Hello all, first time posting here, but I've read and watched the site for several years. I'm looking for some help with strategy for recovering our pond's spillway which is quickly turning into a 20' deep gulley, and avoiding losing our pond entirely.
Here's the background on the issue I'm having:
1 - We built a roughly 2 acre pond in East Texas just over two years ago.
Maximum depth is around 16', average depth is about 7'. We had significant red clay on-site and harvested that for the dam, and the bottom of the pond is red clay. The dam is keyed in 8' below the pond floor, as it was placed on an old logging trail and we had to remove about 8' of compacted logs that had been buried on this spot to get down to clean clay. So, total height of the clay dam is roughly 24' and is approximately 14' across, and ~ 120' long.
There is no drain through the dam, as we wanted to reduce the risk of any long-term weakening of the dam due to the drain.
Our original spillway (see below!) was 16' wide with 14" of freeboard, lined with rip rap. Last summer, it was expanded to 24' wide with 24" of freeboard. It runs pretty much all winter/spring.
2 - We have a lot of drainage into the pond (See attached topo image) - 3 wet weather creeks draining approximately 180 acres met where we build the dam.
3 - We've had two record wet winters since building the pond, and have already had to re-build the spillway last summer after the late spring brought us 9" of rain over 3 days, including a 3" deluge in 1 hour.
The dam was topped, taking about a foot off the backside, we re-enforced the back of the dam, re-constructed the slope, and expanded the spillway to 24' wide, 24" deep, and extended to it about 275' long (see photo attached of the new spillway when it was cleaned up. We added several more trucks of rip rap, it looks like sand - but in the deep summer the dry clay turns into a powdery substance when disturbed, that goes right back into hard red clay when it gets wet.
4 - Our new spillway is gone now!
So, come this winter/spring, we had a much larger spillway. We built check dams out of old logs at the end of the spillway, before it reached the main gulley, and we had solid grass coverage of the spillway (grew through the riprap) as soon as we got it wet.
This winter/spring was even wetter than last winter/spring! It culminated in a 5" deluge last week, and the water found a weak spot in the left side of the spillway, cutting the drainage from a gentle 24' wide area to one about 4' wide near the mouth, and ending up in a 15' deep newly-formed gulley, with toppled trees. The erosion is now about 15' from the mouth of the spillway, and once it hits there the pond will drain quickly by at least 2', and from that point any additional rain will likely cut down to at or below the dam level, draining the entire pond. The photos don't really do it justice, but -all of this- happened in one 24-hour period.
So, my question is this - given the probability of more winters/spring like this, how would you approach this spillway? Should we concrete it ($$!) and then drop a truckload of boulders in the gulley at the drain point, or is there another strategy that may be more cost-effective? We'd really hate to lose this pond, as we've spent a lot on it, and it is a beautiful pond so far.
