Connecting Flows and Water Quality: Middle Cuyahoga TMDL

Habitat and flow impairments are often thought of as untouchables in the Total Maximum Daily Load (TMDL) world. Common thinking about the program has been strictly focused on calculating a limit for a specific pollutant, which is then apportioned as an overall load among point and nonpoint sources of pollution.

Although load reduction is the heart of the TMDL approach, it doesn’t have to be that narrow. For example, the Ohio Environmental Protection Agency (OEPA) has long viewed the TMDL program just a little differently than other states. In part, this is a result of Ohio’s extensive biological monitoring program and the existence of strong biological metrics in its water quality standards which allow the state to focus on attaining designated uses rather than only on a chemical surrogate.

As a result, Ohio TMDLs consider both reducing loads and building assimilative capacity– coming at pollution problems from both sides of the equation. While load reductions might include activities like tightening permit limits and establishing best management practices, increasing a stream’s assimilative capacity might also include increasing the shade canopy over a stream or improving in-stream flows. Using both approaches has allowed the state to create TMDLs that both achieve a specific water quality criterion and improve overall stream function.

The state creates TMDLs which link a specific measure – for example, the state’s biocriteria standard – with a response indicator such as dissolved oxygen. That response indicator is then tied to an exposure indicator like nutrients or carbonaceous biochemical oxygen demand. Lastly, that exposure indicator is tied to stressors, such as wastewater discharges, habitat modification and flow. So in this example the TMDL might recommend load reductions by changing wastewater treatment plant’s permitted discharges for nutrients and oxygen demanding substances and boosting assimilative capacity by restoring the stream channel so it is better able to naturally process the remaining nutrients.

The Middle Cuyahoga TMDL serves as a good example of Ohio’s approach. Since the ‘70s, the Cuyahoga has seen large improvements in chemical and physical water quality. However problems remain, particularly in the biology of the system. For example, the middle Cuyahoga was declared impaired by habitat and flow alteration, excessive nutrient levels and low dissolved oxygen. The OEPA identified flow modification, impoundments and municipal discharges as the sources of these problems.

The overall goal of the TMDL was to achieve Ohio’s biological water quality criteria. The TMDL established a target for dissolved oxygen as a proxy for progress toward meeting the biocriteria. To achieve the dissolved oxygen target, the TMDL identified the need to control nutrients and carbonaceous biochemical oxygen demand (CBOD), as well as address impoundments and flow modification problems.

How did the TMDL tie in the impoundments and flow issues? Lake Rockwell, a drinking supply reservoir located on the Cuyahoga mainstem, deprived Middle Cuyahoga of flows. This resulted in very low dissolved oxygen readings below the dam – at times as low as 0.0 mg/L. Two smaller dams located in the Middle Cuyahoga downstream from Lake Rockwell exacerbated the problem and greatly diminished the assimilative capacity of the river, resulting in the need for tighter effluent limits for the wastewater treatment plants discharging to the reach. The physical presence of the dams themselves also harmed designated uses directly by limiting fish passage.

In the TMDL the OEPA laid out two possible implementation scenarios. The first scenario envisioned a voluntary mix of activities that included a minimum release of 3.5 MGD from Lake Rockwell, along with removal or modification of the Munroe Falls and Kent Dams.

However, if the actions identified in the first scenario were not completed within a specified timeframe, the second, regulatory scenario would come into play. In this scenario, much stricter (in some cases zero) pollutant load limitations for CBOD and ammonia would be placed on all six of the wastewater treatment plants in the TMDL study area.

The City of Kent’s website describes the decision confronting local governments: “The City was also informed that refusal to pursue and initiate a modification-removal of the dam would result in more stringent permit limits at the City’s Water Reclamation Facility (WRF). City officials knew that additional infrastructure at the WRF would be an expensive venture for Kent taxpayers and would yield minimal benefits to the river water quality.”

As a result, the first scenario won the day. A minimum flow release from Lake Rockwell was agreed upon. The historic Kent dam was modified in 2004 and the Munroe Falls dam was removed altogether in 2005.

Within a year of removing Munroe Falls dam, OEPA data showed dramatic improvements in the fish community and improvements in dissolved oxygen levels. By December 2009, dissolved oxygen criteria were met in the river, and the condition of the warmwater aquatic life community had improved dramatically, meeting state criteria for the diversity of the macroinvertebrate community and physical habitat. One stretch still does not meet the criteria for healthy fish communities, but it is on the way to full recovery.

By using all the components of the system (physical, biological and chemical) to inform the TMDL process, rather than take a myopic pollutant-specific approach, OEPA was able to offer the two scenarios as a way to meet the challenge. In the end, this type of creative thinking resulted in benefits far beyond simply load reductions for the river, the fish, and the communities along the mighty Middle Cuyahoga.

The take home lesson here is that a flow or habitat problem may be more easily incorporated into the TMDL structure when it is related to a more traditional pollutant. Temperature, dissolved oxygen, nutrients, and many other more traditional parameters can be tied back to flow and habitat concerns. Even if a state is resistant to the idea of a flow or habitat TMDL, it may be possible to make the case that addressing flow or habitat alterations instead of (or along with) the traditional pollutant will save time and money, while providing a wider range of benefits.

Of course the real measure of success is neither the reduction of a targeted pollutant nor the achievement of a particular flow regime…rather success will be measured by the return to health of the ecosystem. This is where this example benefits from Ohio’s robust biocritiera program, which will ultimately document success through the recovery of the biological integrity of the system.

Explore more ideas for connecting Clean Water Act policies with flow restoration and protection.