Answer: Drainage and runoff problems and evaluations are best managed by an on site professional. A drywell is normally used for a small amount of runoff such as that from a gutter, rather than to drain a large area such as yours. In addition to the size of the area contributing to the runoff, the answer to your question would depend on the amount of precipitation you are likely to receive at one time and the types of surfaces covering the area. A landscape architect or someone with a similar level of professional training in grading and runoff management should be able to help you determine what your options are in this instance. I'm sorry I can't be more helpful.
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