I'm in the planning stages for a new earthen pond on a couple acre property I've recently acquired. The property has a gentle slope, and in one corner has I space I feel may be ideal for a small pond. I'd hoped to make the pond .08 acres (surface area) with a max depth of 10'. Volume at this size is .33 acre-ft.
According to the USDA's 'Ponds, Planning, Design, and Construction' my area would ideally have 12acres of runoff area for each acre-ft of pond. My watershed feeding this pond is only about 2 acres - according to what I've read at least 4 acres would be ideal.
My questions are: 1) In your opinion, would it be better to go with a smaller pond that will hopefully stay more full, or a larger pond that might fill up in the spring but evaporate quite a bit over the summer? 2) Do you know of any other factors that might positively influence this issue I'm seeing regarding less than ideal drainage area feeding the area? I have clay soil which should hold water nicely. 3) Any other thoughts you'd care to share?
I'm attaching a screenshot of my topographic property map with drainage lines specified. My soil profile (unconfirmed at this point.. will test in the spring) is below."
My goal is to have a pond to provide water access and for recreation. This is an off-grid operation.
Thanks and I'm excited to have joined this group! -Chris
[quote] Itasca County, Minnesota 626B—Suomi silt loam, 1 to 8 percent slopes Map Unit Setting National map unit symbol: fcmg Elevation: 980 to 1,310 feet Mean annual precipitation: 20 to 27 inches Mean annual air temperature: 37 to 41 degrees F Frost-free period: 95 to 105 days Farmland classification: All areas are prime farmland Map Unit Composition Suomi and similar soils: 90 percent Minor components: 10 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Suomi Setting Landform: Lake plains Landform position (two-dimensional): Summit, backslope Down-slope shape: Linear Across-slope shape: Linear Parent material: Silty and clayey till Typical profile A - 0 to 3 inches: silt loam E,E/B,Bt - 3 to 36 inches: clay C - 36 to 60 inches: clay Properties and qualities Slope: 1 to 8 percent Depth to restrictive feature: More than 80 inches Drainage class: Moderately well drained Capacity of the most limiting layer to transmit water (Ksat): Very low to moderately low (0.00 to 0.14 in/hr) Depth to water table: About 30 inches Frequency of flooding: None Frequency of ponding: None Calcium carbonate, maximum content: 35 percent Available water supply, 0 to 60 inches: Moderate (about 9.0 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 2e Hydrologic Soil Group: D Ecological site: F057XY020MN - Fine Upland Mesic Hardwood Forest Forage suitability group: Sloping Upland, Acid (G088XN006MN) Other vegetative classification: Sloping Upland, Acid (G088XN006MN) Hydric soil rating: No [/quote
IMO you will enjoy a smaller pond with the correct amount of water compared to a larger pond that is just a shallow mud hole for part of the year. The biggest exception would be if you have some source of supplemental water to top off your pond during dry spells.
It might help a little to "add" some more drainage area for your pond. Since you will have earthmoving equipment on site, you could build a small terrace to capture more of the surface water flows on your property.
(Discussion based on assumption that your pond.PNG is oriented due north.) The runoff from the NE corner of your property is going to go downhill the the west and then turn north and flow off your property past your pond. If you built a terrace along the 1451.5' contour with a berm at your north property line that went up the slope, then that extra water could be routed to your pond.
You might not need to dig the small "bay" at the SE corner of your pond. (Unless you want that bay for some other reason than capturing the surface runoff.)
Your terrace does not need to be at any specific contour, so you can fit it at any location that is pleasing to your eye. Right at the edge of your trees might look nice, but be careful not to route leaf debris into your small pond.
Finally, I think that the USDA handbook is an excellent resource. I believe their calculations for pond size versus watershed are based on average levels of water loss due to seepage AND evaporation. Your Soil Survey results indicate you probably have good clay. If your pond is built and sealed correctly, then you might have less than average water losses due to seepage. That might allow you to "cheat" to a slightly larger than calculated pond size, but I would not cheat too much.
If you spend less money on a smaller pond, that always stays full, then you might be able to do a small expansion later. If you build too big to start, then you have spent more money for a worse pond.
Your berms in blue along the "north" edge will work just fine to capture all of the surface water that moves across your property. They can probably be fairly low and still serve their purpose. (Maybe a little higher as the berm approaches the pond.)
The berms would also be a good place to spoil the material excavated from your pond. Make sure your contractor stockpiles your topsoil, uses the clay from the lowest portions of the pond to construct the berms, and then finishes the berms with your good topsoil.
Using less than 1:3 slopes for pond safety seems strange when you contemplate walking on dry land. However, it can be quite difficult to walk up a slippery slope in a pond, especially for small children or the elderly.
If you will have either (or livestock) around your pond, then I would have one small portion of the pond have a slope of 1:4 or lower as RAH suggests for safety. The rest at 1:3 should help you minimize shallow plants (unless that is what you want).