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FLOW MANAGEMENT: Studying Ramping Rate Restrictions

Two natural resource agencies, a university, and a power producer are working to test whether regulation of ramping rates of hydroelectric turbines can provide ecological benefits while, at the same time, minimize production losses. Results could lead to the design of better tools for optimal management of various water uses.

By Karen E. Smokorowski, Robert A. Metcalfe, Nicholas E. Jones, Jérôme Marty, Shilei Niu, and Richard S. Pyrce

Fisheries and Oceans Canada, the Ontario Ministry of Natural Resources, Brookfield Renewable Power Inc., and the University of Waterloo are collaborating on an adaptive management experiment on the Magpie River in Ontario, Canada. Brookfield Renewable Power owns a hydro facility on the river, Fisheries and Oceans Canada is acting as the lead science coordinating agency, the Ontario Ministry of Natural Resources is the agency in charge of regulating water at hydro facilities in Ontario, and the University of Waterloo is providing experts in stable isotope food web analysis and economic analysis.

The goal of this experiment, which began in 2002, is to test whether restricting ramping rates (the rate of change of water flow) through turbines at hydroelectric facilities can provide ecological benefits while, at the same time, minimize production losses.

For the purposes of this article, “ramping rate” refers to the rate of change of water flow (in cubic meters per second per hour) and “peaking” refers to the mode of operation of a facility where water is released in accordance with electricity demand. Unrestricted ramping allows operators to adjust flows rapidly to meet peak demands; restricted ramping requires operators to adjust flow more slowly, reducing the ability to meet peak demands and/or passing water through turbines in excess of that dictated by market forces.

Water is an important resource for Ontario; hydroelectric facilities provide 24.5 percent of the province’s installed electrical generating capacity.1 In addition, hydro projects are the province’s largest source of natural resource-based revenue, at C$1.7 billion (US$1.4 billion) annually.

Provincial law requires owners of water power facilities in Ontario to develop Dam Operating Plans. These plans set operational requirements for management of water flows and levels (e.g., minimum flow requirements and ramping rate restrictions) that are enforceable by law. Resource managers believe that ramping rate restrictions mitigate the negative effects associated with dam operation, including habitat degradation and reduction of downstream diversity.2 In reality, there is a paucity of information on the ecological benefits or possible damage of these restrictions. It is clear to operators of hydro facilities that ramping rate restrictions impede the efficiency and profitability of hydro operations.

It is important to assess the downstream effects of ramping rate restrictions in comparison with unlimited ramping and to develop the scientific information necessary to design management tools that address both ecosystem integrity and energy efficiency. The main purpose of the adaptive management experiment on the Magpie River is to determine if removing all operational constraints on ramping rates is detrimental to the downstream riverine ecology. A secondary purpose is to examine the effect of ramping restrictions on the economics of two hydro facilities on the Magpie River in Ontario: 15.5-MW Steephill Falls and 12.5-MW Harris.

Researchers are using a BACI (before-after-control-impact) design for this ecosystem-level experiment. This design involves comparing conditions on a regulated (impact) river to conditions on a reference (control) river before and after implementing a change in ramping rates. This approach should allow detection of a change in physical (hydrology and geomorphology) and biological (invertebrates, fish, and food web) measures that were caused by the experimental ramping rate changes.

The experimental site is the 40-kilometer stretch of the Magpie River between Brookfield Renewable Power’s Steephill Falls and Harris facilities, both of which began operating in the early 1990s. The reference river is the unregulated Batchawana River, about 60 kilometers north of Sault Ste. Marie, Ontario. From 2002 to 2004, researchers collected data under the original restricted ramping rate regime: ramping rate could not exceed 1 cubic meter per second (cms) per hour October 10 to November 15 and 2 cms per hour November 16 to spring freshet (early May); from May to October 9, flow could only increase or decrease by 25 percent of the previous hour’s flow. From 2005 to 2007, researchers collected data with no restrictions on ramping and while the Steephill Falls plant operated in accordance with water availability and market forces. During the entire study period, the Steephill Falls facility had a minimum discharge of 7.5 cms.

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Initial results, reached in 2007, indicate a typical dampened hydrograph in the Magpie River relative to an unregulated river. In the Magpie, unlimited ramping resulted in a greater time at the minimum and maximum turbine flows and less time at intermediate flows compared to the restricted ramping period. The physical characteristics of the river bed were affected by flow regulation in terms of localized channel widening, channel incision, and alteration of natural bedload movements. Only tolerant invertebrates are abundant in the wet-dry zone of the Magpie River, and the transition to unlimited ramping reduced invertebrate diversity in the permanently wetted zone, caused by a reduction of environmentally sensitive taxonomic categories. Unlimited ramping did affect individual fish for sensitive species. However, the fish communities (i.e. species composition and community biomass) were not significantly affected by ramping. Food web analysis suggests that unlimited ramping resulted in a significant change in fish diets and a reduction in food web complexity.

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Measuring physical changes

The two physical changes researchers are measuring during this experiment are hydrology and geomorphology. The sections below give details on these two parameters.

Studying flow patterns in the Magpie River
Historical flow records illustrate the natural flow pattern and variability in the Magpie River before regulation (see top image, Figure 1). Batchawana River’s streamflow pattern strongly resembles the natural pattern of the Magpie River before regulation (see bottom image, Figure 1), indicating it is an appropriate control site for monitoring natural variability.

The streamflow pattern at Steephill Falls reflects variable energy demand and water supply within technological and regulatory constraints. These constraints include a maximum flow of 45 cms through the turbines and requirements for minimum ecological flow of 7.5 cms. The flow pattern with ramping restrictions and unlimited water supply typically would involve minimum flows on weekends and a saw-toothed pattern on weekdays, perched on an elevated base flow (see left side of top image, Figure 2). The flow pattern dampens when water supply is less (see right side of top image, Figure 2) and is curtailed severely under even drier conditions (see center of top image, Figure 2). During unlimited ramping, the minimum flow requirement and maximum flow through the turbines were attainable on a daily cycle, and less volume of water was required for a peaking event. This allowed short-duration peaking even during drier conditions (see right side of bottom image, Figure 2).

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Flow alteration at Steephill Falls typifies peaking facilities in that the range of flows is dampened (see bottom of Figure 3) compared to natural flow regimes (see top of Figure 3). Other variables affecting the shape of the flow duration curve on the Magpie River are the maximum turbine flow and minimum flow constraints (see bottom of Figure 3).The percent of time at these two flow magnitudes largely depends on water availability and ramping rate restrictions. The flow duration curves reflect the transition to unlimited ramping, with greater time at the minimum flow, less time at intermediate flows, and greater time closer to the maximum turbine flow (see bottom of Figure 3).

Fluvial morphology and coarse sediment transport
Researchers surveyed 41 cross-sections on the Magpie River and 38 on the Batchawana River to characterize and classify channel morphology.3 Physical measurements also included bank full width and depth, flood prone width, channel sinuosity, surface water slope, and river bed material sediment size. The Magpie River is dominated by meandering, gravel-bed, riffle/pool sections with well-developed flood plains. In contrast, the Batchawana River cross-sections are a mix of channel types, with an emphasis on deeply incised and entrenched gravel-bed, meandering-type sections of river. Channel morphology is controlled by natural evolution of the rivers; however, the Magpie River is modified by the regulated flow regime.

Researchers used discharge data combined with longitudinal slope and sediment size information to solve a simple excess shear stress equation4 for flow depth, to determine at what flow bed sediment movement (i.e., channel change) occurs. Researchers investigated select cross-sections of the Magpie River to consider bed load transport under regulated discharges downstream of the Steephill Falls plant. For one site 13.5 kilometers below Steephill Falls, the discharge required to initiate bed sediment transport is 80.4 cms. Regulated flows for 2005 and 2006 fluctuated almost exclusively between 7.5 cms and 45 cms. Thus, it is likely that no bed load transport occurred at this site during this time period. Casual snorkelling of the river showed bed load movement at discharges lower than 45 cms at other sites in the river,5 indicating lower discharges can transport bed load at locations with smaller bed sediment and steeper bed slope. The bed load transport study will be followed up by field work in 2009 and 2010 to confirm discharge thresholds for movement of bed sediment.

In the lower part of the Magpie River study reach, there is evidence of channel bank incision. Continual regulated flow stage fluctuations have caused this erosion and subsequent occasional bank collapse, producing localized channel widening. This is certainly a direct response to the regulated flow regime produced by the Steephill Falls plant.

Measuring biological changes

During this experiment, researchers measured three biological changes: benthic invertebrates, fish, and food webs. The sections below give details on these three parameters.

Benthic invertebrates
There is little published research on the composition and abundance of benthic invertebrates within regulated rivers where the stream bed is wetted and dried repeatedly at a high frequency. The large daily flow change on the Magpie River, which translates to a 10 to 50 percent change in wetted width, raises the question: How productive is the portion of stream bed that repeatedly becomes wet and dry, relative to the permanently wetted zone?

For this study, researchers examined patterns in benthic community characteristics along transects perpendicular to the flow, where strong environmental gradients develop because of flow regulation. In addition, researchers performed a detailed study of invertebrates using rock bags in the permanently wetted zone. (Rock bags are coarse mesh bags filled with cleaned rock from the surrounding substrate and left to colonize for a period of time.) This research was intended to test the hypothesis that constant wetting and drying would result in low benthic invertebrate biomass in the wet-dry zone, with only the most tolerant invertebrates succeeding in such a harsh environment. In contrast, researchers hypothesized that invertebrates in the permanently wetted zone may experience more favorable environmental conditions under restricted ramping due to maintenance of a minimum flow and would respond negatively to unlimited ramping due to increases in shear stress, potentially causing catastrophic drift.

Differences in the distribution and abundance of invertebrates depended on distance from the dam and the shore. Transects less than 8 kilometers from the dam had much higher (30 times in some cases) densities of stream- and lake-derived invertebrates. Areas close to shore in the Magpie River contained invertebrates capable of withstanding harsh environmental conditions, such as snails and oligochaetes. More environmentally sensitive invertebrates (such as mayfly and caddisfly) were scarce in near-shore areas but up to 14 times more common in deeper offshore samples of the river. In contrast, the density of benthic invertebrates in an unregulated reference river typically is highest (one to 20 times) near the shore. Results from the rock bags showed that overall invertebrate abundance was significantly higher in the Magpie River across all years. However, after unlimited ramping, invertebrate diversity decreased significantly, with a corresponding decrease in the proportion of environmentally sensitive invertebrates.

Poor production of benthic invertebrates or production of invertebrates undesirable as forage (such as snails and very small burrowing worms) could have important implications for small and young-of-the-year fish. Most small fish spend much of their time in the shallow water along the river edge, to avoid higher flows and predators. A lack of profitable feeding areas in shallow water could force small fish to move into deeper water, where they would face increased predation risk and higher metabolic demands. Ultimately, the habitat switch might lead to fewer and smaller forage and juvenile fish.

Fish
Fish and their habitats are affected by flow changes, but responses can vary and there is a need for more rigorous study designs.6 Many of the studies within this experiment were undertaken to determine both the cause and the mechanisms behind any changes in the fish community. Consequently, studying changes in fish community structure and biomass was one of the main components of the monitoring program. By collecting data on fish abundance, biomass, diversity, growth, condition, and population age structure, we can test hypotheses. For example, one hypothesis might be that unlimited ramping reduces fish diversity, shifts dominance to more tolerant species, and decreases growth and the condition of sensitive species but would not affect total fish community biomass.

Fish biomass was two to three times more variable within and among years on the Magpie River at sites closer to the dam than at sites further from the dam or on the Batchawana River. Total fish community biomass was similar both before and after unlimited ramping on the Magpie River. There is some indication of reduced biomass in the fast-flowing habitat of the river relative to the Batchawana River. Fish diversity was unchanged on average on both rivers before and after unlimited ramping, but in both periods fish diversity was significantly greater on the Batchawana River (greater than 10 percent). Fish condition (weight for a given length) was not affected for more tolerant species (such as longnose dace or sculpin), but a significant effect was detected in more sensitive species (such as brook trout and trout perch). Individuals weighed significantly less after ramping changes on the Magpie River. Thus, while there is a significant indication of an effect of unlimited ramping rates at the level of individual fish for sensitive species (i.e., weight of fish at a given length), the fish communities (i.e., species composition and community biomass) appear not to be significantly affected by ramping.

Food webs
Changing flow patterns may alter how organisms interact. The food web defines feeding relationships by documenting predator/prey relationships and how energy enters the food chain.7 Flow changes can affect the competitive abilities of organisms, altering relative abundance, including favored prey items. Changes in prey availability can cause organisms to alter diets, which leads to increasing competition and/or changing total energy intake. These changes can cause alterations in growth that, in turn, can change reproductive rates and influence species’ population dynamics.

Changes in the food web often are quite subtle, and detecting them requires building a detailed picture of the feeding relationships among organisms. Based on stable isotope analysis, ecologists have characterized energy sources of organisms using carbon isotope composition, as well as the relative position of species in the food web using nitrogen isotope composition. Because few studies have attempted to investigate what might happen to food webs when the regulation regime on a river changes, as part of this study researchers undertook a study of the food webs. Specifically, the study set out to test the hypothesis that peaking without ramping restrictions would alter the food web by changing the mix of terrestrial and algal carbon sources and by reducing the length of the food web. In unproductive systems, algal carbon is the most limiting but also most important food source compared to terrestrial inputs.

Studies to date have shown little effect of ramping on the energy sources (carbon) entering river food webs, with most differences observed between regulated and unregulated rivers. In regulated systems, carbon cycling is influenced by processes (respiration, photo-oxidation, and anoxia) occurring in upstream reservoirs and likely is responsible for lower carbon signatures (a 3 per mil difference on average, equivalent to an 8 percent decrease). Changes in the nitrogen values seen in invertebrate and fish species, however, suggest a reduction in food chain length under unrestricted ramping rates. Specifically, fish nitrogen signatures were lower under unlimited ramping rate conditions. Because such a trend was not observed for their prey (invertebrates), this result indicates a significant change in fish diets and a reduction in food web complexity.8 Reductions in complexity concern ecologists because they could make systems more vulnerable to subsequent stressors.

Determining the economics of ramping rates

A study concurrent to the ecological studies described above examined the economics of ramping rate restrictions. The goal was to determine how these restrictions may affect peak production of a hydro facility, with a view to understanding how biological-based regulation might constrain the economics of plant operations. Ideally, ramping rate regulations would promote a healthy environment for fish while allowing hydro facilities to satisfy peak power demands. With no restrictions, operators can maximize economic benefits by adjusting the magnitude, timing, duration, and rate of change of flow below the facility – ramping up when prices/demand are high and down when prices/demand are low. There are few studies that examine power supply effects and the costs of ramping restrictions9,10 and none that attempt to integrate economic modeling directly with science-based studies.

Researchers analyzed the cost of ramping rate restrictions using a generic model for a mid-sized peaking plant (from 10 MW to several hundred megawatts). This economic profit maximization model, which was subject to various levels of ramping rate restrictions, was based on data provided by an industry partner. The model maximizes the value of a representative hydro facility subject to various physical and environmental constraints, plus a requirement to meet a specified level of electricity demand. Experiments with the model demonstrated the sensitivity of the economic benefits to various levels of ramping restrictions, as well as how specific operational parameters of the facility affect that sensitivity. Preliminary results demonstrate a potential insensitivity of economic benefits to ramping rates over a limited range. In conjunction with the results of the ecological study, the conclusions of the economics study will be helpful in the design of ramping rate regulations that take account of both the biology and economics of a river-dam system. These results will be available in 2009.

Researchers incorporated consideration of the use of alternative generating capacity in the model. For example, widespread ramping restrictions could force the power grid to rely more heavily on other, more costly peaking facilities with increased emissions of greenhouse gases. To inform the model, researchers assumed that any ramping restrictions would result in increased use of fossil fuels and included an environmental cost in terms of dollars per ton of extra carbon emitted.

Future research planned

This research project constitutes a significant undertaking. Many challenges were encountered, including sampling methodology difficulties specific to working on peaking systems. Subsequent refinement resulted in an important methodological contribution to future research and monitoring on peaking hydro facilities, in the form of standardized sampling protocols.

Coincident with the change to unlimited ramping undertaken to perform this study was the onset of a drought resulting in three dry years with above average temperatures and lower-than-normal flows on all rivers, including the reference river. This resulted in increased capacity in the reservoirs on the Magpie River to store a complete spring freshet, which reduced the magnitude and frequency of ramping relative to a normal water-level year. A spring freshet, although reduced, still occurred on the reference river. Therefore, all results need to be viewed with caution regarding the causative factor: Are effects the result of changes in ramping or drying conditions? Funding opportunities are being explored to extend the study and clarify the effects of climate vs. ramping.

Results of this and ongoing studies will help inform Canadian provincial and federal waterpower guidelines and policy, facilitating science-based decisions regarding ramping at hydro facilities. In addition, methodologies developed will be used to help establish effectiveness monitoring programs for Dam Operating Plans at existing and new hydro facilities in Ontario.

The economic model created in this study captures the key relationships between the value of power and ramping rates, which provides important intuition for balancing environmental and economic concerns. Results from this research should facilitate the implementation of environmental regulations designed to promote the integrity of river systems, as well as to provide a set of planning tools regulators and industry can use to negotiate the optimal ramping rate for environmental and economic benefits.

Notes

  1. www.ieso.ca/imoweb/media/md_ supply.asp.
  2. Sabater, S., “Alterations of the Global Water Cycle and Their Effects on River Structure, Function and Services,” Freshwater Reviews, Volume 1, No. 1, March 2008, pages 75-88.
  3. Rosgen, D.L., Applied River Morphology, Wildland Hydrology, Pagosa Springs, Colo., 1996.
  4. Dubinski, I.M., and E.E. Wohl, “Assessment of Coarse Sediment Mobility in the Black Canyon of the Gunnison River, Colorado,” Environmental Management, Volume 40, No. 1, July 2007, pages 147-160.
  5. Smokorowski, K., personal communication, 2008.
  6. Murchie, K.J., et al, “Fish Response to Modified Flow Regimes in Regulated Rivers: Research Methods, Effects and Opportunities,” River Research and Applications, Volume 24, No. 2, February 2008, pages 197-217.
  7. Peterson, B.J., and B. Fry, “ Stable Isotopes in Ecosystem Studies,” Annual Review Ecology and Systematics, Volume 18, 1987, pages 293-320.
  8. Marty, Jérôme, Karen E. Smokorowski, and M. Power, “The Influence of Fluctuating Ramping Rates on the Food Web of Boreal Rivers,” River Research and Applications (in press).
  9. Edwards, B.K., S.J. Flaim, and R.E. Howitt, “Optimal Provision of Hydroelectric Power under Environmental and Regulatory Constraints,” Land Economics, Volume 75, No. 2, May 1999, pages 267-283.
  10. Thompson, M.I., M. Davison, and H. Rasmussen, “Valuation and Optimal Operation of Electric Power Plants in Competitive Markets,” Operations Research, Volume 52, No. 4, July-August 2004, pages 546-562.

Acknowledgments

For their intellectual contributions to the project, as well as their written contributions to this article, the authors thank Drs. Michael Power and Margaret Insley, University of Waterloo; Scott Finucan, Ontario Ministry of Natural Resources; and Rob Steele, Natural Resource Solutions Inc. representing Brookfield Renewable Power Inc. The authors also thank the biologists, technicians, students, and others who assisted with the field and lab work, particularly Lisa Voigt, William Gardner, Marla Thibodeau, Nathan Hanes, Chelene Krezek, and Ainsley Latour. In addition to extensive support by project partners, financial support was provided by Ontario Centers of Excellence, Canadian Foundation for Innovation and Ontario Innovation Trust, and Ontario Power Generation.


Karen Smokorowski, PhD, is a research scientist at the Great Lakes Laboratory for Fisheries and Aquatic Sciences, Fisheries and Oceans Canada. Robert Metcalfe, PhD, is science coordinator with the Renewable Energy Section of the Ontario Ministry of Natural Resources (MNR). Nicholas Jones, PhD, is a research scientist with the River and Stream Ecology Lab of the Ontario MNR. Jérôme Marty, PhD, is a research scientist with the St. Lawrence River Institute. Shilei Niu is a PhD candidate with the economics department at the University of Waterloo, studying the economics of ramping rate restrictions. Richard Pyrce, PhD, is a regional hydrologist with the Northeast Science & Information Section of the Ontario MNR.

This article has been evaluated and edited in accordance with reviews conducted by two or more professionals who have relevant expertise. These peer reviewers judge manuscripts for technical accuracy, usefulness, and overall importance within the hydroelectric industry.


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