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The Emergency Department at Almonte General Hospital...
EnerduResponse Part 2 to Mark Priddle by The Mississippi RiverWatchers

Response Part 2 to Mark Priddle by The Mississippi RiverWatchers

The following is a second part of RiverWatchers’ response to Mark Priddle’s letter as published in The Millstone on April 22, 2013. Our initial response was published on April 30, 2013.

Dear Mr. Priddle,

In your letter you make reference to the construction and operation of the expanded MRPC with the implication that this happened without the degree of scrutiny that is being applied to the Enerdu upgrade. You are right to some degree, but there are many differences. MRPC is tucked away in a corner of Metcalfe Park, they do not store water but operate as a true run-of-river facility, and they do generate revenue for the Town of Mississippi Mills. Enerdu, on the other hand, will be an overbearing addition to the riverfront in the heart of downtown Almonte, they use all of the stretch of the river to Appleton as a reservoir and in the process have damaged, and will continue to damage, the wetlands, and all of the revenue will accrue to its private owner. We have learned that if you do not monitor plans such as Enerdu’s, and protest when necessary, you may end up with something that you will seriously regret in the future.

Although you “do not recall any opposition to it” (the MRPC upgrade) there was in fact a significant amount of feedback to the initial plans. Brad Jones and Judi Agnew, who live on the island near the foot of the lower falls, played a major role in this. One of their contributions was getting a minimum compensation flow written into the MRPC permit to take water. It is common practice at hydro facilities that a portion of the river flow, normally termed ‘the compensation flow’, must by-pass the powerhouse for environmental or aesthetic reasons. The MRPC permit requires that the flow of water to the generators be limited as needed to ensure that at least 2.2 m3/s (cubic metres per second) remains to flow over the dam for 24 hours of every day of the year. They are also required to report every deviation from this required flow. Maintaining that flow and the reporting requirements are taken seriously by MRPC and reports of deviations for 2010, 2011 and 2012 can be found on their website. These show relatively few problems, and they were predominantly short term issues caused by equipment failure, icing conditions or interruption of upstream water flow due to Enerdu operations.

The summer of 2012 was an unusual case in that MRPC was shut down completely from June 15 to the end of the year due to penstock failure. They sent no water through their generators and had no influence at all on the amount of water going over the dam. During this past summer, weather conditions caused particularly low river flows to the point that Enerdu was not able to operate their generators continuously. They would shut down the operation for many hours while the river between Almonte and Appleton filled up behind the flashboards on the weir, and then resume operations until the stored water was used up, followed by further repetitions of this cycle. Numerous spot checks throughout the summer clearly document this. Significantly, during the shut down periods the only water getting to the MRPC dam was the small amount that leaked through the Enerdu flashboards, estimated to be 1 m3/s. That small flow divided between the MRPC dam and the dam on the island near Millfall. The end result was only a trickle remained to go over the MRPC dam.

Your comment “I also note that the nice falls next to the MRPC plant are often completely dry, but I have never heard anyone complain about this” implies that MRPC is at fault in this. As explained above, the culprit is not MRPC, but is Enerdu. In addition, since Enerdu plans to continue this form of peaking operation with their upgrade, The Mississippi RiverWatchers have complained in detail about the inadequate provision for compensation flow in the Enerdu ER (Environmental Report).

In summary, Enerdu proposed a compensation flow of 1 m3/s in their final ER of December 2012. In our response of January 18, 2013 to the ER we stated that this flow was unacceptably low and that they should be following the precedent established by MRPC. Considering the relative lengths of the MRPC dam and the Enerdu weir, the proportionate flow required would be approximately 4.5 m3/s.

In the subsequent reply from Enerdu on January 30, 2013 they acknowledged that the information about compensation flow for MRPC would be considered, but indicated that establishing the compensation flow would be subject to discussions with, and requirements from, regulatory agencies. There was no indication that Almonte residents would be included in those discussions.

We responded to that reply on February 27, 2013 indicating that the essence of their response was dismissive and that it was important that Almonte representatives be included in the negotiations to establish a compensation flow since they would have to live with the results on a long-term basis. No further response has been received.

The following photograph is an example of what the upper falls will look like with a flow of 1 m3/s. This is what we saw most of the time during the summers since 2004.


The following picture was taken on December 14, 2012 when the river flow was sufficient to keep the river level about 3 cm above the flashboards and approximates a flow that would follow the MRPC precedent.


Mr. Priddle, we hope that the above clarifies your issues with respect to MRPC and who really is in control of the water flow, or the lack of it, over the main dam in Almonte. We also hope that you understand better the philosophy that seems to be driving Enerdu in their upgrade plans. Our interpretation is that they feel they own the river and are entitled to use every possible drop of water for power generation regardless of the best interests of Almonte residents. That may sound a bit extreme, but a full reading of relevant extracts from the various communications mentioned will give you a better picture of that apparent philosophy. Unfortunately, it is heavy reading, but we think that you will find it illuminating and useful to digest the extracts that follow.

The extracts do contain a bit of jargon that is explained in advance in this paragraph. Enerdu does not use the term “compensation flow” in the ER, but instead refers to this as minimum flow or residual flow. Enerdu uses the term “By-Pass Reach” for the portion of the river beside the powerhouse and between the weir and tailrace. Enerdu proposes to replace the existing concrete weir and flashboards with Obermeyer gates that include a heavy metal plate that can be raised and lowered pneumatically, effectively a weir with a fully adjustable height. There are four sections of weir proposed, identified as Section A through D. Section A, also termed the canal wall, is a non-adjustable, solid concrete weir with the top at a level of 118.00 masl (metres above sea level), that includes a short controllable spillway. Section A runs between the powerhouse intake and a railway bridge pier. Sections B through D will run above the railway bridge in a segmented curve that connects with the small island on the River Walk. These sections will be equipped with Obermeyer gates. The Mississippi River Water Management Plan specifies the range of water level above the weir that must be followed during normal operations. Specifically, the maximum operational level is 117.70 masl (metres above sea level).

First, some quotations from the Enerdu ER of December 2012:

From the ER (pages 72 – 73)

7.2.1 By-Pass Reach


“As frequently cited by members of the public throughout the public consultation process (see Section 6.2 and Appendix C), the falls downstream of the existing weir are highly valued in the Town of Mississippi Mills for their aesthetic quality. In addition to the placement of the new weir in the footprint of the existing weir (to be discussed further in Section 7.4), a minimum flow will pass over the weir, at weir section C (see drawing G03A in Annex I), to ensure the preservation of the aesthetics of the falls. In certain circumstances (e.g. during typical summer low flows), the provision of minimum flow may not be possible, which is already the case with the existing weir structure.”

From ER Appendix A (page 13)

“It is assumed that a residual flow of 1.0 m3/s will be required to be left in the river (i.e. through/ over the dam for ecological and aesthetic purposes. Based on our initial evaluation of the project, the minimum residual flow currently experienced at the existing facility will not be changed, but will be experienced over a longer period of time.”

From ER Annex I (page 7)

2.2 Hydraulic Model (HEC RAS)

“HEC RAS, a software program designed to model steady and unsteady flow conditions of a given river system, was used to compare the before- and after-construction conditions, average monthly water surface profiles and flow conditions for the Mississippi River to assess engineering and environmental impacts of the different scenarios. The design flow for the new powerhouse is set at 37 m3/s. The existing residual flow of approximately 1.0 m3/s will be maintained. This value was estimated based on site observations during low flow conditions.”

Subsequently we provided Enerdu with our first response of January 18, 2013. The following quotations are extracted from pages 31 – 32 of the Section 4.6 Compensation Flow – Residual Flow

“From the above quotations (from the ER) it is clear that Enerdu is planning to allow a compensation flow of only 1.0 m3/s, and that it will be restricted only to section C of the weir. Furthermore, this very low compensation flow will extend beyond the current summer season, and may not even be possible at times. It must be noted that the present minimum flow of 1.0 m3/s is the result of leakage through the flashboards on the current weir and has no aesthetic value – there is no water cascading over the flashboards and the river is reduced to a rocky canyon with a trickle of water in it.

“This situation must be compared to that of the immediately downstream dam of the Mississippi River Power Corporation (MRPC). Their Water Taking Permit specifies that they will maintain a compensation flow of 2.2 m3/s on a 24/7 basis for the entire year. Furthermore there are strict requirements for reporting any deviations below this level. In the Environmental Report for that facility, simulations reviewed by test groups confirmed that holding the water level above the dam at 2.5 cm above the dam height produced an aesthetically acceptable appearance across the dam face and in the riverbed below the dam, and provide the 2.2 m3/s flow as specified in the Water Taking Permit.

“In view of the fact that Enerdu shares the same stretch of the river with MRPC, in the heart of Almonte, the same standards must apply to Enerdu. Specifically, the top edge of the controllable Obermeyer gates on the weir must at all times be held to a level 2.5 cm. below the surface level of the river as measured above the weir. During periods of low river flow, when the weir height is reduced to its minimum value, the volume of water going through the turbines must be reduced or stopped completely to maintain this 2.5 cm differential. During extreme low flow conditions the compensation flow may be reduced to whatever nature will allow provided that the Obermeyer gates are in their lowest position and the turbines are shut down.

“We note that Enerdu proposes to provide compensation flow (minimum flow) only for section C of the weir. This is not acceptable. The water flow in the by-pass reach is a key feature of the River Walk that runs along the south side of this river section. To maintain a proper aesthetic appearance, all four sections (A through D) of the weir must be operated to maintain a consistent compensation flow as noted above. Section A is a particular problem since it is shown on the drawings as having a height of 118.0 masl except for a short spillway section. This would mean a total lack of flow over most of Section A except during the peak of the spring flood. Since this section is very visible from the lower end of the River Walk, from the Barley Mow restaurant, and from the park behind the Post Office this section in particular needs to be a part of the compensation flow, and its design must include Obermeyer gates similar to the other weir sections.

“Considering the relative lengths of the MRPC dam and the Enerdu weir sections it is estimated that the total compensation flow over the entire weir would amount to approximately 4.5 m3/s with the 2.5 cm level differential. To confirm the best final compensation flow it is recommended that simulations reviewed by a suitable panel of citizen be used, similar to the case of the MRPC compensation flow. It is noted that during a recent period when the river level exceeded the height of the current flashboards by approximately 3 cm. the resulting flow over the weir and down the by-pass reach had a quite satisfactory appearance.

“We note also that there is no mention of compensation flow for the dam at the Thoburn Mill. Presently, leakage through the stop logs and flow over them forms a significant addition to the ambiance of the River Walk. This flow must also be maintained as part of the compensation flow. Again it is recommended that the same 2.5 cm differential between river level and dam height be established using an adjustable Obermeyer gate similar to those on the weir sections.

“A further point related to the proposed residual flow of 1.0 m3/s is that when the generators are shut down, this low flow is not sufficient to maintain the downstream mandatory minimum flow of 2.2 m3/s for the MRPC dam, plus the additional 1.0 m3/s, more or less, that goes over the falls at the Millfall condominium. Observations this past summer showed that there were many occasions when the Enerdu plant was shut down while the storage basin (Reach 18) refilled and only the 1.0 m3/s leakage through the flashboards went to the lower level. At these times the MRPC dam had only a trickle going over it, and Millfall had a similar low flow. This is not acceptable from an aesthetic point of view, and it also puts MRPC in violation of their Water Taking Permit. Our recommendation to establish a 2.5 cm. differential between the adjustable Obermeyer gates and the upstream river level would avoid this problem.

“In summary, the Enerdu approach to compensation flow is unacceptable. We ask you to adopt standards similar to those applied to the MRPC dam, and those standards must be applied to all four weir sections and to the Thoburn Mill dam.”

The Enerdu reply of January 30, 2013 to The Mississippi RiverWatchers’ response of January 18, 2013 contained the following quotations from pages 25 – 26 of the Section 54 Compensation Flow – Residual Flow (RW Section 4.6):

“For clarification, yes, the terms “residual flow” and “minimum flow” used in the ER are synonymous with “compensation flow”.

 “Please see the comments in Section 20 of this letter regarding the information presented in the Project Description (Appendix A of the ER).

 “A minimum flow of 1 m3/s was initially proposed as this was estimated to be the minimum amount of water presently going over the weir/leaking through the flashboards. It is not the final, official, minimum flow that would be passed over the proposed new weir. The final selection of a minimum flow value will be subject to discussions with, and requirements from, regulatory agencies.

 “Thank you for the information you provided on minimum flow releases from the Mississippi River Power Corporation’s (MRPC) dam. Enerdu will consider this information during the selection of a minimum flow.

 “The provision of a minimum flow for only Weir Section C was proposed as water releases from this part of the weir might best maintain the aesthetics of the falls compared to the other weir sections. The alternative option, in which the minimum flow is spread out across weir Sections B through D, will also be considered.

 “See Section 34 of this letter about the height of canal wall (weir Section A).

 “A minimum flow will be passed over the spillway located by the Thoburn Mill condominium. As stated in Section 34, of this letter, Enerdu is in constant communication with the Board of the Thoburn Mill condominium regarding the repairs to the spillway and the provision of flow over this spillway. For future reference, please note that the repairs to the spillway (and by extension, the selection of a minimum flow over this spillway) is not part of this EA, and is being treated as a water management planning issue.”

Section 34 Weir Drawing Issues (RW Section 4.2.15) referred to above contained the following about weir Section A:

“With regards to the canal wall, the engineering work indicated that a height of 118.0 masl would be required for maintaining a proper discharge capacity. However, given the concern over the potential aesthetic impact, Enerdu will verify with the engineering team whether it would be possible to adjust the height of the canal wall without impacting operations at the facility. Note that the purpose of the Obermeyer gate on the other weir sections is to control upstream water levels, an ability that is not required at the canal wall. As a result, the design of the canal wall will likely not be exactly the same as weir Sections B to D.”

Our final response of February 27, 2013 in reply to the above January 30, 2013 reply of Enerdu contained the following quotations from pages 19 – 20 of Section 54 Compensation Flow – Residual Flow (RW Section 4.6)

“The people of Almonte who will have to live with the result of establishing the compensation flow must be included in the negotiations leading to the final result. This cannot be left only to Enerdu discussions with, and requirements from, regulatory agencies.”

Regarding the paragraph from the Enerdu letter starting: “Thank you for the information …”

“This sounds somewhat dismissive. We expect this established precedent for this part of the river to be taken very seriously by Enerdu.”

Regarding the paragraph from the Enerdu letter starting: “The provision of a minimum flow …”

“This also sounds dismissive. The back side of a dry weir is plain ugly and we have seen enough of this in recent summers with the present flash boards. We need to maintain a flow over the falls, and just as importantly, we also need to maintain a cascade of water over all weir sections. Note also that we have previously asked for inclusion of Section A (the canal wall) in the compensation flow. This seems to have been dropped from your consideration, and we ask that it be reinstated.”

Regarding the design of the canal wall section:

“There is no need to have the canal wall at 118.0 masl unless you intend to operate at water levels above the operational maximum level of 117.70 masl. You have also not answered our request to have the top of this wall equipped with an Obermeyer gate to provide for compensate flow.”

Regarding the paragraph from the Enerdu letter starting: “A minimum flow will be passed over the spillway located by the Thoburn Mill …..”

“As stated in Section 38 of this letter, Enerdu has not been in constant communication with the Board of the Thoburn Mill condominium. In addition, as stated in Section 34 of this letter, the repairs to the spillway are a relevant issue for the ER and should have been included in it. The flow over and through this spillway must be a part of the compensation flow agreement.”

Thank you, Mr. Priddle, for having read through to the end of this lengthy response. We hope that you now understand our general concerns with Enerdu’s apparent philosophy, and in particular understand all of our issues with respect to compensation flow.


The Mississippi RiverWatchers



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