The dam wall is up and compacted, now it is time to shape the bowl. It is important that you have no steeper than a 3 to 1 grade on the inside of the dam wall. The shore line can be 2 to 1, but I would not recommend anything steeper than 3 to 1 as it makes it difficult to compact unless you use a compactor attached to an excavator arm. If you are adding any soil layers to shape your bowl, make sure you compact every 6 inch layer added.
Wall height achieved
Continued from part 1
8. Get that bowl shaped up and compacted.
Pond ready for bentonite
9. Get you spillway squared away. The spillway should be an area where if the water goes above the freeboard, it can safely exit. This is very IMPORTANT to get right as it will determine your full water level, and it is your safety measure when it starts to overflow. You never want water to flow over the dam wall.
Spillway
Spillway links to swale downslope
10. For us it was time to mix the bentonite in the bowl. We already mixed it in the dam wall as it went up. We spread the appropriate amount of bentonite in the bowl by placing the bags out uniformly in the bowl then simply dumping them out evenly by hand at 3 pounds per square foot.
Recommended Application Amount of Sodium Bentonite
Clay: 1.0-1.5 pounds per square foot
Sandy silt: 2.0-2.5 pounds per square foot
Silty sand: 2.5-3.0 pounds per square foot
Clean sand: 3.5-4.0 pounds per square foot
Rock or gravel: 4.0-5.0 pounds per square foot
11. After the sodium bentonite was spread, we used a rototiller attachment for the skid steer to till it in. This worked really well as we could get up the steep banks easily as it is mounted in the front. Also, we reversed the tines on the slopes to make sure we did not pull the bentonite off the sides down to the bottom as we tilled.
12. Now for the final compaction and this one is EXTREMELY IMPORTANT. Make sure the moisture levels are right and compact the hell out of the bowl. If you have a sheepsfoot compactor, that is great. If not, you can use the wheels of a skid steer, and excavators do have compactor attachments for the arm which are great for steep slopes. Some people do use the tracks of an excavator to compact, but it is less than optimal.