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\subsection{Skill Building} \label{subsec:Skill_Building_8}
WEPS currently estimates only one soil map unit in a field at a time.
Therefore, it is recommended that the user select the most erodible soil of a “manageable size”.
This is called the \textbf{Critical Dominant Soil}.
The Critical Dominant Soil is that which typically is the first to blow on the field
and dominate the wind erosion process and is therefore critical for conservation planning. 

The most erodible soil can be considered to be the one with the highest percentage of sand.
For example, a fine sandy loam will be more susceptible to erosion than a loam.
It is important to pay attention to the soils within the field when setting up a WEPS run.
The WEQ (Wind Erosion Equation) \textbf{I factor}
or the \textbf{Wind Erodibility Index} ratings
as shown in \cref{fig:Map showing the soil map units of a field}
may be used to get some idea of the erodibility of the soils.

\subsection{Scenario} \label{subsec:Scenario_8}
Consider the soil map of a field in Grant County, Washington
(\cref{fig:Map showing the soil map units of a field}).
The approximate location coordinates
for the actual field site are: \textbf{46.90713º N, 119.80210º W}.
There are three map units in the semi-circle field.

When determining the Critical Dominant Soil,
the general guideline is to use the \textbf{most erodible} soil
composing \textbf{greater than 10$\%$} of the field
\textbf{or greater than 10 acres} in size (i.e., a manageable size).

\textbf{Question: What soil should be used to estimate the soil loss?}

\textbf{Answer}: From the figures we see that the Royal loamy fine sand (map unit 113)
and Taunton loamy fine sand (map unit 151),
comprise the majority of the field with 77.4$\%$ and 9.4$\%$ respectively of the area.
The Ekrub fine sand (map unit 36) only makes up 13.1$\%$ of the area
(\cref{fig:Map showing the soil map units of a field}).

However, the Ekrub fine sand should be used since it is the Critical Dominant Soil.
It was selected because:
\begin{itemize}
\item {It is the most erodible soil in the field.
It has a Wind Erodibility Index value of 250 and the loamy fine sands only have a value of 134
(\cref{fig:Map showing the soil map units of a field}).
Also, the Ekrub soil has the most sand, which the Wind Erodibility Index is heavily based upon.
It is easy to check the surface sand content for any soil via the WEPS Soil Viewer as a
WEPS in-tool guide for selecting soils without needing to resort to the WebSoilSurvey tool
(\cref{fig:WEPS_Soil_Viewer_Ex8}).}
\item {It comprises more than 10$\%$ of the field.}
\item {It is upwind of the damaging westerly spring winds
(\cref{fig:Wind_Station_Data_table_Ex8}).}
\end{itemize}

\begin{figure}[H]
\centering
	\includegraphics[scale=1.5]{images/Example_8/Ex8-1c.jpg}
\caption{WebSoilSurvey Map showing soil map units of a field. Total field size is 38.9 acres.}
\label{fig:Map showing the soil map units of a field}
\end{figure}

\begin{figure}[H]
\centering
	\includegraphics[scale=1.8]{images/Example_8/SoilViewer_Ex8.jpg}
\caption{WEPS Soil Viewer is useful for determining the surface sand content of the selected soil.}
\label{fig:WEPS_Soil_Viewer_Ex8}
\end{figure}


\begin{figure}[H]
\centering
	\includegraphics[scale=2.0]{images/Example_8/Ex8-1d.jpg}
\caption{WEPS Wind Station Data table showing SW and WSW wind directions dominating in the spring.}
\label{fig:Wind_Station_Data_table_Ex8}
\end{figure}

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