PLIA President Tom Duffy recently spoke with Corey Clark, Chief Engineer of the Dam Bureau, NH DES. Here is what he learned about Dollof Dam and its repairs: Dolloff Dam has been under study from 2020, when leakage under and through the dam was discovered. Monitor “test” wells were installed to determine the cause and amount of the leakage more accurately. When water was raised to “full pond”, wells showed higher leakage. When the lake was lowered, test wells showed less leakage, demonstrating that water has been seeping through the dam. The dam bureau also noted gaps in the large blocks on the water side of the dam. The immediate plan is to lower the lake down the full 7 feet that is possible at the dam. This will expose gaps in the blocks on the lake side of the dam to allow them to be patched with concrete. It is estimated that ALL THIS WORK SHOULD BE COMPLETED BY the end of the first week of April if they are able to start work by April 1. This is contingent on getting the lake sufficiently lowered by that time. Boards will then be put back into the dam and the test wells will be monitored as the lake refills. Based on the data from the test wells, the dam bureau will determine if the leakage has been decreased and if the sink hole is growing or is stabilized. At some point this spring, divers will check the bottom of the dam from the lake side for additional gaps and suspicious areas. A second monitoring station is measuring the leakage from the bottom of the dam where there is a sealed door acting as a plug at the very bottom of the dam. There are monitoring “weirs” there and data is collected hourly to determine the amount of leakage from this area and to see if the leakage increases as the lake fills. In addition to this immediate work on Dolloff Dam, be aware that 4 locations on Pawtuckaway are under review by the NH DES for more extensive renovation. Those locations are the two dams on the lake, Dolloff and Drowns, and the two dikes, Gove Dike and Drowns Dike. At some, as yet undetermined time in the future, the dams and dikes may be subject to major repair and large, perhaps total, drawdown of the lake may be necessary. |
Author: Neil Santos
Doloff Dam Repairs May Be Needed, Lake to be Lowered Two Feet
On Monday this week (March17) the NH Department of Environmental Services observed a sinkhole on the crest of Dolloff Dam on Pawtuckaway Lake. A small depression was observed in the vicinity of the sinkhole last year but over the course of the winter this depression appears to have developed into a sinkhole. A sinkhole can be a significant issue on any dam and warrants immediate investigation. A sinkhole in a dam is primarily caused by water running through the soil material in the dam and that water eroding the internal dam material. If left unchecked, this could lead to increasing erosion and loss of the structural stability of the dam.
In the case of Dolloff Dam, leakage has been historically observed on the downstream side of the dam in the area of the sinkhole, however, this leakage has never been associated with internal erosion. While NHDES does not feel that the stability of Dolloff Dam is of concern at this point in time, more investigation is necessary to determine if that leakage is creating a situation where material is being moved from within the dam.
During a site visit on Tuesday (March 18), several voids were observed in the concrete on the upstream side of the dam which may be leading to water flow through the dam. NHDES will be lowering Pawtuckaway Lake, possibly as much as to the historic winter drawdown elevation of seven feet, so that these voids can be filled with cement. While this will help with the situation, NHDES does not believe that this will solve the issue.
The lowering of Pawtuckaway Lake will occur with the use of the discharge mechanisms at Dolloff and Drowns Dam and will likely take one to two weeks. At that point, NHDES will mobilize to repair the concrete which will take approximately one week. Once repairs are completed, and further investigation is conducted, NHDES intends on starting to refill Pawtuckaway Lake to the full summer elevation. However, if further investigation reveals that there is a risk of further sinkhole development if the impoundment is increased, then NHDES may have to keep the impoundment at its lowered elevation. As many of you know, NHDES is currently working with an engineering consultant to review the deficiencies of all four Pawtuckaway Lake Dams and to come up with an overall rehabilitation design for all four structures. NHDES will be working with that consultant to perform further investigations, such as diving and camera work, to prepare a plan for refilling Pawtuckaway Lake.
Thanks to Corey for keeping us in the loop!
Milfoil Efforts on Powwow Pond
Powwow Pond is a 348 acre body of water in Kingston. They have had significant issues in controlling variable milfoil. This article from the Derry News details their attempts to manage this problem.
More Repair Work on Mendums Pond Dam
(Ed Note: When water needs to be released to increase the flow in the Lamprey River System, the dam is opened alternately in Pawtuckaway Lake and Mendums Pond. When water from Mendums Pond is not available, as in this drawdown, all the needed water must come from Pawtuckaway Lake)
In 2015, Mendums Pond was drawn down 20 feet below full lake so that major repairs could be made to the Mendums Dam. This repair took over a year to complete and Mendums did not reach full lake level until 2017. You can read the NH DES bulletin about that activity here.
Despite that major rebuild, in 2014, the dam bureau felt that more major work needed to be done and the lake was again drawn down 20 feet in the fall of 2024. Here is a quote from the NH DES Dam Bureau website.
“Mendums Pond Dam in Nottingham will have a deep drawdown this fall for reconstruction of the downstream part of the dam. The project is split into 3 phases and when each phase is completed, the pond may be filled incrementally. Worst case scenario for 2025 will be the pond at complete drawdown and best-case scenario is to gain some pond through the summer and fall. Variables such as weather, availability and timing of subcontractors, etc. can impact the schedule and is challenging to forecast”
Cyanobacteria Problem on Lake Kanasatka
Lake Kanasatka, in Moultonborough, has had a serious issues with phosphorus loading and the resulting cyanobacteria blooms for several years. In 2023, for example, a cyanobacteria warning was issued by the state that lasted from late summer through the fall, 121 days in total.
The following articles detail the issues facing that lake and the costly solution to solution to that problem. (Ed Note: Even with this treatment, Kanasatka continued to have cyanobacteria blooms last year, although with a much diminished duration.)
Restoring Lake Kanasatka FAQ Bulletin
Alum Treatment on Lake Kanasatka has successfully eliminated Cyanobacteria Blooms
Lake Kanasatka Feted for Reversing Cyanobacteria
Enfield Adopts New Septic Rules for Waterfront Property
The Enfield NH Selectboard recently adopted new septic regulations for waterfront property in the town that require septic inspections every six years and pump-out every three years to reduce the inflow of phosporus into the town’s waterbodies.
Understanding Warrant Article 18
The Town will be asking for a loan from the State to fund a watershed study for Pawtuckaway Lake but the loan principal will be forgiven when the watershed study is finished so the Town will not owe any money. All the interest that accrues during the term of the loan will be paid for by the PLIA.
Read the following paragraphs for additional information.
What Does it Mean?
The Warrant Article, if passed, allows the Town to apply for a Clean Water State Revolving Fund loan. The funds will ultimately be used to pay for an updated watershed plan for Pawtuckaway Lake. Even though the loan, if granted, will have the principal ultimately forgiven, state law requires that the Town must have the authority and ability to repay as if the loan were not going to be repaid. That is the reason why the Warrant Article mentions that the Town would be authorized to issue bonds to repay the principal of the loan even though it would not be needed in this case. The Warrant Article also states that the PLIA will pay any and all interest on the loan. It is estimated that the total interest would be around $1500-$2000. It also mentions, in addition to doing the watershed plan, the possibility of doing some mitigation actions. If done, these would be quite small activities, more in the nature of feasibility studies than the relatively major mitigation activities that might be specified in the watershed plan.
What is it For?
The PLIA would like to update our watershed plan which was last updated in 2008. While a watershed plan has many parts, in essence its purpose is to determine the factors which affect the health of a water body and recommend mitigation actions to improve it. While we have several reasons for wanting this update, the primary reason is to determine the factors which are leading to an increasing level of phosphrous in our lake. While any excess nutrients in the lake are a problem, phosphorous in particular, can lead to bigger and more frequent cyanobacteria blooms. We had two such blooms last summer leading to recommendations to stay out of the lake for periods of time since they can cause serious illness and possibly even death. With an updated plan we can understand the most effective mitigation actions and actually get a start on the major mitigation work.
Why a Loan?
Developing watershed plans is a complex activity and requires hiring experts to do the work in conjunction with information from local residents. The cost to update our plan is estimated to be between 65K and 100K. We hope to get the necessary funding from a federal program, the Clean Water State Revolving Fund (CWSRF), which is administered separately by each state. In NH these loans have to be given to a town rather than a lake association or other non-governmental body.
How Does it Work?
As stated above, the way NH administers the program is to provide the loan to towns. These loans are like lines of credit in that interest accrues only as the money is requested by the town. When the purpose for the loan, namely an updated watershed plan, is complete, the Town informs the State that the loan should be closed. Having fulfilled the loan purpose, the State then forgives the principal. The net result is that the only thing that is owed to the State is the interest on the loan.
Summary
The Town will be asking for the money directly but the PLIA in consultation with the Town will engage a consultant to actually perform the work. The key here is that the Town is required by the terms of the loan program to be the middle man but the Town incurs no financial obligation other than a tiny amount of administrative work. Of course, none of this is a guarantee that we will qualify for the loan even if approved by the town voters. If the Warrant Article is approved, we will work with the Town to provide a pre-application to the State by May 31st. After a vetting process to determine loan candidates, the actual loan applications are due in the fall.
PLIA Seeks Grant to Reduce Cyanobacteria Threat to Lake
Cynaobacteria blooms are increasing in many New Hampshire lakes and our lake is no exception. Last year we had at least two such blooms that were verified by NH DES, one almost impacting the busy July 4th week. In 2023, Lake Kanasatka had a bloom that lasted 121 days, effectively shutting down lake activities for most of the summer and into the fall. Cyanobacteria can cause serious health issues and even deaths in rare cases. They are caused by several factors, most notably increasing phosphorous levels and rising average lake temperatures due to climate change. Phosphorous enters the lake primarily from water runoff from the land. This phosphorus loading is increased by actions such as fertilizing lawns, cutting down shoreland vegetation, using impervious surface materials, and not controlling erosion.
The PLIA is concerned about the increasing phosphorous levels in the lake and is working with DES, state and town officials to apply for grants to update our watershed plan. Our most recent plan was developed in 2008 and there have been many changes to the lake since then. The PLIA applied for a so-called “604B” grant last fall but we were not successful. This spring we intend to apply for a Clean Water State Revolving Fund grant from NH DES. If we do get the grant, we plan to engage a contractor to update our watershed plan. The plan will cost around $70K and will take at least a year to produce. With a new plan in hand, we will be able to request additional grants to perform mitigation projects to reduce incoming phosphorous and, we hope, lessen the potential for future cyanobacteria blooms.
All lake resident can also help in this effort by reducing property runoff, eliminating the use of fertilizers, making sure their septic tanks are functioning well, and protecting shoreline vegetation.
PLIA now has an Instagram account!
A picture is worth a thousand words. Our members have a history of taking great pictures of wildlife, scenery and lake activities which can be seen in our Photo Gallery. Instagram is another great platform which allows us to easily capture images, videos, and stories to share Pawtuckaway Lake with the world. Please follow our new Instagram account to stay in touch with PLIA activities and to see beautiful images of the lake from our members and fellow lake lovers.
You can now follow the PLIA on Instagram @Pawtuckawaylake_PLIA
Please feel free to tag @pawtuckawaylake_plia in your lake pictures or share them via a direct message if you would like them to be featured on the PLIA page.
2020 Annual Meeting Recap
For those of you who missed the 2020 Annual Meeting held live via Zoom on July 25th, 2020 or attended but were not able to re-join after the “technical difficulties”, the recordings of the presentation are available for your viewing below.
