By Steve Deyarmond Steve@SandyPines.com
We drive across the Dam many times each summer without any thought regarding the age, condition, or safety of the Dam. We do not even mention or talk about it much. It is just there holding the water that provides the lake that we enjoy and recreate upon. Have you ever thought about what would constitute a lake level emergency, a potential Dam failure and at what elevation level and how that is determined or observed?
The Dam and lake are both important assets to our community and maybe one of the largest liabilities. Built in 1971-1972 our dam is 50 years old. Most Dam safety experts indicate that corrugated pipe (utilized in our Dam construction) has a life expectancy of 25 to 50 years. In the last few years, we have replaced the gate valves and every three years an inspection of the Dam occurs. Working gate valves provide the means to release water and maintain a safe lake level.
Lake Monterey Lake Dam is considered a High Hazard Dam. Determination of a High hazard Dam is not made because of the condition of the Dam but by the potential for loss of life, injury or damage that would happen if the Dam failed. We also must think of upstream loss of property values, loss of recreation, damage to watercraft, docking systems and the habitat. A good source to look at upstream damage is to google Edenville Dam pictures.
Last fall maintenance was completed on the downstream side of the Dam of cleaning brush, opening ditches, and reviewing the toe drain to drain water. With the age of the Dam any water
flow or seepage is a concern on the downstream side of the Dam. We did have some areas that appeared to be waterflows/springs on the downstream side. All Dams have seepage. We did have an engineer observe the flow and provide opinion on the observations of flow. Fast forward to this spring and it appears that the water seepage was from runoff as the engineer suspected as those areas do not have seepage.
Our Dam is an earthen Dam which is very common. The core of the Dam is Clay and approx. 600’ in length. The common elevation of lake Monterey is 672’ and water flows over the spillway at a lake elevation of 673’. The crest of the Dam is at an elevation of 677’. Water elevation of 675’ would be a declared emergency as it would be within 2’ of the crest or top of the Dam. This is 6” above the trash rack of the spillway at the Dam. Understand that to open the gates (12” and 30”) of the spillway a maintenance person must stand on top of the trash rack. The Water from Lake Monterey flows into Pigeon Creek and then into the Rabbit River. Should the Dam fail it would flood Lake Monterey Golf course then the residents along Pigeon Creek and Rabbit River residents downstream.
Engineer reports indicate that it is unlikely that the Dam will fail by flowing over the crest of the Dam (677’ elevation) as water will traverse across land on the north shoreline about 1,400’ from the Dam when the elevation of the lake is at 675.1’. That would place this overland overflow from the lake east of Okemos Trail near the shuffleboard courts. Regardless of what we think is unlikely nature always has it way in causing natural disasters. Many things can go wrong with Dams. Some things are slow and gradual, and others are unexpected. Heavy downpours, extended periods of heavy rains, high water levels, saturated soils, seismic activity all have a role in potential disasters. Even burrowing animals can influence the condition of a Dam.
Sandy Pines has an emergency Action Plan for the Dam which is broken down into three commonly used emergency levels. A level 1 emergency which is issued when the failure of the Dam is imminent. Level 2 in which the Dam has potential for failure and Level 3 which is a non-failure emergency.
Priorities during potential or imminent failure of the Dam are Public Safety or Human life, protection of downstream property and protection of the Dam.
In an emergency (Level 1 or 2) local and state officials would be contacted, downstream residents would be contacted and or evacuated, pre-selected contractors would be contacted to resolve the issue, the membership would receive a RAVE alert, the Dam would be closed to traffic, boating on the lake would cease, Allegan County Road Commission would close, and barricade roadways effected.
In 1997 a heavy rain event caused much flooding, caused roadways to be floods and some roads impassable. The overflow or spillway for Lake Monterey was like a geyser from the overflow of water. 30th Street near the Rabbit River was flooded and pavement damaged. 26th Street north of 138th Ave was flooded and pavement damaged. During heavy flood events, water over roads and damaged roadways the safest solution may be to remain at Sandy Pines until the water recedes and damaged roads are visible and passable.
If you have been at Sandy Pines for numerous years you may have noticed that the cement on the upstream side of the Dam has become cracked and sunken. What once was a sharp angle to the water’s edge has become indented to the water’s edge. Or you may have not noticed as this is a slow process that has occurred over the years. The upstream side of the dam is commonly the means to protect the Dam from wave erosion and ice action. The concern is always a concern of piping or flow of water through or under the dam. The concern of safety for persons fishing off the Dam with uneven surfaces is also a concern. Eventually the upstream side will need to be repaired. Whether this is a completely different approach to correct or pumping cement under the existing upstream Dam face will be determined in the future.
As a Dam owner we do have the responsibility and obligation to maintain the Dam. Many Dam failures are a result of failure to maintain claiming that the organization did not have the funds to maintain. Consideration in the future will have to involve lining or replacing the corrugated pipe under the Dam, cleaning or replacing the toe drain on the downstream side of the Dam and fixing, replacing, or correcting the upstream side of the Dam’s cement face.