From Water Wiki
Instream flow is the amount of water needed in a stream to adequately provide for downstream uses occurring within the stream channel. These users cover some or all of the following uses that extend beyond the need for human drinking water: aquatic habitat, recreation, wetlands, navigation, hydropower, riparian vegetation, and water quality, including waste assimilation. Flow is measured in volume of water per unit of time, usually cubic feet per second (cfs). This gauges the amount of water flowing past a point in the river at a given time.
Reduced stream flow can interfere with any or all of these uses and destroy aquatic and floodplain habitat. Reduced flows also cause loss of certain fish and wildlife species, increased erosion and sedimentation, and increased concentration of pollution (including stormwater runoff), as well as the loss of river recreation opportunities. On the other hand, excess flows can also wreak havoc on instream uses and the riparian habitat that is critical for many aquatic species. For example, The Nature Conservancy has found that continual releases of 20,000 cfs from the Kerr Lake/Lake Gaston/Roanoke Rapids reservoir system into the lower Roanoke River floods the bottomlands hardwood riparian systemstriped bass and American shad ecological flows."
FAQ from the Instream Flow Council:
What is instream flow?
At its most basic level, the term means water flowing in a stream. Most streams have some level of flow, but flow is no guarantee that all is well for the organisms (including humans) that depend on the river’s resources. Natural resource managers are faced with the complicated task of protecting and restoring public values to rivers while honoring existing uses.
Why is instream flow important?
Natural stream and river systems provide many beneficial values and services, including flood mitigation, groundwater recharge, navigation, nutrient transport and recycling, pollution attenuation, water supplies, biological productivity, aesthetic values, and recreational opportunities such as fishing, boating, swimming, and wildlife viewing. Instream flow is necessary to sustain these and other utilitarian and intrinsic values. A good understanding of how instream flow levels and regimes relate to these values, and the scale of alteration from the natural condition, is necessary for informed river management.
How does one determine how much flow a river needs?
There is usually not just one flow level that a river needs to stay healthy. If the objective is to preserve riverine values, that can only be done by preserving the processes and functions of the river ecosystem. The structure and function of riverine systems are based on five riverine components; hydrology, geomorphology, biology, water quality, and connectivity. Inter- and intra-annual flow prescriptions are needed to preserve the ecological health of a river. And some flow needs, such as those that flush sediments from stream substrates or maintain channel integrity, may be quite high.
Isn't instream flow really an issue of “water for fish” vs. “water for people”? Aren't people more important than fish?
Ways to assess and represent instream flow requirements
Flow requirements are often thought of as minimum flows or releases, but they can also include maximum flow limits for peaking hydropower dams, seasonal releases for fish spawning, or weekend releases for recreation. There are a variety of statistics and methods used to set flow requirements.
Instream uses of water depend on the stream, the intended use, and vary by season. Flows that provide adult fish habitat may be different than those needed for reproduction during the spawning season.
Much of the following discussion comes from the Georgia Water Coalition's FAQ on instream flows:
7Q10 is the lowest flow expected to occur on a particular stream for 7 consecutive days once every 10 years.
'Monthly 7Q10is the lowest seven-day running average of a stream’s flow for each calendar month with a recurrence frequency of once in ten years. In a water supply reservoir, the applicant must release the lesser of the monthly 7Q10 or the inflow to the reservoir. For an instream withdrawal, the applicant is at all times required to pass the lesser of the monthly 7Q10 or the inflow at the withdrawal point. The monthly 7Q10 value is essentially a drought-level value, and flatlining a stream’s flow at such a value can have negative impacts on water quality for the reasons given above. '''''
Mean (average) annual flow option or a percentage of mean annual flow:
30% Mean Annual Average Flow: For direct water withdrawals out of a stream, the applicant must allow the lesser of 30% of the mean annual flow of the stream or the inflow (the amount of water coming to the intake point) to pass the instream withdrawal point. 30/60/40% Mean Annual Flow: For reservoir applications, the applicant is at all times required to release from the reservoir, the lesser of 30% of the mean annual flow or inflow during the months of July through November; 60% of the mean annual flow or inflow during the months of January through April; and 40% of the mean annual flow or inflow during the months of May, June, and December.
What is the most important factor when determining instream flow?
Natural flow variability is one of the most important components of any healthy stream and instream flow policy. It is not only the amount of water in a stream, but the variability of that quantity throughout the seasons, months and even days that supports species habitat. In addition, the presence of adequate high and low flow pulses are important indicators of the health of an aquatic community. Flatlining is removing the flow variation in a river, and reducing it to a low, constant flow – essentially a permanent drought flow. By removing this variability in stream flow, aquatic habitat is destroyed and water quality is degraded, making flatlining one of the greatest threats to many species in our rivers and streams.
What is the ideal method of determining instream flow?
Ideally, all instream flows would be determined by focused, scientific, sub-basin studies to evaluate aquatic habitat and water demands specific to each region. A satisfactory flow regime would include planning by region and on a basin level, as opposed to a statewide policy which embodies a one-size-fits-all mold creating mandatory minimum flows, which may lead to flatlining.A site-specific instream flow study is a study that an applicant may perform to determine what minimum flow conditions must be maintained for protection of aquatic habitat. Like all ideals, however, this one is constrained by resource requirements: how much time and funding is available to do the site-specific studies.
Q. How do dams affect rivers and streams?
Since dams interrupt the natural flow of rivers and often release water based on hydropower generation peak hours rather than ecological requirements, adequate minimum flow standards are crucial just below dams. However, a single minimum flow value can lead to flatlining. Many dams are designed to release only certain minimal amounts of water; even the ones designed to vary the quantities of water released do not always coordinate the releases with the natural seasonal variability that rivers need to maintain their natural biota.
Instream Flow consists of five riverine components:
1. Hydrology: properties, distribution, and effects of water on the earth’s surface, in the soil and underlying rocks, and in the atmosphere. (from www.answers.com).
a. land use practices such as draining wetlands, channelization, and water withdrawals all alter flow regimes.
2. Geomorphology: shape of the stream channel
a. physical habitat is essential to maintain aquatic communities formed by periods of disturbance.
3. Biology: composition of the biological community.
4. Water Quality: the physical, chemical, and biological attributes of water.
a. the amount of flow affects the maintenance of water quality.
5. Connectivity: the flow, exchange, and pathways that move energy, organisms, and matter through systems.
Other components of Instream Flow include public involvement and the legal and institutional frameworks:
1. Public Involvement: the public has a legitimate right and responsibility to be involved in the decision making process.
a. public involvement will increase support for Instream Flow protection.
2. Legal/Institutional: the Public Trust Doctrine says that the government owes stewardship regarding common property resources.
a. need a well informed and supportive public to lay the foundation
for good and protective Instream Flow laws.
Approaches and issues in southeastern states
Southern Division of the American Fisheries Society
AFS members in the Southern Division states were contacted regarding which methods their state uses to determine instream flows. Eight states provided information. The information revealed that some states are still using a single flow statistic (7Q10) which was designed to identify the volume of water needed to meet point discharge water quality thresholds.
The 7Q10 is a flow statistic used to simulate drought conditions in water quality modeling to evaluate waste load allocation. The 7Q10 refers to the lowest average streamflow expected to occur for seven consecutive days with an average frequency of once in ten years and for some streams the 7Q10 flow is zero. The 7Q10 drought flow is inadequate to conserve aquatic life or ecological integrity. For most streams, this flow is less than 10% of the average annual flow and can be expected to result in severe degradation of aquatic communities if it becomes the only flow protected in a stream (Tennant, 1976a, 1976b). The 7Q10 is not an instream flow method. It has often been misused as an instream flow for keeping fish alive.
In some states the state fish and wildlife department does not have the authority to determine instream flows which are set by another state agency. In some states the agency which determines instream flows does not consult with the state fish and wildlife agency regarding what flows are necessary to maintain and enhance viable aquatic resources. There are many beneficial uses including fish and wildlife resources which all compete for the right to use streamflow. Instream flows for fish and wildlife should receive equal consideration as any other request for water allocation. Natural resource managers are faced with the complicated task of protecting and restoring public values while honoring existing uses. To meet this responsibility, managers are challenged to identify appropriate methods to quantify instream flow needs and defend the methods they use and results they obtain. In the absence of a consensus on acceptable protocols and policies, this task has proven difficult for some state fish and wildlife agencies. In 1998 the Instream Flow Council was formed to provide guidance in developing instream flow programs which resulted in the publication Instream Flows for Riverine Resource Stewardship (Annear et. al. 2004).The recommendations contained in that publication comprise the critical elements in this resolution.
Anyone withdrawing more than 100,000 gallons of water per day from any surface or ground water source must get a permit from Georgia’s Environmental Protection Division (EPD). These permits are supposed to be issued only if they do not have “unreasonable adverse effects” on the other water uses in the area, which includes public use and future uses as well as present uses. There are thousands of water permit holders in Georgia, and the collective water withdrawals from each of these users puts a significant strain on our water resources. To prevent adverse effects, permits must include seasonally variable instream flows that are maintained at a point below any water intake location or below a dam, from the headwaters of a river system to the estuaries. All permit applicants must meet these requirements.
During the summer of 1996, the Directors of the Environmental Protection Division (EPD) and the Wildlife Resources Division (WRD) agreed to empanel a multi-disciplinary team of stakeholders to make recommendations on whether EPD’s instream flow protection policy should be modified to specifically provide protection of aquatic habitats and species. The team recommended that EPD employ an interim instream flow policy that allows applicants for new or modified withdrawal permits (for increased withdrawals) flexibility to select from one of three (3) instream flow maintenance options. Current water withdrawal permit holders would not be required to retroactively implement these recommendations. Choices would include:
1) use of a monthly 7Q10 instream flow policy
2) a site-specific instream flow study from which seasonal instream flows would be derived, or
3) one of the methodologies recommended by WRD in its December, 1995 paper entitled A Recommended Method to Protect Instream Flows in Georgia (i.e., on unregulated streams allow the lesser of 30% of the mean annual flow of the stream, or the inflow, to pass the instream withdrawal point; on regulated streams, water supply reservoir releases should be the lesser of 30% of the mean annual flow or inflow during the months of July through November; 60% of the mean annual flow or inflow during the months of January through April; and 40% of the mean annual flow or inflow during the months of May, June, and December).
The team also recommended that the Department of Natural Resources make efforts to conduct and/or require in state, site-specific studies on which to base a final modified instream flow policy to be presented to the Board of Natural Resources for adoption by January 1, 2003. The recommendation further stated that if DNR (or others) have not completed such studies and a final modified policy by January 1, 2003, then the interim modified policy would continue to be employed.
In the winter/spring of 2001 the DNR Board reviewed the 1997 recommendation from the stakeholders’ team and made a policy decision to adopt – with minor modifications and updates – the stakeholders’ document as its own Interim Instream Flow Policy which continues to serve as the statewide policy until a final one is adopted. The Board included this policy decision in its Water Issues White Paper, and instructed EPD to implement this new instream flow policy effective April 1, 2001. The Interim Policy offers three options to permit applicants to maintain adequate flow in streams. The three options include Monthly 7Q10 Miminum Flow option, Site-specific Instream Flow Study option and Mean Annual Flow option.
Point source dischargers in North Carolina have conditions in their permits based on stream flows; permit limits provide wasteload assimilation through effluent dilution and reoxygenation of the stream; all wastewater discharges are required to be treated so that water quality standards will still be met when the stream flow is as low as the 7Q10 . When stream flow falls below the 7Q10, water quality violations may occur. The DWQ sets water quality standards and permit limits, and is responsible for enforcement.
Water withdrawals/offstream uses include water withdrawals for municipal and industrial water supply, agriculture, aquaculture, and golf course irrigation. Structures placed in streams to withdraw water for any purpose may require a permit from the USACE under Section 404 of the Clean Water Act. No instream flow study is required if the water withdrawal for the proposed project is less than 20% of the 7-day, 10-year low flow (7Q10). To avoid cumulative impacts, project developers should still contact the DWQ regarding potential concerns for downstream assimilative capacity and maintaining water quality standards. Withdrawals that are 20% of the 7Q10 or more require additional analysis. The location of the proposed project and the habitat rating of the downstream aquatic habitat will determine whether a desktop analysis or site-specific instream flow study is used to determine the flow. The NC Wildlife Resources Commission does the habitat rating.
A group of water resources and wildlife experts who have reviewed North Carolina's approach to instream flows recommends adoption flow regimes that are driven by the amount of disturbance to the ecological integrity of the stream.
The North Carolina Division of Water Resources in the Department of Environmenta and Natural Resources has put up a page describing their study of and thinking about ecological flow regimes.
South Carolina had a major debate in its legislature in March and April 2008 over instream flows and their relationship to a bill to regulate water withdrawals.
Summary of South Carolina's Approach to Establishing Ecological Flows: 20/30/40 Mean Annual Daily Flow (MADF)
• History of the Approach
Developed in the late 1980’s, this approach aimed to establish the amount of flow that is necessary to support both healthy streams and recreation; the focus was on fish health, not water quality. Three main use categories were considered: navigation, in-channel water coverage, and fish passage.
For navigation, the team considered both recreational and commercial navigation and so used a 14-ft john boat as a reference when determining how much water must remain in the stream to support navigation. They considered that such a boat would require a stream to be 2 ft deep in order to go upstream and 1 ft deep to go downstream and then determined that small, rocky streams (e.g. the upper reaches of rivers) would probably only see one-way boat traffic, while larger streams (e.g. near the coast) would encounter two-way traffic. Finally, they determined that at least 20% of the river width had to meet that guideline (either 1 ft or 2 ft deep) in order to say that the stream could provide for navigation. Upon further investigation, the team found that 20% flow in a river was usually protective of this threshold.
For in-channel water coverage (a.k.a. wetted perimeter), the team compared wetted perimeter to flow volumes by plotting this data on curves and finding the inflection point of each curve. As water is added to an empty stream, the ratio between volume and wetted perimeter is high; at some point, adding additional water to the stream no longer results in an increase in wetted perimeter. This is the inflection point (or maximum benefit point) on the curves; this was the threshold set for in-channel water coverage. The team found that 20% flow was protective of this threshold.
For fish passage, the team used striped bass as the reference and determined that a 20 lb fish would need a channel 18 in deep and 10 ft wide in order to complete their upstream migration. (These criteria were based on the team’s best professional judgment.) The team decided that at least 10% of the stream width had to meet this guideline in order to say that the stream could provide for fish passage. In addition, this guideline had to be met for at least 10 ft long segments along the length of the river, since it is meaningless for the guideline to be met for short, disconnected distances along a stream. In the Piedmont, the team found that 40% flow in a river was generally protective of this threshold. Along the coast, however, they found that 60% flow was needed. The reason for this difference is that in the Piedmont, the main concern is that there be sufficient flow for the fish to swim past rocky shoals, while along the coast the connection of the stream to its floodplain is the critical factor.
The team gathered information from six Piedmont streams and three coastal streams to develop their measurements as to what flow was necessary to meet each threshold.
Although from a science perspective South Carolina Department of Natural Resources (DNR) would prefer site-specific studies, they settled on the 20/30/40 approach as a compromise to provide a level of predictability/certainty for industry. DNR sees this approach as a default, developed for the purposes of a permit program, but feels it is a relatively protective standard.
• Strengths and Weaknesses
A strength of the approach is that it does not set a single standard across the whole state. By using the mean stream flow, the standard (indirectly) takes factors such as climate and soil characteristics into account.
This approach is a very rough tool for determining what makes for a healthy river. To manage our rivers well, we need a less obtuse tool.
This approach is best utilized for small projects. For large projects, a stream-specific study to determine appropriate flow/allocation levels would be better. Such studies could evaluate fish habitat more directly (e.g. by using the IFIM method) and compare this data to the natural hydrograph of the stream (i.e. habitat duration curves).
By its nature, setting minimum flows for the purpose of water allocation permitting effectively initiates a “race to the bottom.” If we determine the minimum amount necessary, then everything but that amount will be permitted for allocation. Instead of asking “how little must we leave in for river survival,” a better question to ask would be “how much should we leave in the river.” Rivers are dynamic systems and need to keep a measure of fluctuation in order to remain rivers. Using a shorter time frame to determine mean flows would be better. Daily or weekly measurements would be great (although perhaps infeasible); even using monthly averages would be better than the current method.
To better account for variability in streams, one change that could be made to the process is to classify streams by type and then establish management goals for each type; some stream types may be fully functional with 20% flow, while others may need 60%, for example. The easiest way to classify streams is based on size, but other options could be considered, such as susceptibility to impairment, primary function (industry, drinking water, T&E habitat), etc.
Additional research is needed on the surface water-groundwater interface in South Carolina. Currently, not much is known about this connection and a better understanding will be critical to setting effective water allocation policy. This issue is not addressed by the 20/30/40 approach. Consider using a percent exceedence flow instead of average annual flow.
Be sure to look at real life situations when establishing policy. For example, an average annual flow level may not normally/naturally be present in a stream in the middle of the summer. When establishing permits, the regulating agency must conduct a point-by-point evaluation of each potential outlet along the stream and determine how much water can be taken out and how much must pass by each point. This decision should not be made at the basin or river level, but considered at each outtake. Similarly, it is important to look at the hydrograph for each stream within the basin, not just the basin as a whole.
Statistically speaking, every river will go below its minimum flow at some point. Therefore, it is critical that the regulatory agency work with the permittee to plan what the permittee will do when the water they need is not present. The permittee needs to have a back-up plan and that must be established up front.
The TN Wildlife Resource Agency is developing an instream flow program. With increasing population growth in Tennessee, there needs to be Instream Flow protection if we are to maintain aquatic species diversity. Water wars have been going on out West for a long time and the Southeastern United States has been experiencing these problems due to the increased demand for water. Currently, the Tennessee Department of Environment and Conservation (TDEC) issues Aquatic Resource Alteration Permits (ARAP’s). One must apply for an ARAP is one wants to make an alteration to a stream, lake, wetland, or river. The Tennessee Department of Environment and Conservation (TDEC) monitors water withdrawals where a quantity activity can lead to a quality impact, such as altering Instream Flow. Water withdrawals are regulated under the Water Quality Control Act.
Tennessee's "INSTREAM FLOW POLICY STATEMENT"
Both the Tennessee Water Quality Control Act and the Tennessee Wildlife Code require that water withdrawal not result in a condition of pollution or harm to aquatic habitat and that resulting Instream Flow provide for the protection of fish and aquatic life. Numerous smaller rivers and streams in Tennessee are no longer suitable for providing sustained water withdrawal for ever-increasing multiple use demand and are, at best, suitable candidates for well-planned water harvesting projects. Examples of sustained multiple use demands exceeding available flow include Doe Creek, Little Pigeon River, Big Creek, Little River, Harpeth River, Piney River, and Green River.
Protection and conservation of fish, aquatic life, and aquatic habitat require that Instream Flow not be less than 20% above the September median flow or 20% above the appropriate multiple of the 7Q10 and reflect the necessary flow regime according to the natural hydrograph of that river due to sustained water withdrawal. Permit applicants proposing to harvest water should provide a water harvest and storage prescription that minimizes negative effects on downstream hydrology, all aquatic life, geomorphology, connectivity, and water quality. Permit applicants proposing sustained withdrawal should provide a proposed Instream Flow Prescription based on an accepted assessment methodology and that the Instream Flow prescription is consistent with the Instream Flow Council’s policy statements.
Reference: Instream Flows for Riverine Resource Stewardship. Instream Flow Council (2004).
Outside the southeastern United States
Issue: New Hampshire has worked long and hard to develop a flow management policy for rivers like the Connecticut in the Rivers Management and Protection Program, that will control the amount of water available for consumptive use during periods of low flow and in the future when the demand for water could be even greater. However, there may be gaps in policy, or inconsistencies between the policies of Vermont and New Hampshire agencies, which need to be addressed. Among them is the question of how Vermont will provide flow management similar to that affecting New Hampshire.
Opportunities: The river flowing between the two states warrants cooperative management by those states, enabled by the federal government and facilitated by the CRJC as coordinators of such policy within the valley. The CRJC, with support from the Environmental Protection Agency, are already pursuing the opportunity to study flow policies on the Connecticut River. The study will identify state and federal policies and regulations that affect flows and appropriate water quality standards, and recommend opportunities for cooperation and policy development.
1. Any flow policies developed for the Connecticut River must maintain water flows at levels which will support the full range of its uses and values.
2. New Hampshire and Vermont should cooperate on an on-going basis in managing the Connecticut River and have coordinated policies on flow management and water withdrawals.
Basins have been divided into groups (by major basins that feed into a common bay). Each bay and basin group has a Basin and Bay Expert Science Team (BBEST) and a Basin and Bay Area Stakeholder Committee (BBASC). The BBASC is charged with balancing the science with other considerations such as human water needs. There is also a state-wide Science Advisory Committee (SAC) that is charged with providing overall direction, coordination, and consistency to the BBESTs. The SAC has prepared a set of papers designed to give direction to the BBESTs. Here is a July 2010 review of the initial approaches suggested by two different BBESTs.
State of Washington
Instream Flow Study Methods used in Washington
The three methods instream flow study methods described below are the primary flow measurement methods used in Washington state. IFIM and toe-width are the methods used most often.
The Toe-Width Method was developed by the Department of Fisheries (WDF), the Department of Game (WDG), and the U.S. Geological Service (USGS) in the 1970s at the request of the state legislature in response to the need to determine minimum instream flows for fish. After the legislature passed the Minimum Water Flows and Levels law in 1969 and the Water Resources Act of 1971, USGS collected water depths and velocities along transects over known spawning areas. WDF and WDG provided the criteria for salmon and steelhead spawning and rearing and the locations of the known spawning areas. After 9 years of data collection, USGS had measured 28 streams and rivers in eastern and western Washington. They had 84 study reaches with each reach consisting of 4 transects. They measured each transect at 8 to 10 different flows. USGS used the data from these 336 transects to calculate spawning and rearing flows for salmon and steelhead. Criteria for the needed spawning and rearing depths and velocities for each fish species and lifestage were used to calculate the square feet of habitat at each measured flow. These points of habitat quantity at different flows were connected to create a fish habitat versus streamflow relationship. Next, these fish habitat relationships were compared to many different variables in the watershed to determine if there were any correlations that could be used to avoid having to do so many flow measurements to calculate a spawning or rearing flow for a certain fish species. The toe-width was the only variable found to have a high correlation. The toewidth is the distance from the toe of one streambank to the toe of the other streambank across the stream channel. This width of the stream is used in a power function equation to derive the flow needed for spawning and rearing salmon and steelhead (Swift, 1976 and 1979).
Instream Flow Incremental Methodology (IFIM)
IFIM generally is selected as the best available method for predicting how the quantity of available fish habitat changes in response to incremental changes in streamflow. The U.S. Fish and Wildlife Service in the late 1970s (Bovee, 1982) developed this methodology. The IFIM involves putting site-specific streamflow and habitat data into a group of models collectively called PHABSIM (physical habitat simulation). Within IFIM are models of fish habitat as affected by hydraulics. The most common model is IFG4, which uses multiple transects to predict depths and velocities in a river over a range of flows. IFG4 creates a cell for each measured point along the transect or cross-section. Each cell has an average water depth and water velocity associated with a type of substrate or cover for a particular flow. The cell's area is measured in square feet. Fish habitat is defined in the computer model by the variables of velocity, depth, substrate, and/or cover. These are important habitat variables that can be measured, quantified, and predicted.
The IFIM is used nationwide and is accepted by most resource managers as the best available tool for determining, in a broad sense, the relationship between flows and fish habitat. However, the methodology only uses four variables in hydraulic simulation. At certain flows, such as extreme low flows, other variables such as fish passage, food supply (aquatic insects), competition between fish species, and predators (birds, larger fish, etc.) may be of overriding importance. In addition to the PHABSIM models, IFIM may include reviewing water quality, sediment, channel stability, temperature, hydrology, and other variables that affect fish production. These additional variables are not analyzed in this report.
After the IFG4 model is calibrated and run, its output is entered into another model (HABTAT) with data describing fish habitat preferences in terms of depth, velocity, substrate, and cover. These preferences vary according to fish species and life-stage (adult spawning and juvenile rearing). The output of the HABTAT model is an index of fish habitat known as Weighted Useable Area (WUA). The preference factor for each variable at a cell is multiplied by the other variables to arrive at a composite, weighted preference factor for that cell. For example: a velocity preference of 1.0 multiplied by a depth preference of 0.9, then multiplied by a substrate preference of 0.8 equals a composite factor of 0.72 for that cell. This composite-preference factor is multiplied by the number of square feet of area in that cell.
A summation of all the transect cells' areas results in the total number of square feet of preferred habitat available at a specified flow. This quantity is normalized to 1,000 feet of stream or river. The final model result is a listing of fish habitat values (WUA) in units of square feet per 1,000 feet of stream. The WUA values are listed with their corresponding flows (given in cubic feet per second).
This methodology was developed by Don Tennant and predicts flows based on average flow. Using USGS data, this method is based on aquatic habitat being very similar when they are carrying the same proportion of the average flows. Ten percent of the average flow is a minimum instantaneous flow recommended to sustain short-term survival habitat for most aquatic life forms. Thirty percent is recommended as a base flow to sustain good survival conditions for most aquatic life forms and general recreation. Sixty percent provides excellent to outstanding habitat for most aquatic life forms during their primary periods of growth and for the majority of recreational uses. In a large river, it can be useful in developing a quick response, such as for evaluating a water right application potential impacts.