Questions to the MPRB and MCWD Regarding the Minnehaha Creek Regional Trails Project
The Minneapolis Park and Recreation Board (MPRB) and the Minnehaha Creek Watershed District (MCWD) are proposing changes to Minnehaha Creek and the surrounding landscape in South Minneapolis between Cedar Avenue and Zenith Avenue. The following E-mail was sent to them regarding concerns with this project. The MPRB's initial response is shown in red.
I apologize it has taken me a little while to respond to your e-mail. Thank you for your patience.
Many of your concerns around stormwater, flooding, and water management in general have been discussed at multiple CAC meetings throughout the project. In light of some ongoing community conversation, we will provide another summary of that topic at CAC meeting #12 scheduled for Monday night. I wonít therefore address those concerns here. However, your e-mail contains several other questions and comments that I will respond to below, in the body of your e-mail.
Thank you for reaching out to me.
To Adam Arvidson (MPRB) and Tiffany Schauffler (MCWD), /p>
This past week I reviewed the diagrams for the Minnehaha Creek reconfiguration and have some very grave concerns with the plans regarding water management.
It appears that many of the changes have to do with slowing down the water and storing more water in the areas abutting the creek. This seems very counter-intuitive. Currently, nearby homes are having problems with water intrusion which indicates that the area is currently saturated with water. Why would you propose changes to this area that would retain even more water in this area?
The following are some of my questions or concerns:
I see indications that you are going to repair outfalls to Minnehaha Creek. Are these outfalls broken down? If so, when they are repaired, will they increase the quantity of water going into Minnehaha Creek? Also, will there be trash mitigation included in the reconstruction of these outfalls. Many of these outfalls release trash to the creek which ultimately ends up in Lake Hiawatha. Also, who will be responsible for cleaning/maintaining any trash mitigation components?
Trash mitigation will most definitely be included in the guiding principles of the overall document (which will be produced based on CAC recommendation and then released for a formal public comment period). This is also true of the Nokomis-Hiawatha Regional Park Master Plan, which specifically calls for trash mitigation. Exactly how we do that and who is responsible will be determined upon implementation of work.
What does "energy dissipation at the storm water outlet" mean at 5th Ave. S. and the Parkway? What mechanisms are you installing to do this?
At the master plan level, we donít fully design specific elements or treatments. We do know, however, that the 5th Ave stormwater outlet is contributing to erosion on the opposite bank and we should work to solve this issue.
BMP holding ponds
I understand the concept of holding water temporarily during high precipitation events to even out the flow of the creek, but we are seeing this as the only potential solution by everyone who is required to deal with new development, including property developers in Minneapolis. This does not reduce the overall volume of water that Minnehaha Creek and Lake Hiawatha have to handle, which is the ultimate problem. I believe that the creek bed is not only deteriorating from extreme peaks of flow, but also from the ever constant high flow of water that it is asked to handle. Unless the total volume of water is reduced, you are not solving the problem. So, I don't see these holding ponds as a solution to much of anything, other than catching some sand that needs to be dredged out periodically. And, I see them as adding more water retention in neighborhoods that are already saturated.
I do have 2 specific issues with the 'BMP' proposed at Cedar Ave. and 48th St. Your diagram shows that you are taking out 48th street just west of Cedar Avenue to put in a holding pond. This street is used by many people to access the gas station without having to deal with the traffic on Cedar Ave. In particular, people who need to travel north from the gas station use this street to exit the gas station, going then to 18th Ave. to travel north. This is because it is impossible to go north on Cedar Ave. from the gas station. And, with the Bergan's development across the street (adding 125 more vehicles), Cedar Avenue is only going to get worse. You will be forcing these people to turn right onto Cedar Avenue and use the Parkway. 48th Avenue serves a vital function for this neighborhood. My second issue is concern over putting a pond right next to this gas station which has underground gasoline tanks. This seems to be a dangerous situation, especially considering the problem that occured with the kinked gas line by the ponds at the Lake Nokomis lagoon; we believe that the Lake Nokomis problem was due to the heightened water table from the ponds you put in. I think that it is very unwise to place any new water features near gas lines or gasoline tanks.
I question the use of the term BMP (Best Management Practice) for these ponds. A pond, in and of itself, is not a BMP. A BMP is a practice, or set of practices, that reduce pollution when implemented in the appropriate setting or situation. In my opinion, these implementations do not qualify as a BMP because they are inappropriate for this setting or situation.
I see you raising two topics/concerns in this section: one with the idea of BMPs and the other a transportation related concern with elimination of the small frontage road. I will address the second topic here. There has been significant conversation in our community engagement about that frontage road and most folks support its removal. Though we understand some use this park road to access the gas station, MPRB is essentially operating duplicate infrastructure here, and maintaining a redundant paved surface that contributes to stormwater runoff. The proximity of the frontage road/Cedar intersection to the Parkway/Cedar intersection also creates confusing and potentially dangerous traffic conditions.
Remeandering of Minnehaha Creek
I see many places on the diagram where you are indicating that you are going to create meanders in Minnehaha Creek that don't currently exist. I have repeatedly heard from both of your organizations that this is to slow down the water flow so that more water can absorb. These areas are currently saturated with water to the point that it is flooding homes. To me, this seems to be exactly the opposite of what needs to be done. You need to evacuate the water more quickly and/or mitigate the flow into this area. I believe that remeandering of the creek is a waste of money.
I also see that you are going to rebuild the bridge at 4th Ave. S. to accomodate your remeandering of the creek? If the bridge is in need of repair, this might be a reasonable project. Otherwise, it appears to be a waste of money.
A master plan is a long term vision for the park. The 4th Ave/50th Street bridge may not be in need of repair now, but it is problematic both from an ecological and ped/bike transportation standpoint. The master plan is suggesting its modification when appropriate.
I see 2 places where you indicate that you will have a braided stream. I am assuming that this is not present today and you are proposing to build this? If so, why? What is the purpose? My research about natural braided streams says that they are created when the flow speed of the creek/river is insufficient to carry suspended soil, so the soil drops out and settles in the creek bed. Unless you are going to substantially lessen the amount of water going down the creek, which currently has an extremely high flow rate, I don't see how you will maintain this feature as the soil will be washed away.
I see one feature for 3 cascading ponds. Is there a functional use for these ponds, or is it just decorative? Please explain what the functional use is, if there is one.
The cascading ponds would replace a concrete flume that sends street runoff into the creek down a steep slope. The elevation change between street and creek is significant. The cascading ponds are a response to managing stormwater treatment on a steep slope.
Increase in 100 year flood plain
I see 2 areas where you show that the 100 year flood plain is expected to increase dramatically in the next 30 years. This gives me the most concern. If the flood plain is going to increase, this says to me that this area is unable to handle the increased precipitation that is expected to occur. Therefore, if these areas are to be salvaged, something needs to be done to make sure that the level of water entering this area does not increase over time. This means that the additional precipitation that is expected due to climate change must be mitigated elsewhere. The main place that this can be done effectively is in the upper watershed; the upper watershed needs to retain its share of the increased precipitation. If this is not done, these 2 areas in South Minneapolis are dead meat. There is no way that they will be able to handle their own increase in precipitation AND what is dumped on them from the upper watershed.
As has been discussed with respect to the Hiawatha Golf Course, putting constructed wetlands in high flow areas and flood plains is not recommended by the EPA. Nor, do you put them near other properties. These constructed wetlands would, basically, widen the current creek bed, thus bringing the water even closer to the neighborhood infrastructure that is suffering from water intrusion.
Have you verified the levels of basements in the low-lying areas to determine the affect on the water table under these homes like was done for the Hiawatha Golf Course project?
Putting in these water features in an area that is already saturated with water will do little more than make the water problem worse, as we have seen at the Lake Nokomis lagoon. You haven't figured out how to deal with the problems at Lake Nokomis, yet, you are proposing to do more?
How is all of this water going to be controlled for release? WIll there be outlet controls on these new water features (ponds) that can be used to allow or disallow release of water so that all is not released at the same time? Or, is this a natural release; when they fill up, the excess water will flow into the creek. Everyone is talking about storing and releasing later, but I haven't heard anything about controlling the release of this water. So, what controls will be on these new water features to manage the release of water?
Do you have information about the maximum amount of water MInnehaha Creek and Lake Hiawatha can handle to keep the creek, lake and neighborhoods healthy? Any changes in the watershed should be based off of this information. Right now Minnehaha Creek and Lake Hiawatha are expected to handle much more water than they were ever designed to handle. They should not be required to handle any more water than a healthy baseline. If I were an engineer in charge of this area, I would base my decisions on the following premises:
First step: Determine the maximum amount of water that can be handled by Minnehaha Creek and Lake Hiawatha (the exit mechanism) without negative effects to these bodies of water and their surrounding communities. Also, determine the maximum amount of water that can be handled by other bodies of water that feed water into the exit mechanism without negative effects to those bodies of water and their neighboring communities.
Step 2: Determine how much water is currently being contributed by each source (lake, creek, community), and also how much will be contributed in the future based on impending climate change
Step 3: With these 2 sets of information, you can now make equitable determinations regarding how much each source can contribute to the creek and how much each source must mitigate (retain) in their area.
Step 4: Each community then needs to look at solutions that mitigate the excess water that they can no longer send into the exit mechanism (Minnehaha Creek and Lake Hiawatha). The ultimate goal of this is to establish requirements that communities will abide by to make sure that the maximum amount of water that can be handled by the exit mechanism is not exceeded. This ensures that all communities in the watershed contribute to the solution, that all communities in the watershed are protected in an equitable manner, and no one community suffers at the expense of another.
What is the projected cost of this project?
A full cost estimate of the master plan, outlined project-by-project, will be included in the master plan document that will go out for public comment.
I would appreciate your response to my questions and concerns, as expressed above.
Plus, we, as a community, have asked for a comprehensive approach to and study of the Minnehaha Creek Watershed before changes are made within the neighborhoods in the lower watershed that are currently suffering from the recurring water problems.