What are the major factors that affect drainage patterns?

Answer 1

Water has basically only a couple of ways to leave an area. It can run off and it can penetrate the ground. That leaves the topography, that is, the "shape" of the land as a factor. The land is sloped and will promote runoff, or it is "flatter" and the water can stand on it. Perhaps it's somewhere in between. And there can be loose or crushed rock on the ground that will let water go right through it, or there can be sand, which can pass water fairly well, or there will be some kind of soil, which holds water to a varying degree. That's the second factor to be considered. It's fairly easy to assess the ground to determine its ability to support runoff unless we're talking a graded lot. If a "flat" piece of ground is surveyed, only the boys with a transit and the rest of the tools of the trade of the surveyor will be able to give you a plot of the grade. Rock and sand don't really hold water and will drain it effectively. On the other hand, soils can vary widely in their ability to act as a hydrologic sponge. Additionally, the problem is a 3-dimensional one, and a cross section of the subsurface features over the area of interest will have to be plotted. That involves some cores will have to be pulled from across the site. Land can be graded and shaped to our needs, but this is probably a job for a contractor. He'll have the equipment and the expertise to handle this. Certainly he'll have to work with a surveyor. The surrounds will have provide a place for the water to continue on its way once you have it moving off your land. There are ways to build in subterrainean drainage features, too. Certainly there will have to a place for water to "go" with this scheme, but with perforated piping nestled in sand/gravel and covered with a good layer of soil, there will be no problems with standing water except in the short time right after a heavy downfall of precipitation. All of these options cost, and the idea for the use of the land will have to come together with the availability of financing to determine which method or options will work best in any given application.