I do rural land improvement work for a living. My AO is Texas, which is probably not anything like Michigan, but heres what I’d tell a friend or potential customer down here.
The ideal and most cost effective small pond site is one that includes adequate runoff to keep it mostly full in all but droughty times, and with suitable soils to excavate and construct it without importing clay from off site. Unfortunately may times you can’t find that ideal site on a property, especially a smaller property. Keep in mind I’m not talking about small, ornamental landscaping ponds that kept fed from a potable water source. My experience is with real farm/ranch land type ponds.
- Topography of site. Do you have a natural pond location on your property? In other words a location that will maximize drainage area (runoff) into the pond? Is your proposed pond location on relatively flat ground or in a dry creek or draw? I know you mentioned using a windmill to fill it but ideally you’d catch adequate runoff and only use well water to help maintain a full level. As far as depth and size, 10’ deep is a mimimum to be considered permanent water. id design a pond to not be much bigger than watershed into it would support at 10’ or greater depth.
-Suitability of site, mainly Clay content of soil. Soil has to contain enough clay to slow seepage to an acceptable level for an earthen pond to “hold water”. For a small project Soil is typically evaluated with test holes dug with a back hoe or excavator. Do The test holes reveal clay soil beneath your sandy topsoil? If so at what depth and thickness does the clayey soil extend to, what quantities of suitable soil will be present within the excavated area? If There’s any doubt at all about soil suitability, a soil test is well worth the money. The test you’d want in this case determines a soils ”PI”, or plasticity index.
-If soil isn't suitable, often clay can be imported but unless it can be excavated and hauled from very close this can be cost prohibitive. Another option is a synthetic liner, usually made from reinforced poly ethylene. I’ve installed a couple and seen more installed recently here. They can be fairly expensive as well and have pros and cons, but unlike clay blankets and sodium bentonite application synthetic pond liners are guaranteed to hold if installed correctly.
Theres a lot more to look at if you end up building a pond but hopefully this gives you some things to think about before you start discussing your project with contractors. Good luck