Let’s Talk About Dams Part 2

Part 1 of this Blog post visited dams from a sort of historical perspective as well as provided a glimpse of how dams are viewed and permitted from a regulatory perspective, particularly in the Midwest and the State of Illinois.  It really is a “cliff notes” version of that information as a whole and in any case you should reference the embedded links for more in-depth reading or directly consult an expert.

In the second part of this blog discussion article, the focus will shift more to a water quality slant, with how dams can be viewed as an impact and the subsequent trend toward dam removal.  Although there is no question that dams alter the natural flow regimes of rivers and streams, they are also viewed as historical and are revered by some fishermen and the general public.  Removing dams is at times controversial, and many times expensive to a point where there is little incentive for the owner of said dam to go through the process.

Most certainly there is a distinctive difference between dams on already impounded waters (lakes, ponds, and reservoirs) versus rivers and other moving waters.  While many plants and organisms may be found in both habitats, they may prefer one over the other, for example largemouth bass may prefer impounded waters whereas trout may be more partial to river systems.  This is likely to be partially tied to the conditions that may exist in those two particular environments.  The biggest issue associated with dams is the alteration of riverine systems to an impounded state where the internal ecology of the stream starts to function more like a lake in areas of that stream.  This obviously creates an environment where organisms better suited for those habitats begin to better compete and potentially out-compete riverine species.

There is really nowhere better to see an example of this scenario at play than right in our own back yard.  The Fox River south of the Chain O’ Lakes demonstrates many of these very ecological indicators.  While the Fox Waterway Agency (FWA) maintains the Fox River from the Wisconsin border to the Algonquin Dam, other groups have been working hard to study the group while others work as stewards of the river.  One such group, the Fox River Study Group, has worked hard to study the chemistry of the river within Illinois starting below the Chain O’ Lakes down to the Yorkville area.  They have made these very same observations through their studies.  Although these observations have been made, the traction to remove even low-head dams on the Fox River in Illinois has been slow, for many of the same reasons provided earlier in this post.

On the reverse side of the coin is the Des Plaines River which has seen some success in dam removals throughout the past 10 years.  Reports appear to have been good at least from a fishing standpoint.  We have not heard much on the negativity side of things, outside of some navigability with stream speeds and depth in spots.  If that is the worst thing to come from the dam removal process, then it looks like it is well worth it.

Along with the ecological changes that are briefly discussed above, there is a chemical alteration that is tied to changes that take place immediately upstream and downstream of the formal dam structure.  Streams have a natural appetite for sediments; however the downstream fate of the sediment is much different in a stream system that has incurred the installation of structures intended to slow, divert, or impound water.  These structures can serve a source of ultimate deposition and initial source of stream bed scour.  While the day to day function of dams seems harmless enough, the the power of falling water cannot be overstated.  This very premise is relied upon as a viable source of energy to this day.  Now the remaining several thousand dams across the country may have not been instituted for the purpose of hydroelectric generation, but many still have the capability to generate enormous amounts of energy which is released as scour upon the downstream stream bed.  The amount released is dependent upon the elevation of the dam crest and the amount of flow going over the top which can be a function of rain or a scheduled man-made release from upstream or a combination of both.

Immediately upstream of the dam the exact opposite function is occurring.  Water tends to stagnate, leaving a sediment deposition zone.  These zones have limited space of course and over time a sort of baseflow equilibrium is reached with the stream.  Equilibrium can be disrupted at times of high flow as well.  This is caused by the upwelling of materials immediately upstream as water must contract to release over the spillway.  This will create space upstream of the dam where sediment can once again deposit and the cycle repeats itself.

Keep in mind that within a stream, river or any other body of moving water, just like a lake there is ongoing chemical changes taking place constantly.  This does not end at the sediment surface.  Underneath the sediment-water interface there is all kinds of biological and chemical activity.  We often see the results of this activity in both lakes and streams when we see gas released as bubbles to the surface.  Depending on storm surge or seasonal flood flow(s), these constituents can be dislodged en masse, creating pockets of biological oxygen demand (BOD) downstream or make noticeable  water chemistry change detrimental to the existing fish or invertebrate communities.

The above information is of course simplified to make this blog readable.  American Rivers has some great online documentation which discusses these points and further relays the benefits of restoring a riverine community.  On a local basis both the FRSG (link above) and the DuPage River Salt Creek Workgroup (DRSCW) have done independent work on their respective waters.  These workgroups appear to be a preferred model in which Illinois EPA (IEPA) hopes to further address point source pollution.

Based on the materials provided in the IllinoisLakes Blog Part I & II postings, it would appear that there is ample material to support the removal of dams.  The question may further be why is it so hard to remove them?  The process is quite onerous, at least in Illinois it can be.  As of right now the funding to inspect, maintain, and possibly remove a dam all falls on the owner of that dam.  Creative owners may be able to partner on a grant to remove as part of a restoration package, but it does not alleviate them from the formal process of removal initiated by the State of Illinois.  These can include studies of impact which typically cannot be recovered through the typical grant process.  Other states do have revenue sources in place with the sole purpose of assisting in the removal and modification of dams.

This sums up the IllinoisLakes Blog Part 2 take on dams.  We hope you found it informational and enjoyable.  Remember the IllinoisLakes Blog is sponsored by the Illinois Lakes Management Association (ILMA).  If you are interested in lakes like we are please visit our webpage for more information or visit us on Facebook or any one of our numerous public POD sessions.

~p0sted by Admin

 

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