometric constant (kPa). Climate data obtained from the meteorological station 17084 belongs to Corum/Center and is shown in Tables 1 and 2. This data is used to define the water requirement necessary for crops to be grown. The reference plant is walnut for FAO Penman Monteith method. Evapotranspiration values for walnut have been calculated as follows [33; 34];  
\[Et_{c}=k_{c}\times ET_{o} \tag{2}\] \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Country** & **Corum** & **Latitude** & **40.37 \({}^{\circ}\)N** & **Longitude** & **Station** & **Merkez** \\
**Altitude** & **840 m** & & & **34.53 \({}^{\circ}\)E** & & \\ \hline
**Month** & **Avg. Temp \({}^{\circ}\)C** & **Humidity \%** & **Wind km/day** & **Sun Hours** & **Rad MJ/mm\({}^{2}\)day** & **ET\({}_{o}\) mm/day** \\ \hline January & \(-\)0.6 & 76 & 1 & 1.9 & 5.3 & 0.39 \\ February & 1.1 & 74 & 2 & 1.9 & 6.9 & 0.58 \\ March & 4.9 & 67 & 2 & 3.4 & 10.8 & 1.08 \\ April & 10.5 & 62 & 2 & 3.2 & 12.9 & 1.70 \\ May & 14.9 & 61 & 2 & 4.1 & 15.6 & 2.41 \\ June & 18.4 & 57 & 2 & 7.0 & 20.3 & 3.32 \\ July & 21.0 & 52 & 2 & 13.5 & 29.0 & 4.72 \\ August & 20.8 & 53 & 2 & 14.9 & 29.0 & 4.56 \\ September & 17.0 & 57 & 2 & 12.2 & 22.2 & 3.06 \\ October & 11.8 & 62 & 2 & 8.8 & 14.5 & 1.57 \\ November & 6.6 & 70 & 2 & 4.5 & 7.7 & 0.71 \\ December & 1.8 & 77 & 2 & 2.0 & 4.8 & 0.44 \\ Average & 10.7 & 64 & 2 & 6.5 & 14.9 & 2.05 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Corum/Center climate/ evapotranspiration (\(ET_{o}\)) data. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Station** **Corum-Merkez** & **Meteorological Data** & **Effect Rain Method USDA S.C. Method** \\ \hline
**Month** & **Rain** & **Effect Rain** \\
**mm** & **mm** & **mm** \\ \hline January & 39.5 & 37.0 \\ February & 30.3 & 28.8 \\ March & 37.8 & 35.5 \\ April & 45.9 & 42.5 \\ May & 60.8 & 54.9 \\ June & 49.2 & 45.3 \\ July & 17.4 & 16.9 \\ August & 11.9 & 11.7 \\ September & 20.3 & 19.6 \\ October & 25.0 & 24.0 \\ November & 30.9 & 29.4 \\ December & 43.4 & 40.4 \\ Total & 412.4 & 386.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Corum/Center rain data.