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THOMAS HARDY, the Meadow Center’s chief science officer, says there is ‘no credible scientific evidence’ that removing Cape’s Dam will harm wildlife in the San Marcos River as dramatically asserted this week by a UT-Austin biologist 

September 18th, 2015
Commentary: Don’t let professor’s sloppy work obscure the facts about Cape’s Dam removal


I can understand Dr. Molly Cummings’ desire to advocate for turning Cape’s Dam into another series of manmade rapids similar to Rio Vista Falls, the vision of Mr. Ben Kvanli and the kayaking community. Cummings is, after all, a former member of the U.S. Women’s Kayak Polo team, something she failed to disclose in a recent opinion piece in which she suggests science supports that aim.

But as a biology professor at Texas State University who actually studies the ecology of the San Marcos River, I am compelled to clarify where those opinions are unsupported by science-based facts.

Cummings does offers sound advice to the San Marcos City Council when she admonishes them to “depend not only on analyses by hydro-geologists, but also biologists like me [Cummings] who study local aquatic fauna and their specific habitat needs.” I have studied the impacts of dams on aquatic plants and animals in rivers for more than 30 years and specifically in the San Marcos River ecosystem for more than 15 years. I am Texas State’s Meadows Endowed Professor of Environmental Flows. I am not, nor have I ever claimed to be, a hydro-geologist as suggested by Dr. Cummings.

The San Marcos City Council and San Marcos residents deserve the truth. Here it is:

Dr. Cummings says, “This section of the river above the dam is critical for habitat protection, as the downstream sections are unsuitable due to pollution from a Superfund site and fish hatchery.”

In fact, publicly available data from the Texas Commission on Environmental Quality show that surface water samples taken downstream from the Superfund site have never found actionable levels of contamination in the river.

In addition, fish in this area have been tested and certified as being fit for human consumption. A study of aquatic insects upstream and downstream of the AE Woods Fish Hatchery by Loraine Fries and D.E. Bowles in 2011 concluded that, “benthic macroinvertebrates likewise showed no appreciable differences between upstream and downstream sampling locations, and upstream and downstream communities overlapped considerably in terms of species composition, species richness, and functional feeding group composition.”

Extensive sampling by Kenneth Behen in 2013 found 28 species of fish in both this ‘unsuitable’ section of river and in free flowing river sections below Spring Lake Dam. In addition, there are similar fish densities in both sections of the river and, in fact, this downstream section of the river below Cape’s Dam currently supports a viable sport fishery and presence of the endangered fountain darter.

Dr. Cummings says, “If the weir is destroyed, it will greatly reduce the number of plants and small fish species that can’t withstand high flow rates, and this will have dire consequences for the entire fish population here, including those that Texas’ sport fishers rely on.”

The removal of Cape’s Dam will restore natural higher-velocity flow conditions to this section of the river, but there is no evidence to support the notion that a great reduction in the number of fish will occur. Annual monitoring data collected by the Edwards Aquifer Authority since 2002, the San Marcos Observing System and Behen’s research results in 2013 clearly show that sections of the San Marcos River that are not influenced by Rio Vista or Cape’s Dam have large populations of small fish species, sustain a biodiverse fish community and provide plentiful habitat for young and juvenile fish to thrive — including the endangered fountain darter.

There is no evidence to support the notion that a great reduction in the number of plants will occur, although I do expect an increase in the number of more velocity-tolerant species. Why? As detailed in a study soon to be published, my colleagues and I found significantly increased total area of the endangered Texas wild rice as well as other native aquatic plant species restored to areas of faster water habitats of the San Marcos River where non-native plants have been removed since 2012.

To suggest that Cape’s Dam ‘weir’ is a beneficial feature necessary to maintain biodiversity in the San Marcos River ignores all the available data on fish and habitat characteristics in the San Marcos River. It also ignores decades of published literature that clearly shows that weirs and low head dams cause habitat fragmentation and loss of native biodiversity while promoting expansion of introduced non-native species. The San Marcos gambusia is extinct because of factors that include habitat alterations like dams and weirs and the introduction of non-native species like the Amazon and Sailfin mollies that thrive in the artificial slack water areas around dams and weirs.

Those of us who have actually studied the San Marcos River know that the Superfund site has no demonstrable impact on the flora or fauna of the San Marcos River and that the river downstream of Cape’s Dam and the AE Woods Fish Hatchery contains the endangered fountain darter and a healthy diverse aquatic community.

Removal of the dam is the most ecologically sound step to take for protection and recovery of endangered plants and wildlife in the river. Let’s be clear: There’s no credible science to support Cummings’ contention that weirs are essential to the biodiversity of Texas rivers.

Texas State University biology professor THOM HARDY is the chief science officer at the San Marcos-based Meadows Center for Water and the Environment. In a study commissioned by the city of San Marcos, Hardy recommends removing, rather than rebuilding, flood-damaged Cape’s Dam.

COVER: Local children revel in the San Marcos River at Stokes Park where an old mill race rejoins the river’s main channel in late summer 2012. Cape’s Dam upstream of this location is the subject of a contentious fight over whether to rebuild or remove the flood-damaged structure. MERCURY FILE PHOTO by JAMIE MALDONADO

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13 thoughts on “Commentary: Don’t let professor’s sloppy work obscure the facts about Cape’s Dam removal

  1. So maybe we need to pull out the dam by Saltgrass. Empty Spring Lake. Can I get an amen? #alldamsmatter

  2. They wouldn’t ever remove the spring lake dam by Salt Grass because that is basically a private laboratory for Texas State Professors. The only real reason for the proposed removal of the dam is to limit recreation in the area. The area is currently great for swimming and removal of the dam would make the area far less appealing to the college students moving into those apartment complexes. They keep mentioning that Texas Wild Rice will grow better in this area due to the increase water velocity but they don’t seem to account for the overhead canopy and the limited direct sunlight. Based on where you find the majority of the wild rice it seems to needs direct sunlight to flourish and that area doesn’t have a lot of direct sunlight.

  3. just get the bulldozers, back hoes and sledge hammers in ther and get rid of all the concrete, walls, damns, metal, asphaut, pavement, sidealk and roads, and start fresh. it is completely destroy atm and should be fixed post haste.

  4. Thomas Hardy is a little sensitive. Because the UT professor kayaks, she must be biased. To dismiss an opinion based upon this is as dumb as dismissing Hardy’s opinion because he likely celebrates Earth Day. Everyone has a bias, most of all Hardy.

    The problem with this debate is that we only hear from the two extremes — the Hardys who feel human activity is a stain on the far more important rice plants, and the other extreme who wants to turn this area into a tricked out water park. For what it is worth, I think the dam is as historic as any other structure in San Marcos. Kids and adults have enjoyed those islands and recreation in the area for more than a hundred years. I would like to see any repairs preserve for us the ability to enjoy those islands for one hundred more. But no matter what, I’d prefer to disempower the Meadows Center and folks like Hardy from fencing off the whole river and taking it away from the folks who live here. People > Rice.

  5. It’s river front park and should be exploited as such. Rio Vista is stressed to the max. Don’t rush into anything but begin planning to allow all the citizens to use it – figure out parking, access points, etc. Lion’s Club float is too short – use this park to make the float longer. More picnic tables.

  6. I wish all of you arguing about public access to Thompsons island and stress on Rio Vista had been present and fighting for a park at Capes Camp instead of an apartment complex. Too late now! Yes, we have a park, but with almost no public parking access. Where in the world would we put bus pick ups for the Lions Club? And yet, because of several oversights in the PDD, the apartment dwellers have full access to essentially a “private” riverfront park. That’s even how the apartments are marketed “your access to the San Marcos River, #floathome”.

  7. I’m not a professor, just a citizen of San Marcos observing the debate about Capes dam. To me, it looks like The rice grass habitats look out of control through out the San Marcos river area with their signs and roped off areas. Years ago they use to cut down the rice grass with a machine from Aquarena. This did not stop the rice from growing. Sewell Park looks terrible with the rice grass sticking up every where, not a place I’d want to swim in any more. I believe the river flow will be endangered due to the rice grass eventually clogging the flow. Let’s work together as a community to provide access to our river for the people to enjoy and respect. When is there enough rice grass areas? Please repair the Cape Dam.

    • Well said. Love to meet you if your interested in helping to keep river access and preserve Capes Dam.

      Look forward to hearing from you.

      Brian Olson

  8. 20 years ago, we used to swim at Sewell Park. This was back when they would dredge the river annually. The water flowed, the rice grew below, and everything was great.

    Then the rice nazis came along and the place is a fetid mess now. I saw a nutria run across the surface the other day without sinking in, the stuff is so thick and out of control.

    It’s a public health hazard and it needs to go. How long until it chokes the water flow altogether? How long until someone gets tangled in it and dies?

  9. The “deadly ricegrass” also known as Texas wild-rice is one of the reasons that our river still flows throughout the year. The other reasons are also listed as endangered or threatened species by the USFWS. These species and their habitat are protected under the Endangered Species Act, which has led to numerous measures to reduce pumping from the Edwards Aquifer, and thus ensure that the springs continue to flow year-round. Other measures have also been put in place to protect the individual species within the river. If you enjoy the river I would recommend that you do a little research on its unique species and the laws that not only protect these species but also protect the continual flow of the river. A good place to start would be the Edwards Aquifer Habitat Conservation Plan website.

  10. And yet it flowed for 1000s of years and even right up to a decade ago when all of a sudden we had to stop trimming the junk back.

    “Maintaining” the wild rice is one thing – letting it run absolutely wild across the river is another thing entirely. The complete “hands off” approach is overkill.

  11. James and L. Hilda,

    There is still a fight to keep the Dam. I truly feel this decision was rushed and one side. Who listens to one researcher before making a historical change of something that is over 160 years old?

    Also the rice is planted very often in our river and agree to that to much can not be good and soon I’m sure they will not allow any swimming in the river if a few people have it there way. That day is coming sooner than you would like to think.

    If you like to help and protect our Dam and Thompson Island please feel free to email me. I’m not interested in hate emails telling me I don’t know what I’m talking about. This is my opinion and you have yours. If you like to send me an educated opinion or fact then go ahead but keep it professional.


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