The Natural Hydrograph Concept

The science of river ecology has progressed dramatically in the last thirty-years starting with the 1972 publication of H. B. Hynes landmark book, “The Ecology of Running Waters.”1) Since release of Hynes book considerable research has occurred within individual river science disciplines as well as synthesizing this knowledge into ecological perspectives. In the 1990's numerous papers identified instream flow as the single most important factor driving fluvial distribution and life history sequences.

Applying the Natural Hydrograph Concept in Hydropower Proceedings

The scientific literature clearly demonstrates that restoration of riverine ecological processes in rivers regulated by dams requires instream flows that closely mimic the natural hydrograph present prior to dam construction2). Within the context of hydropower relicensing, restoration of the natural hydrograph has become a popular goal among state and federal agencies as well as non-governmental organizations in proceedings across the country. American Whitewater largely supports this effort in hydro proceedings where dam removal or run-of-river operations are being considered as a viable option.

In reality, most hydropower relicense proceedings do not include dam removal or run of river operations as alternatives. In these proceedings it is inappropriate to rigorously apply the natural hydrograph concept as a model for the annual hydrograph in the new license. In river reaches where hydro projects cause water to bypass significant distances of natural river channel continued power generation—the lion's share of the water in most cases– automatically eliminates the volume of water necessary to achieve the natural hydrograph and associated ecological processes. Dedicating a percentage (often times 80 to 90 percent) of the annual hydrograph to power generation makes it impossible to craft an instream flow regime mimicking the natural hydrograph. In these proceedings where hydropower consumes a significant percentage of the hydrograph strict adherence to the natural hydrograph concept is both impractical and impossible to apply across all resource disciplines. In such cases, stakeholders should view hydropower relicensing as an opportunity to develop alternative flow regimes that better balance beneficial uses than the existing or previous license instream flow conditions. Goals related to instream flows should be fashioned in a manner proportional to the alternatives being considered in the relicense proceeding. In situations where continued hydro generation and/or water diversion is part of the next license the natural hydrograph serves as a reference point but should not be a strict metric for acceptance of a flow recommendation. Alternative flow regimes should be considered with a continuum of options ranging from instream flow conditions in the existing license to that of a natural free flowing system. No single flow recommendation for a specific resource discipline should be eliminated simply because it does not comply with the natural hydrograph concept.

Items to consider when determining if the natural hydrograph is an appropriate objective/standard:

  • Does the proposed management equitably require all water uses to comply with the natural hydrograph, including the power company or dam owner. Specifically, is the proposed management either to remove the dam or to operate it as run-of-river.
  • Are there other circumstances that inherently limit ecological restoration potential such as cold-water discharges (Nantahala), water quality impacts (Ocoee), upstream flow modification (Little Tennessee), or short stream length (Cheoah).
  • Will the river be managed for native species recovery (ecological restoration) - or for non-native game fish (recreational enhancement)?

Another important consideration when considering the appropriateness of using the natural hydrograph as a standard is the restoration approach: Functional versus Structural Restoration. Often times a flow regime is proposed that “mimicks” the natural hydrograph. In this case it is not about reconstructing the exact structure of the historical flow regime, but rather aiming to restore certain functions that the historical hydrograph provided. This relies on models designed to predict specific aquatic habitat, which is a function of the flow regime. The structure of the original hydrograph is GONE due to continued power generation - so the question becomes how many ecological and social functions can we restore to a river with the left over water.

Constant variable base flows restore the following functions: Increased aquatic habitat and angling.

Variable high flow events restore the following functions: channel maintenance, sediment transport, spawning and migration cues, scouring of lentic and upland vegetation in the channel, reduction of invasive species and paddling.

How many kids can you feed with table scraps? Is it better to let some die so that others are strong or keep them all alive but weak, what happens if the kids beat the hell out of each other to be first in line, which kid deserves the food more? Playing god with instream flows is really about social values engineering. The end result in most relicense proceedings is power generation alterations to the hydrograph are acceptable because they are expected socially as a traditional use, base flows meeting traditional angling needs are acceptable because predictive models say they are, but whitewater flows are perceived as unknown ecological risks or “disturbances” and thus required to strictly follow the structure of the Natural hydrograph. This is a mistake because as previously stated - the natural hydrograph no longer exists.

The point being that low flows are restored to functionally mimic the natural hydrograph, while high flow events are often forced to structurally comply with the natural hydrograph, when in reality both are functional restoration. If both can be considered as critical to restoring a wide array of valuable social and ecological functions then realistic functional river restoration can be achieved.

In relicense proceedings where decommissioning is not an alternative state and federal agency resource managers and non-governmental organizations must clearly define their resource management goals and objectives. Complete restoration of natural conditions is not feasible given the lack of project decommissioning. Stakeholders must scale back their river restoration goals proportional to the volume of water remaining for instream flows. Stakeholders should focus on developing alternative flow regimes designed to meet individual resource goals and objectives. The alternative flow regimes should be designed in a fashion that strives to enhance aquatic resources/riverine ecological processes without causing impact. No single beneficial use should dominate the alternative flow regime developed as the annual hydrograph for the new power license. Resource managers should resist developing an alternative flow regime that focuses on a single species or species guild particularly when that alternative restricts and/or eliminates other beneficial uses. Instream flows should be dynamic in time and volume to stimulate habitat and species diversity3). Evaluations of alternative flow regimes should be based on objective scientific study meeting peer review standards.

Most instream flow recommendations on regulated rivers revolve around fishery needs. Typically, fishery instream flow recommendations are less than 10 percent the volume of the natural hydrograph and have little if any seasonal variation. This is referred to as a flat-line hydrograph because of the lack of peaks and valleys predominant in a natural hydrograph. Riverine ecological processes are driven by the peaks and valleys in the annual hydrograph. The aquatic habitat and associated biological community are manifested by the hydrologic peaks and valleys. It is not uncommon for resource managers to prescribe a flat-line instream flow for the fishery and in the same meeting object to pre-project whitewater releases under the pretense that the rate of change between the artificial base-flow and the whitewater release is not natural. This selective application of the Natural Hydrograph Concept is simply a self-serving argument against whitewater flows with no scientific merit. Ironically, it is the proposed whitewater flows that more closely mimic the natural flow than the proposed fishery instream flow. Admittedly, the flow fluctuations were not present in the pre-project hydrograph. But since the stakeholder group is not truly reconstructing the natural hydrograph then why is the whitewater constituency required to uphold the natural hydrograph paradigm while the fishery flows blatantly violate the concept? All beneficial uses should adhere to the same standards be it hydropower generation, fisheries/aquatic organisms or angling? The inconsistent application of the natural hydrograph concept is a symptom of stakeholders not clarifying resource goals and objectives in a proceeding and applying those goals and objectives uniformly.

Any proposed whitewater schedule should be evaluated through empirical scientific study rather than paradigms about natural hydrographs applied inconsistently across resource disciplines. Resource managers should be developing testable hypothesis related to their biological concerns about whitewater releases. Do the whitewater fluctuations cause a biological impact? What is the difference biologically between whitewater fluctuations, project shut-downs and spill flows? Is the recorded biological impact long term or short term i.e., does it cause a decrease in the inter or intra-annual population? Are these biological impacts the result of a synergistic interaction between degraded habitat and fluctuating flows? If the habitat improved would the flow fluctuations have a biological impact? These questions need to be asked and carefully tested. Assumptions should be carefully tested.

Clean Water Act Compliance

The California Water Quality Control Board, the state agency responsible for administering the federal Clean Water Act, recognizes 21 beneficial uses on the Pit River. The Basin Plan states the following:

“Beneficial uses are critical to water quality management in California.

State law defines beneficial uses of California's waters that may be

protected against quality degradation to include (and not be limited to)

”…domestic; municipal; agricultural and industrial supply; power

generation; recreation; aesthetic enjoyment; navigation; and preservation

and enhancement of fish, wildlife, and other aquatic resources or preserves”

(Water Code Section 13050(f)). Protection and enhancement of existing

and potential beneficial uses are primary goals of water quality planning.”4)

The US Forest Service has an obligation under a Memorandum of Understanding with the California Water Quality Control Board to uphold federal Clean Water Act water quality standards and regulations for the respective reaches of the Pit River in this relicense proceeding. The Basin Plan for the Sacramento Basin specifically designates canoeing and rafting as Recreation I beneficial uses for the Pit 3, 4 and 5 reaches. As such, these beneficial uses are protected by state and federal regulations. The US Forest Service cannot issue draft 4(e) conditions that categorically deny a beneficial use particularly when the rational for precluding a beneficial use is based solely on assumptions rather than conclusive evidence. Proposed 4(e) conditions that exclude or eliminate a beneficial use would violate the Antidegradation regulations. The Antidegradation policy can be found at http://www.swrcb.ca.gov/plnspols/wqplans/res68-16.html. The US Forest Service must balance existing beneficial uses with resource protection objectives. Those objectives must be based on objective scientific data and be proportional to the specific percentage of natural the US Forest Service is attempting to restore. If the US Forest Service goal is to restore one-hundred percent natural in the Pit River, then the project facilities must be removed. If the goal is less than one-hundred percent of natural, then all objectives in specific disciplines should be scaled back accordingly.

The FERC is also from a regulatory standpoint responsible for upholding the Clean Water Act water quality standards and regulations identified in state water quality standards. California's Sacramento River Basin Plan can be found at http://www.swrcb.ca.gov/rwqcb5/available_documents/index.html#anchor616381

1) Hynes, H. B. 1970. The Ecology of Running Waters. University of Toronto Press, Toronto. 555 p.
2) Stanford, J.A. et. al.. 1996. A general protocol for restoration of regulated rivers. Regulated River: Research and Management 12:391-413. Richter, B.D., J.V. Baumgarten, J. Powell, and D.P. Braun. 1996. A method for assessing hydrologic alteration within ecosystems. Conservation Biology 10(4):1163-1174. Richter, B.D., J.V. Baumgartner, R. Wigington, and D.P. Braun. 1997. How much water does a river need? Freshwater Biology 37:231-249. Poff, N.L., J.D. Allan, M.B. Bain, J.R. Karr, K.L. Prestegaard, B.D. Richter, R.E. Sparks, and J.C. Stromberg. 1997. The natural flow regime: a paradigm for river conservation and restoration. Bioscience 47(11):
3) Resch et al. 1988. River Continuum Concept.
4) The Water Quality Control Plan (Basin Plan) For The California Regional Water Quality Control Board Central Valley Region, Fourth Edition – 1998. The Sacramento River Basin And The San Joaquin River Basin
Join AW and support river stewardship nationwide!