Todd, the creek survey looks positive.
The Lake was at elevation = 1576.0 last fall – approx 8” low according to Dan Mack.
So the usual Lake is at 1576.7 – or about 1576.5 as a desired Dam height, assuming a 0.2’ deep outflow.
The DNR OHWM was set at 1577.2
That leaves about 0.5’ from the desired pool level to the OHWM – this is the area and depth thus volume; that we will need to have hold the 100 year event without creating a flood level over the OHWM.
The lake bed at the lake outlet is at 1572.9 water elev= 1576.0
The stream bed at the old dam is 1572.5 water elev= 1575.4
The stream bed at the Yamaha road is 1573.0 water elev= 1574.0 road overflow is at 1578.7 – so the road is almost a dam – if the culverts are blocked, but this would impact a larger area.
This indicates that the old dam was more of a restriction to outflow than a water level setting device. I feel this because the old dam appears to have backed up the water to the lake level, about 1.0 to 1.5’ above the water level at the old dam site. Any lake level above this would have gone around the old dam- or thru it or under it. The old dam appears to have been less than 50’ in length.
A new dam would have to be about 300’ long to stop the bypassing- if the 1576.5 level is chosen. The Hydraulic and Hydrology study is the next step to refine the costs and permit implications. The main dam would be less than 50’ for a maximum height of 5’ the side bypass containment dam would be less than 2’ high for 250’ ( about 125’ on either side of the dam. We are preparing a concept cost estimate in the next few days. A lesser height may not help thru drought periods. The DNR may have required releases during drought.
My guess is that for about $50,000 we could have a decent flow restricting dam. Access roads may add $10,000 to $15,000
Permit – Design could add another $25,000
Foundation / soils analysis could add $10,000
So a rough guess is ~$100,000
Maybe a whole new concept to a dam – similar to the old dam – would be possible – so that this is just a flow restriction device – and not truly a dam. Realistically if 5 truck loads of riprap were placed - it would restrict the flow like the old dam – for less than $10,000 BUT getting the DNR to buy into a new concept is difficult.
My elevation analysis leads me to recommend proceeding with the H&H study, as the Dam can be viable to restrict the outflow and to possibly permanently raise the lake pool level to a steady 1576.5 – given adequate rainfall. Drought can always cause a lower water level because of the small drainage area for this lake – it is truly a headwaters lake, with almost no upstream area draining thru the lake.
I’ll send 2 drawings of the creek topo (by separate email. – they show the critical Dam location cross section, and the outlet creek survey data.
From a DNR standpoint it seems feasible, I would like to get a concept review from the DNR, based on our creek topo and survey data. If the H&H shows that we can place the dam at 1576.5 and keep the 100 year storm event from raising the lake to less than the OHWM of 1577.2 – the DNR process is much more stream lined as no taking of land rights is involved.
This will require a slight fee increase of $1000 to $2000 from Northern Environmental. The H& H study could range from $7,500 to $10,000
Please call to discuss.
ESTIMATED project cost breakdown:
- Hydraulic & Hydrology study - engineering & permitting$10,000
- Permit submittal, soils data, engineering plans$20,000
- Construction – riprap restriction$20,000
- Total$50,000
Thanks
Randy M. Lund, PE
Senior Registered Engineer