Environmental+flows

**Incorporating Environmental Flows Into River Restoration**  //by Ryan Morrison// **Introduction**  Rapid human population growth, increased management of water resources, and the expansion of urban areas into natural environments are straining riverine systems around the world. Historically, humans have managed these riverine systems to provide a dependable supply of water for consumptive use. However, in the past half-century studies have shown natural flows to be important for maintaining geomorphologic processes (Doyle et al., 2007), aquatic biodiversity (Bunn and Arthington, 2002; Hynes, 1970), riparian plant communities (Nilsson and Svedmark, 2002), and other important riverine ecological processes (Poff and Zimmerman, 2010), leading to the development of techniques for determining environmental flow requirements. Tools for providing environmental flows are now readily available for scientists and engineers to utilize during river restoration planning and have been applied in systems around the world. The objectives of this paper are to 1) examine the historical evolution of environmental flows as it pertains to restoration efforts, 2) describe the most important components of environmental flow development and their scientific basis, and 3) provide a contemporary case study of an environmental flow methodology applied to the Rio Chama, New Mexico. Important components of environmental flows, particularly as they related to the natural flow regime of a river, will be highlighted with particular emphasis on those easily applicable to restoration projects. An examination of restoration efforts currently underway on the Rio Chama, a major tributary to the Rio Grande in northern New Mexico, will provide contextual support for how one specific environmental flow technique—the Indicators of Hydrologic Alteration (IHA) methodology—can be applied to a river system. A final discussion will postulate the direction of environmental flow science for the next few decades as climate change and declining water availability restricts restoration flexibility. **Brief History of Environmental Flow Development**  Until the later half of the twentieth century, water management strategy focused almost exclusively on providing adequate water for human needs. This focus began to shift in the 1960s as worldwide concern for protecting biodiversity and sustaining environmental systems permeated water resource policy. Research on the physical processes of running water and the riverine ecology became intricately linked (Hynes, 1970). The first substantial environmental flow (sometimes referred to as instream flow or e-flow) standards were developed in the late 1970s as pressure for minimum flow requirements needed for water permits under the Clean Water Act threatened fisheries (Petts, 2009). Abstraction limits were set to ensure enough water was present throughout specific periods of the year for fish survival, but even these standards were based on professional judgement rather than scientific evidence (Fraser, 1972). Orsborn and Allman (1976) presented the need for a more holistic consideration of flows for fish, recognizing the importance of flow variability in a river system. Hence, the modern idea of environmental flows was born—the idea that river environments are dynamic systems in which aquatic species have evolved, and ensuring the natural variability of the system is vital to protecting river ecosystems (Poff, 2009; Poff et al., 1997; Postel and Richter, 2003). The Instream Flow Incremental Methodology (IFIM) was widely adopted in the 1980s. The IFM approach allowed researchers to quantify river habitat as a function of discharge (Stalnaker et al., 1995). According to Bovee (1982), an original developer of the IFIM processes, the primary “decision variable generated by IFIM is total habitat area for fish or food organisms.” A popular component of IFIM is Physical Habitat Simulation (PHABSIM), in which specific habitat attributes are linked to life stages of various aquatic species (commonly fish) (Annear et al., 2004). The discussion on physical habitat in stream restoration describes the IFIM and PHABSIM methodologies in more detail. Environmental flow methodologies proliferated in the 1980s and 1990s. The most notable contributions to the field were the Indicators of Hydrologic Alteration (IHA) methodology (Richter et al., 1996), Range of Variability (RVA) methodology (Richter et al., 1997), and the concept of the '//natural flow regime'// (Poff et al., 1997). The IHA method compares the hydrology of a reference “pre-development” scenario to a “post-development” scenario and calculates 32 hydrologic alteration parameters based on important flow variability indictors. The indicators represent common metrics such as median monthly flow, temporally-averaged minimum and maximum flows, hydrograph fall and rise rates, and low or high pulse discharges. The RVA method uses IHA outputs and compares the frequency of occurrence of the same parameters. The RVA method allows researchers to determine how often a specific parameter in the “post-development” scenario falls within the same statistical quantile as the “pre-development” data. Both the RVA and IHA methodologies can be modeled using the Indicators of Hydrologic Alteration Software developed by The Nature Conservancy (The Nature Conservancy, 2009a). The natural flow regime concept is the foundation for the IHA, RVA, and other methodologies developed since. Poff et al. (1997) explains that the natural flow of a river varies on different timescales and can be characterized using the following groupings: magnitude, frequency, duration, predictability, and rate of change. Each of these groupings are important to consider when restoring or protecting a river environment. King et al. (2003) presented the Downstream Response to Imposed Flow Transformation (DRIFT) methodology as a holistic approach for advising environmental flow development. The underlying philosophy of DRIFT was that major abiotic and biotic components need to be accounted for when successfully managing a river ecosystem, and, therefore, the full spectrum of flows, and their temporal and spatial variability, need to be managed as well. The Ecological Limits of Hydrologic Alteration (ELOHA) approach is a popular contemporary environmental flow methodology. The ELOHA framework is designed to allow regional-scale development of environmental flows, and is composed of four main steps: 1) compiling or developing hydrologic base data, 2) classifying and grouping similar river basins, 3) calculating flow alterations for post-development conditions, and 4) developing flow- ecological connections (Poff et al., 2010). Adaptive management is also an important component of managing and improving environmental flow recommendations. The importance of environmental flows is now well established, but the institutional adoption of environmental flow standards is lagging behind the science. Furthermore, there is a wide gap between the recognition of natural flow needs and data needed to support flow-ecology linkages (Poff et al., 2010). Future advancements of environmental flow methodologies will rely on strengthening our understanding of flow-ecology interactions and incorporating adaptive management into environmental flow implementation. **What to Consider //Before// Development of Environmental Flows**  It is easy to jump into the technical aspects of setting enviornmental flows without first considering other important components of an environmental flow study. Before any modeling efforts occur, considerations such as the study approach, study scale, and resource availability should be determined. These considerations will keep an environmental flow study within budget and on-track to a successful completion. **Objective vs. Scenario-based Approaches**  Recognizing the driver of an environmental flow study is important to do before setting goals for a project. A project with a specific ecological goal, such as to flush more sediment from a river, will produce different results than one without a central driver. Acreman and Dunbar (2004) define two different approaches for setting environmental flows. An objective-based approach uses specific ecological, economic, or social goals to drive the determination of environmental flows. For example, managers might want to inundate a pre-defined area of floodplain each year for flood-recession agriculture. Developing flow recommendations that allow the correct area of farmland to be flooded would be the primary focus of such a study. This approach has well-defined objectives in contrast to the scenario-based approach, which studies multiple tradeoffs between various alternatives. A scenario-based approach balances human and environmental flow needs by examining a range of alternatives. Setting flow standards for developed basins often requires a scenario-based approach to juggle the needs of water delivery, hydropower, recreation, and the river environment. **Scale of Study**  Rivers function at various spatial and temporal scales. Environmental flow studies should consider at which scale restoration efforts should be focused before beginning a project. Spatial scales include micro-, meso-, and macrohabitats nested within landscape features, such as reaches, segments, and watersheds (Annear et al., 2004). The discussion of physical habitat describes the attributes of each habitat scale. Understanding the ecological controlling factors at each scale is important for a sucessfull project. River segment or watershed scales might be appropriate for influencing sediment transport within a system, whereas a reach scale may be useful when determining flows to improve benthic macroinvertebrate community health. Changes in river processes over different temporal scales are also important to consider during environmental flow studies. Different components of a river system respond at varying rates (Petts, 1987). The length of temporal scales is generally inversly proportional to the size of the spatial scale; watershed changes may take decades to occur (see the discussion on fluvial geomorphology) while microhabitats shift daily (Annear et al., 2004). **The Importance of the Natural Flow Regime**  Modern techniques for developing environmental flows, such as ELOHA, recognize the importance of the natural flow regime to sustain a river’s ecological health. There is agreement among scientists that the natural flow variability of a system should be maintained or replicated to protect the biodiversity and ecological services of a river system (Arthington et al., 2006). The important hydrologic components in a system include magnitude, frequency, timing, duration, rate of change, and predictability of flow events (Poff et al., 1997). The natural flow regime is important for many aspects of aquatic ecological health including water quality, energy sources, physical habitat, and biotic interactions (Figure 1). Not only do these facets of the natural flow regime sustain different ecological niches in a system, but each species in a riverine system evolved based on the characteristics of the naturally occurring flow regime. How each component of the natural flow regime can affect riverine ecology, and why it is important to consider flow variability in river restoration, is examined.

The timing of specific flow events, such as spring runoff or monsoon storms, is important for aquatic and riparian ecology. When the natural timing of riverine flows is disrupted (such timing shifts in peak flows due to hydropower production), common aquatic responses include a disruption of fish spawning cues, decreases in reproduction and recruitment, and a change in diversity and community assemblages. Riparian communities can also be altered due to changes in timing. Examples include reduced riparian recruitment, reduced plant growth, and an invasion of exotic plant species (Poff and Zimmerman, 2010).

Flow magnitudes are also important for maintaining aquatic and riparian communities. The loss of extreme high or low flows, often caused by the introduction of dams, can alter species assemblages, increase the abundance of non-native species, and cause the upland species to encroach the riparian corridor. An increase in high flow magnitudes, can literally wash away species not accustomed to such high flows and reduce species richness (Poff and Zimmerman, 2010).

A change in frequency of peak flows has been shown to negatively influence reproduction rates, decrease habitat for young fishes, and shift community compositions (Poff and Zimmerman, 2010).

A decrease in flow duration can cause floodplains to be inundated for a shorter time period than usual. Many fish species depend on floodplain inundation for access to energy sources, and some riparian communities rely on inundation for new plant recruitment. A decrease in the the duration of inundation can cause reduced area of riparian cover, change in fish assemblages, and an increase in non-native species (Poff and Zimmerman, 2010).

Finally, the rate of change of riverine flows can decree the germination survival of riparian communities, reduce benthic macro-invertebrate diversity, and disrupt the abundance of energy sources available to fish communities (Poff and Zimmerman, 2010).

When designing a restoration project, it is important to understand how the natural flow regime has been altered and the corresponding ecological effects of this alteration. Restoration efforts that do not account for changes in the flow regime may not be successful. For instance, it may not be possible to establish native riparian vegetation if the plant physiology does not respond to the altered hydrologic conditions. Similarly, bank stabilization efforts may fail if the magnitude of peak flows has increased in the system. Tools, such as the Indicators of Hydrological Alteration (IHA) software, can be used to compare various components of the flow regime and determine the largest hydrologic changes within a system. Restoration teams can use IHA data to pinpoint the greatest hydrologic changes in a system and formulate restoration goals accordingly.

The following case study of the Rio Chama, located in northern New Mexico, illustrates the use of IHA software to analyze changes in flow regime. **Rio Chama Case Study**  Reservoir operations and flow augmentation have altered the hydrology of the Rio Chama during the past century. The three dams in the basin—El Vado, Abiquiu, and Heron Dam—are managed for water delivery and recreational rafting needs, and the San Juan-Chama Project increases basin yield by approximately 110,000 acre-feet every year (Figure 2). To better understand the effects of water management on the Rio Chama, multiple IHA analyses were performed using available [|USGS gage data] in the basin. IHA analyses are used to quantify changes of common hydrologic parameters, such as median monthly flows, hydrograph rise/fall rates, and maximum/minimum flows. The combined effects of water management operations, as well as the isolated effects of the San Juan-Chama Project and rafting releases, were examined. <span style="display: block; font-family: Arial,Helvetica,sans-serif; font-size: 12pt; text-align: left;">**Methodology**  The Indicators of Hydrologic Alteration (IHA) software developed by The Nature Conservancy was used to analyze changes to Rio Chama hydrology due to various management decisions (The Nature Conservancy, 2009a). Based on concepts developed by Richter et al. (1996, 1997), the IHA software calculates statistical parameters to compare changes in hydrology (The Nature Conservancy, 2009b). A total of 33 IHA parameters are represented by five general groups: magnitude of monthly flows; magnitude and duration of annual extreme water conditions; timing of annual extreme water conditions; frequency and during of low and high pulses; and rate and frequency of water condition changes. Each parameter is calculated for pre-development (hereafter defined as unaltered) and post- developed (hereafter defined as altered) hydrologic datasets. In addition, IHA software uses the Range of Variation Approach (RVA) (Richter et al., 1997) to compare natural variations of an IHA parameter between unaltered and altered hydrologic conditions. <span style="display: block; font-family: Arial,Helvetica,sans-serif; font-size: 10pt; text-align: left;"><span style="display: block; font-family: Arial,Helvetica,sans-serif; font-size: 10pt; text-align: left;">**System Hydrology**  Daily flow data from USGS gage 08285500 ([|El Vado gage]), located downstream of El Vado Dam, were used to represent altered hydrologic conditions (period of record 10/30/ 1935–01/01/2012). Because flow data prior to the construction of El Vado Dam (completed 1935) are not available, data from USGS gage 08284100 ([|La Puente gage]), located 15 river miles upstream of the dam near the town of La Puente, were used to represent unaltered conditions (period of record 10/01/1955–01/01/2012). Although irrigation diversions occur upstream of the La Puente gage, the effects were assumed to be relatively minor compared to operations of El Vado Dam. Willow Creek and Boulder Creek are tributaries that enter the Rio Chama between the La Puente and El Vado gage locations. Both creeks are ephemeral systems that primarily convey snowmelt and monsoon flows. The San Juan-Chama Project (SJC Project), implemented in 1971 to fulfill obligations of the [|Colorado River Compact] (Glaser, 2010), uses Willow Creek to transfer approximately 110,000 acre-feet per year from the San Juan River in the upper Colorado River basin to the Rio Chama. Water from the SJC Project is stored in Heron and El Vado Reservoir and typically released during the summer irrigation season. A water balance analysis was performed using USGS gage data to determine the volume of additional water entering the Rio Chama between the La Puente and El Vado gages. During a 15-year period between 1955 and 1970, discharge from Boulder Creek and Willow Creek accounted for 3% and 5% of the cumulative volume of water at the El Vado gage. The remaining 92% of volume was represented by discharge at the La Puente gage (Table 1). Because flow magnitudes from Willow Creek are significantly attenuated due to reservoir operations, and historical discharge volumes were small compared to those in the Rio Chama, modifications to the La Puente gage dataset were assumed unnecessary. Table 1. Contribution of flows below El Vado Dam

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 10pt;">**IHA Analysis** Multiple analyses were conducted to examine the effects of specific management conditions on the system. Flow data from 1957–2010, the longest overlapping period of record for the El Vado and La Puente gages, were used to examine the combined effects of water management on the Rio Chama. The effects of the SJC Project (implemented in 1971) were examined through two separate analyses—a pre-SJC Project analysis (1957–1970) and post-SJC Project analysis (1971–2010). Similarly, consequences of recreational rafting releases (implemented in 1985) were examined through two analyses—a pre-rafting analysis (1971–1984) and post-rafting analysis (1985–2010). The starting date for the pre-rafting analysis was set to 1971 so that SJC Project releases were included in both the pre- and post-rafting records. Relevant information for each analysis is found in Table 2. The analyses assumed hydrological datasets had a non-normal (skewed) distribution, and that high/low pulse thresholds were plus or minus 25 percent of the median flow. The RVA calculations assumed the range of flows was split into equal tertiles (plus or minus 17 percent of the median). Table 2. Period of record for each IHA analysis

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 12pt;">**Case Study Results** To examine the effects of different water management operations on the Rio Chama, analyses were grouped into three scenarios. First, IHA calculations were performed for the longest overlapping period of record contained in the El Vado and La Puente discharge datasets. These calculations corresponded to 55 years of flow data between 1956 and 2010. Second, to study impacts of the SJC Project on Rio Chama hydrology, pre- and post-SJC Project analyses were conducted for the years 1957–1970 and 1971–2010. Third, effects of weekend rafting releases from El Vado Dam were examined by performing two additional analyses for the years 1971–1984 and 1985–2010. Important results are summarized in this report, but output files from the analyses can be found in the appendix. Figure 3 shows altered and unaltered hydrographs between 1956 and 2010, and delineates the pre- and post-SJC Project analyses and pre- and post-rafting analyses. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 10pt;">**Overall Effects of Management Operations** An analysis of hydrology alterations between 1956 and 2010 (Table 3) revealed that major impacts due to water management operations included increases in median flows, increases in various temporally-average minimum flows, decreases in temporally-averaged maximum flows, and greater hydrograph rise/fall rates. These results were expected considering the augmentation of flows in the basin due to the SJC Project and a compression of the natural hydrograph due to dam operations. The mean annual flow increased from 347 cfs to 432 cfs, and median flows for all months increased except in April and May (see Figure 4 as an example of median August flows). Storage of spring runoff in preparation for summer water deliveries are likely the cause of lower flows in April and May, and flow augmentation caused increases in median monthly discharges. In addition, 1-, 3-, 7-, 30-, and 90-day minimum flows all increased during altered hydrological conditions. Maximum flows decreased for the same temporal-averaged periods. The increase of temporally-averaged minimum flows, and corresponding decreases in maximum flows, are indicative of reservoir operations in the basin. Table 3. IHA results of overall effects from management operations on the Rio Chama



The number of low pulse flows on the Rio Chama—the low pulse threshold was defined as the 25 percentile flow—decreased from seven to two under altered hydrological conditions. Conversely, the number of high pulse flow—defined as the 75 percentile flow— increased from three to seven during altered conditions. The overall shape of the typical hydrograph in the system was also affected. The median rise rate increased from 9 cfs/day to 16.5 cfs/day, and the median fall rate decreased (indicating a faster decline) from –9 cfs/day to –17.5 cfs/day. Finally, the dates of the annual one-day minimum and maximum flows were shifted to later in the year by 25 and 9 days, respectively. The RVA analysis supported the IHA parameter calculations. Using unaltered flow data, the number of values for each parameter was separated into tertiles. The change in variation for each parameter using altered flow data is indicated by a positive or negative hydrologic alteration value. Figure 5 reveals how each parameter shifted within the natural variation of values based on unaltered hydrologic conditions. The values associated with median monthly flows shifted into the top tertile, except during April and May. Minimum and maximum flows shifted into the top and bottom tertiles, respectively. Low pulse counts occurred more frequently in the bottom tertile, and high pulse counts were shifted to the top tertile. Typical hydrograph rise and fall rates had positive hydrologic alteration values in the top and bottom tertiles.

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 10pt;">**Effects of the San Juan-Chama Project** Two IHA analyses were performed to examine the effects of SJC Project diversions to the Rio Chama. The pre-SJC Project analysis used a period of record from 1957–1970, and the post-SJC Project analysis extended from 1971–2010. Prior to the implementation of the SJC Project, alterations to the natural flow regime primarily resulted from El Vado Dam operations. The major impact of the SJC Project has been an increase in flow volume within the basin. A comparison of the two analyses reveals that mean annual flows have increased by nearly 30%, and median summer flows have considerably increased since the implementation of the SJC Project. June, July, and August flows increased by nearly 500% resulting from the trans-basin delivery of water. The pre-SJC Project analysis showed that median flows varied between –25% to +90% of unaltered values. Minimum flows increased for all temporally- averaged periods following SJC Project implementation, while only the 30- and 90-day minimum flows increased prior to the Project. Maximum flows decreased during the post-SJC Project period by up to 30%, contrasting sharply with a maximum flow decrease of up to 120% before the augmentation of water. The high pulse count increased during both periods. However, the low pulse count decreased during the post-SJC Project time frame and increased during the pre-SJC Project period. The implementation of the SJC Project had a considerable effect on the reversal rates of the hydrograph. The rise and fall rates for the post- and pre-SJC Project periods increased by up to 200% and 35%, respectively. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 10pt;">**Effects of Rafting Releases** Releases from El Vado Reservoir are increased during summer weekends to provided adequate flows for recreational and commercial rafters. Discharges near 600 cfs are typically maintained through weekends, and are reduced by up to half during the rest of the week, depending on water delivery schedules. The practice of releasing rafting flows began in 1985 after an agreement between the [|Albuquerque Bernalillo County Water Utility Authority] and the [|Middle Rio Grande Conservation District]. Two analyses were performed to determine the effects of summer rafting flows in the Rio Chama. The pre-rafting analyses used a period of record from 1971–1984, and the post-rafting analysis extended from 1985–2010. The pre-rafting analysis starts in 1971 so that effects of the SJC Project are included in both the pre- and post-rafting analyses. Because operations for rafting cause rapid increases and decreases in river stage, the IHA analyses focused on the identification of flow pulses above 600 cfs. Prior to years when rafting flows were implemented, the median occurrence of flows greater than 600 cfs was 5.5 per year, and the median duration was 8.5 days. After rafting releases were implemented, the median occurrence of flows greater than 600 cfs increased to 8.5 per year with a median duration of 3 days (Figure 6). The contrast in high pulse count and duration between pre- and post-rafting release periods is assumed to be indicative of water delivery management. Before 1985 water deliveries were made with few high-flow releases that lasted for extended durations. After rafting discharges were implemented, a greater volume of water deliveries were made with frequent, high-pulse releases that benefited the rafting community.

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 12pt;">**Case Study Conclusion** The IHA analyses show how Rio Chama hydrology has been altered due to management efforts on the river. The combined impacts of management efforts include the “squashing” of the river’s natural hydrograph—low flows have increased and high flows have decreased—caused by reservoir operations, an increase in median monthly flows due to SJC Project water deliveries, and more rapid hydrograph rates-of-change resulting from rafting releases. Future work will focus on connecting the IHA results to ecological conditions in the river, and developing hydrologic scenarios (within the constraints of current management needs) that benefit various ecological processes, such as sediment transport and riparian habitat recruitment. **<span style="font-family: Arial,Helvetica,sans-serif; font-size: 14pt;">Climate Change and Environmental Flows ** Modern environmental flow science treats past hydrologic conditions as the ideal standard when pursuing restoration efforts. However, this approach assumes that the same environmental conditions which influenced past hydrologic conditions will not change. Climate change studies have presented clear evidence that future hydrologic conditions will //not// remain the same, and that our water resources management strategies will require adjustment. In much of the United States<span style="font-family: Arial,Helvetica,sans-serif; font-size: 10pt;">, climate change is expected to cause more winter precipitation to occur as rain, a shift in snow melt to earlier in the year, and an increase in spring season flows while decreasing summer flows (Barnett et al. 2008). The natural flow regime of many systems will be altered, leaving river restoration teams uncertain whether to use historical records as a proxy for future planning efforts. And, because climate change will affect restoration efforts in unknown ways, many wonder why we should spend money on restoration at all. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 10pt;">Seavy et al. (2009) argues that river restoration projects become even more important as climate change begins to affect our ecological systems. Many ecosystem systems are naturally resilient and are able to buffer environmental changes. For instance, riparian systems create thermal refugia for wildlife, provide aquatic-terrestrial linkages, and provide linear habitat connective, all of which are important for adapting to climate change (Seavy et al., 2009). Therefore, maintaining environmental flows in our natural systems is crucial for sustaining ecosystem function as these systems are threatened by both climate change and anthropogenic influences. **<span style="font-family: Arial,Helvetica,sans-serif; font-size: 14pt;">Conclusion ** The study of environmental flows is evolving. Contemporary techniques, such as ELOHA and IHA (demonstrated in this paper), have allowed strong progress in the discipline. Still, climate change, improved scientific techniques, and management policies will likely be the drivers of future environmental flow innovation and improvement. Recognizing that sustainable water management includes protecting ecological water needs will continue to be the foundational principle of environmental flow science as the field develops. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 14pt;">**References** Acreman, M., Dunbar, M. J., 2004. Defining environmental river flow requirements — a review. Hydrology and Earth System Sciences 8 (5), 861–876. Annear, T., Chisholm, I., Beecher, H., Locke, A., Aarrestad, P., Coomer, C., Estes, C., Hunt, J., Jacobson, R., Jöbsis, G., Kauffman, J., Marshall, J., Mayes, K., Smith, G., Wentworth, R., Stalnaker, C., 2004. Instream flows for riverine resource stewardship, revised edition Edition. Instream Flow Council, Cheyenne, WY.

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