Currently it is just grass covering it. We are having RipRap placed on the front of the dam help with some errosion. Would it be wise to cover the E spillway with riprap also?

I figure it will slow the waterdown, but is that good (less errosion), or bad (water leaving the lake slower)? It also would create some logistical issues for mowing etc.

I concreted my spillway, one of the best decisions I have done with my pond. At times, ill have a foot high water flowing across the spillway. You know texas is getting these 1,000 year floods right now but overall it has made my pond much less worrysome. If you have the funds I would look at putting concrete in and be done with it..

It should only slow the water leaving until the water depth gets above the peaks of the rip-rap. Then water will flow at full rate with no restriction.

Whatever a person does, either concrete, rip-rap or even grass, it is important to have it go up the bank spillway area high enough to account for any eventual potential water flow level.

If a person only has rock lining across the bottom of the overflow area, it will protect fine at normal flow rates. But if excessive flow rates happen where water is above the area where the rocks (or concrete) are covering the soil there could be erosion at that point (on each side of the rip-rap or concrete) and still have dam failure. The lining material has to extend up beyond any point the water depth could potentially get to for full protection.

Also the rock size has to be such that the velocity of water can not wash the rocks down stream. Wider overflow areas with higher flow capacity at lower velocities would be better than narrow overflows with high velocity. Something like concrete that can't move might be a better choice if the only option is a relative narrow overflow area that could see high velocity water flow.

No expert. Just what I see in my minds eye and experience with farm machinery crossings in creeks.

Snrub makes some great points about the sides and how erosion/scouring works.

You also have to consider, if using concrete/riprap, how much height you are adding before water is flowing. If you only have 3' of freeboard to start, and add 6" rip rap, you'll only have 2.5' of effective freeboard before a dam is topped.

Earthen spillways should be as wide and level as possible, divert ALL water AWAY from any excavated portion of the dam, and once sloped for velocity, rip/rapped if needed.

One thing about rip/rap, it creates a VERY turbulent flow that can move some pretty heavy rock in big rain events!

Thanks for the info Rainman. It is a very gentle slope away from the dam, and flows away from the corner at about a 45 degree angle. I think the shrubs would work great at the points. Great idea!!

Have had good luck when using rip rap to cover the rock with chain link fence, chicken wire or something like that. It will keep the rocks in place when the water gets to rolling.
A good turf can take a lot of water when it is established well.

Case in point.....

http://youtu.be/j1kPEMtERSU

I said sNrubs makes some good points...the forum member with a weird ID...NOT sHrubs...lol

I think shrubs on points, would get ripped out pretty quickly if hit by fast flowing water.

Nice video example of the power of water going out an overflow Tbar.

Below are pictures of what I did with some old concrete slabs to counter a problem of my small 2-4" rock being washed off into the ponds as the water increased in velocity as it fell from one elevation down to a lower elevation. I had no problem with the rocks moving on the front side or the middle, just as the water broke over into the next pond. In the pictures at current water levels it would not be an issue. But during last years drought and the pond levels were significantly lower, as the water cascaded down into the next pond, the rocks would wash away.

The concrete slabs were chunks of old concrete sidewalk that went around part of our old 1900's barn. The concrete is older than I am, made of Portland cement and chat (chirt) from local lead/zink mines. Not the best aggregate in the world and no sand so rather poor concrete, but it served its purpose for probably 60 or more years and will serve its second purpose in life in the pond as long as I need it to.

I used the back hoe to make a flat surface to sit on the clay, then hand fitted with a shovel so the old slabs would fit in correctly on the bank. Then filled in any cracks with rocks as big as would fit. It has worked well since last summer when installed.

In the last two two pictures the concrete is mostly covered with water because water is at overflow levels. But you can see the concrete at both sides. This is where water from my tiny pre-sediment pond enters the 1/10th acre sediment pond. The first two pictures are where water enters my main 3 acre pond from the sediment pond. The slabs keep the rock from washing down into the pond. Notice how the ends of the channel are tipped up to make sure the water flow is contained within the channel. If not the water could erode the edges and wash the rocks away at the ends. If the main pond water level is low when this emergency overflow (there is a 6" pipe to handle normal flow rates) the water drops off these concrete slabs into water rather than eroding the bank.

Edit: The last two pictures all you can see of the concrete slabs is the ones on either side of the spillway. But between those slabs and underneath the water are more slabs that would come into play when the water level is much lower in the pond.