With reference to the image which you have included in your question, there are two physical factors that might cause the River Turb to flood for the second time this year. The first of these is the heavy and continuous rain that is predicted for the county over the next week. The second factor is the higher than normal amounts of snow melt that are anticipated.
Flooding typically happens when there is too much water for a given river to contain within its banks. When there is too much water, it rises above the banks of the river and spills out, flooding areas that are normally dry. Therefore, we have to ask what two factors are going to cause the River Turb to have too much water for its banks to hold.
The first factor is the heavy rain. As more and more rain falls, more and more water flows into the river. This causes the water level in the river to rise. If it rises high enough, a flood will result.
The second factor is the snow melt. Typically, snow falls in the higher elevations over the winter. That snow melts gradually in the spring as the weather warms. When that happens, rivers rise gradually. However, in this case, it appears that the snow is melting too quickly. This means that more snow melt will be released into the rivers all at once.
When the snow melt is combined with the heavy rain, we have much more water than usual entering the River Turb. Because there is so much excess water, flooding might well occur. Thus, the heavy rain and the excessive snow melt are the two factors that are likely to cause the river to flood.