The Instream Flow Incremental Methodology

Transcription

1 The Instream Flow Incremental Methodology Introduction to IFIM Scientific support for complex management decisions involving water use and impacts to aquatic systems requires a better understanding of critical instream flow and habitat needs. In the early 1980's, scientists at the U.S. Geological Survey (USGS) Fort Collins Science Center (FORT) set out to answer those questions and developed the Instream Flow Incremental Methodology (IFIM). IFIM is now in use worldwide, IFIM is a decision-support methodology that provides a comprehensive technical framework for addressing the streamflow needs of fish and other living organisms within a river system Instream flow requirements are the amount of water necessary to sustain instream values at acceptable levels. Instream values are the uses made of the water within the stream. These include such values as fish and wildlife needs, river-based recreation, navigation, hydroelectric generation, wastewater assimilation, and fresh water for estuaries. As the need for incorporating biological objectives into water management decisions has grown, so has the need for methods and metrics to incorporate predictions of relevant biological responses into an increasingly complex decision environment that attempts to balance multiple uses. This task involves the integration of a variety of models including, but not restricted to, spatially explicit habitat responses for aquatic biota, water temperature, habitat connectivity, reservoir operations, water allocation, flow routing, 2-d hydraulics, spatially explicit habitat responses for aquatic biota, water temperature, sediment transport, water deliveries and exports, and flood frequency and magnitude. In most cases, the IFIM analysis framework combines a subset of these models such as 2-d hydraulics. In many cases stream hydraulics, habitat use criteria, and hydrology data are the primary drivers for analysis. Ideally, several aspects of the impacts of water management are integrated for Federal land managers and others. The general approach for model integration is to develop customized decision-support systems that link outputs from the numerous types of models described above and organize the results over time in a control and treatment comparative format. The ownership of the resulting product is transferred to Federal and other water and aquatic resource managers to help them predict the impacts of different management alternatives over multiple time and spatial scales.

2 This is likely to involved and time consuming for the Rosemont Mine Project. In addition, the Cienega Creek, Empire Gulch and other waters have surface water elevations (less than 1 foot or 0.3 meters) that only allow for very small increments of change before the system will no longer support flowing water in springs and streams. This proximity to no flow conditions may allow for a simplified approach as changes in habitat quality are not likely to be subtle. Example Project with Applicability to Rosemont GW Impacts An example of application of the IFIM process is found in Miller ( Quantification of flowhabitat requirements for aquatic species in the San Pedro River, through the San Pedro National Conservation Area). Studies were conducted on the San Pedro River through the San Pedro Riparian National Conservation Area (SPRNCA) for BLM to determine changes in habitat availability for fish in the San Pedro River as a function of changes in streamflow. The study provided a framework for assessing changes in physical habitat in the river as a function of flow for the species of interest and to provide a tool to assess streamflow needed to preserve and enhance the aquatic species in the SPRNCA. This type of study is applicable to flowing waters on the LCNCA. For lentic waters sophisticated hydraulic modeling is not required. Surface are or wetted perimeter of the pond bottom may suffice. This study included an analytical model that combines 2-dimensional hydraulics, a GIS habitat model, and hydrologic data to produce a habitat time series. This approach follows the concepts of the Instream Flow Incremental Methodology (IFIM) (Bovee 1982, Bovee et al. 1998). The study combined stream hydraulics, habitat use criteria, and hydrology data for analysis and San Pedro River study sites. The approach for assessing instream flow needs for fish utilized hydraulic analysis and habitat modeling in a modified IFIM to evaluate changes in quantity, quality, and distribution of habitat with changes in flow in several reaches of the San Pedro River Data needed for the study and process physical Hydraulic modeling begins with construction of a digital terrain map for the study area. A survey-grade Global Positioning System (GPS) was used to field map each study site Data points obtained were used to construct a detailed topography map (or grid) of the channel and adjacent floodplains and terraces Multiple data sets of water-surface elevations and point velocity measurements were used to calibrate a two-dimensional hydraulic model to simulate depth and direction of flow through each site.

3 A grid is created of flow depths and velocities is then compared to habitat preference criteria for species of interest to determine location and quality of fish habitat for each species and life stage The habitat modeling for this analysis followed the concepts of IFIM and the computer simulation steps of the Physical Habitat Simulation System (PHABSIM). Other models are available that may be better. IFIM requires hydraulic data and simulations; habitat use data expressed as habitat suitability criteria and hydrology data for a range of stream discharge conditions. Data needed for the study and process fish habitat Habitat modeling requires information on fish utilization of certain depths and velocities of flow, in addition to utilization of certain substrate, cover, and other channel conditions. Habitat utilization values were compiled from existing data sets from elsewhere in the San Pedro River Basin and new data collected within the SPRNCA. The habitat suitability functions (depth and velocity) were then used as a filter for the grid of depth and velocity values modeled to estimate suitability of habitat in each grid cell at the site The area of grid cells with suitable habitat were then summed to obtain total usable area for a given streamflow level in the entire reach Habitat suitability modeling for each species of interest is accomplished in an ArcView GIS analysis Multiple layers of usable habitat were generated, corresponding to each species, life stage, and flow of interest at specified flow rates (see figures below) Time series analysis for fish habitat relative to changes in monthly flow The habitat discharge relationships are theoretical functions based on channel shape, hydraulics, and habitat use of a given species and life stage. These relationships for each study site are used as input data for the habitat time series (median monthly flows). Summation of total habitat for each species and simulated flow resulted in a habitat-flow relationship by species and lifestage that becomes input for the habitat analysis at different base flows. The habitat versus discharge relationships were input to a computer spreadsheet and combined with median monthly flow rates to calculate habitat over time Out Puts for Decision Making The amount of area within the study site that matches a particular species habitat preference are determined for a specified flow rate.

4 Generally, the habitat time series is the decision point in IFIM. Habitat time series produces the data needed to compare a range of flow conditions over time and to compare different flow management scenarios The relative abundance of habitat conditions over a period of time is an integral part of the comparison of flow regimes. The final step is a comparison of flow habitat relationships using a time series of flows for each study reach. This analysis allowed a comparison between the existing flow regime and the altered flow regime to determine habitat available with each flow rate. Below are outputs that were used in the Miller (2006) study for making management decisions. The time series graph is by month. For the Rosemont Mine Project, it would be more relevant to compare results for flow changes that occur decades or centuries into the future.

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6 Flow is 0.0 cfs Flow is 0.0 cfs

7 Resources required to pursue an IFIM study on the LCNCA Time required for conducting a simple IFIM study on Cienega Creek and Empire Spring is rather speculative until a study plan is developed. An educated guess would be 1 day for 2 people per site for data collection. An additional day may be required for trouble shooting field work as conditions are challenging in some locations. Time to do the modeling may take a month or more for 1 person assisted by other knowledgeable individuals. Sophisticated GPS receivers and other equipment will be needed. Sources: FT Collins Science Center (USGS) Water Management Studies Research Task: RB00CM8.1.0 Chris Holmquist-Johnson Miller, W Quantification of flow-habitat requirements for aquatic species in the San Pedro River, through the San Pedro National Conservation Area. Miller Ecological Consultants, Inc., Ft. Collins, Colorado.