First, there is very little paved area in these watersheds. For runoff to occur, rainfall has to be greater than the soil can absorb. If the soils in these areas were very dry before rainfall, they have to be saturated before runoff will occur. In the winter, soils stay moist or are frozen, facilitating runoff. The leaves intercept the rain, allowing it to be evaporated back into the air.
Trees also use more water in summer months, transpiring water back to the air.
In addition to decreasing the amount of water captured, these factors increase the time it takes for water to flow into the Cove. The level response is not as quick in the summer as in the winter. One other thing to remember - the shape of the reservoir is similar to a funnel. This means the storage volume is wider towards the surface than it is at the bottom. The closer the level gets to the top, the more water it takes to see an incremental increase in level.