The methods used to measure the various habitat parameters in this inventory were based on those established by government agencies and experts in pertinent fields, and were modified where appropriate to fit the unique conditions at the study sites. Numerous specialists were involved in developing and evaluating the inventory methodologies, including Dr. Bruce Roundy, Dr. William Shaw, and Dr. Guy McPherson (University of Arizona); Dr. Waite Osterkamp and Dr. John Parker (U.S. Geological Survey); and Dr. Bill Halvorson (U.S. National Biological Service).
Measuring channel geometry features allows streamflow characteristics to be determined indirectly based on channel characteristics formed by the water and sediment discharge of a stream (Hedman and Kastner 1977, Hedman and Osterkamp 1982). Generally, an alluvial channel's size is indicative of the water conveyed through it, and its shape is largely the result of the sediment transported along it by the stream (Hedman and Osterkamp 1982). Conducting a baseline survey of the existing physical conditions of a stream channel enables changes in the character of the stream to be monitored (Harrelson et al. 1994).
The physical characteristics of the Rincon Creek channel at each of the four study sites were surveyed in order to monitor changes in channel cross-sectional geometry and gain information on sediment movement through future inventories; and to determine the cross-sectional area of the active channel in order to calculate peak discharges (see Crest Stage Gauges below). Data collection procedures and location of transect lines for measuring cross-sectional profiles followed methods described in Hedman and Kastner (1977), Hedman and Osterkamp (1982), Gordon et al. (1992) and Harrelson et al. (1994).
Three transect lines were established at each of the four sites by stretching a measuring tape tightly across and perpendicular to the low-flow channel. Three cross sections were surveyed at each site because the channel dimensions of width and average depth may vary along the channel. Transects were numbered sequentially in the downstream direction. The tape was extended to include a significant portion of the floodplain; transect length therefore varied between and within sites according to terrain, vegetation characteristics, and property ownership. The position of transects along the length of the study sites was randomly determined within the constraints imposed by a combination of factors including study site length, channel pattern characteristics, general streamside plant community patterns, and the extent of anthropogenic disturbances. To avoid changing the drainage area, transects were not placed immediately upstream or downstream from tributaries. Since vegetation data were also collected along the transects, they were placed at least 40 m apart so that vegetation sample plots would not overlap (see Plant Community Inventory for diagrams illustrating the location of transects and plots at each site). Study Site A was the exception to these guidelines. In order to reflect the site's more varied topography and plant communities, five transects placed at 20 m intervals were established.
Cross-sectional profiles were measured using a transit (a surveyor's level), a leveling rod and a measuring tape. Elevation readings were taken at numerous locations along each transect: all significant breaks of slope in the channel, as well as the active floodplain, bankfull elevations and stream terraces, were measured (see Channel Morphology Data Collection Form in Appendix). Cross-sectional area of the active channel was calculated using Aquapac software (developed in Australia to facilitate the calculation of various parameters associated with stream environments).
To ensure relocation of transects for future inventories, permanent endpoint monuments were installed at both ends of each transect, and their locations determined with a Global Positioning System (GPS) receiver. The GPS coordinates of each transect monument were included in the database described below in the Geographical Information System section. Photographs of the tapes stretched across the channel along each transect line were also taken.
Streamflow characteristics are extremely significant factors in determining the overall health and trend of riparian ecosystems. Collection of streamflow data is important for evaluation of the long-term water supply needed to maintain riparian vegetation. In addition, floods rearrange streambed habitats, producing ideal seedbed conditions for riparian plants. Relating discharge data with the form of the channel delineates over-bank flow frequency (Briggs 1996). These intricate interrelationships between riparian ecosystems and stream hydrology make the inclusion of stream hydrology in a riparian monitoring program mandatory.
For this study, six crest stage gauges were installed to measure streamflow, three at Study Site B and three at Study Site C. Crest stage gauges measure the flood crest under conditions of transient flow. Gauge design, installation and placement followed procedures outlined in Boyer (1964), U.S. Geological Survey (1977), Gordon et al. (1992) and Harrelson et al. (1994).
Gauges were installed in the low flow channel 200 m from one another, and their locations in relation to the permanent cross-sectional transect lines at each site were noted. Photographs of the gauges were also taken to aid in relocation. The gauges were made of 4-ft-long, 3-in-diameter PVC pipes with open, screened bottoms and vented tops that were mounted vertically on 4 in x 6 in x 10 ft posts buried in the channel to a depth of 6 ft (Fig. 3). The posts were set in 160 lbs of concrete, and were beveled on the upstream side to reduce friction and debris accumulation during flow. Each gauge contains a removable 1 in x 1 in x 4 ft wood staff wrapped with an adhering cloth and held in place by a cap on the pipe. Finely ground styrofoam pieces are placed at the bottom of the PVC pipe, where they are retained by the screen. When a flood wave passes, the water rises through the screen and lifts the styrofoam (as well as silt and other material); when the water recedes, the styrofoam is left clinging to the staff at the crest stage.
The gauges were checked after every large precipitation event. Any flood-crest marks were measured and recorded. The current elevation of the channel bed surface relative to a reference elevation marked on each gauge was also measured. Each gauge was reset after every peak flood event by removing all debris from the staff and restocking the styrofoam pieces as necessary (see Crest Stage Gauge Data Collection Form in Appendix).
Peak discharges at Study Sites B and C were estimated using methods described in Gordon et al. (1992) and Briggs (1996). The slope of each flood peak was obtained by measuring the elevation of the flood-crest mark relative to the established reference elevation on each gauge. Using Manning's equation, instantaneous discharge was calculated for the two reaches. This was accomplished by combining slope data (developed from the gauges) with a roughness coefficient and the cross-sectional area at the gauge site (calculated from the channel morphology survey). Flood peak discharges at the two study sites were compared to determine streamflow losses (due to percolation to groundwater) between the reaches, yielding a more accurate assessment of hydrologic conditions at the study sites.
Changes in sediment movement and storage can have a significant impact on the stability of an unconfined alluvial stream channel (Leopold and Wolman 1957). Future inventories will quantify how urbanization influences the movement of sediment through Rincon Creek and how changes in sediment movement will affect the channel's stability. Including the measurement of sediment movement in the monitoring effort will not only improve our understanding of how significant watershed disturbances, such as urbanization, affect sediment movement, but also how enhanced channel instability, and the concomitant destruction of streamside riparian ecosystems, can be reduced or even prevented.
For this study, the scour and fill technique (Gordon et al. 1992, Harrelson et al. 1994) was used to monitor sediment movement. Scour refers to the movement of bed material during a flood, and fill refers to sediment deposition that occurs as flood waters subside and fill in scoured areas. Recording the amount of scour and fill along various parts of a drainage system provides information describing how sediment is moving through the system.
To measure scour and fill, scour chains are installed in the channel bed. These are metal chains anchored onto metal plates and buried vertically in the channel bed (Fig. 4). When a flood scours away the bed material, the exposed chain falls flat, forming a bend. Subsequent filling reburies the chain. The amount of scour can then be determined by comparing the original length of chain buried to the length left below the bend, and the amount of fill determined by measuring the depth of sediment above the bend.
Two scour chains were installed along each of the three transects at Study Site C. The precise distance of each scour chain from transect lines, monuments and/or crest stage gauges (as well as approximate distance from the nearest bank) was measured and recorded so that they can be located in the future. Photographs of scour chain positions were also taken to aid in relocation. The initial elevation of the bed material at each site was obtained from the channel cross section data (see Channel Morphology Survey above), and the initial length of chain buried was recorded for each scour chain. These measurements allowed calculation of changes in bed elevation when the scour chains were monitored over time. Chains were excavated after peak flow events to measure any scour and fill, then straightened and reburied. If the new elevation of bed material was lower than the total length of the scour chain, the length of chain left exposed after reburial was also recorded (see Scour and Fill Data Collection Form in Appendix).
Groundwater is a significant controlling factor in the location and survival of phreatophytic vegetation and its associated wildlife populations (Dunne and Leopold 1978). Knowledge of the subsurface water level at a riparian site may be critical to interpretation of vegetation data, and can be a valuable monitoring tool (Myers 1989). Maps of groundwater changes can be prepared from measurement of water levels in wells (Todd 1964, Todd 1980). Water levels in aquifer systems that are in a state of equilibrium between long-term recharge and long-term natural discharge plus human withdrawals will exhibit normal seasonal fluctuations reflecting dry and wet periods of the year, with little change in elevation over long periods of time (Halpenny and Halpenny 1985). In aquifer systems that are in a state of disequilibrium, long-term monitoring will reveal significant changes in the groundwater levels.
Groundwater data were obtained from three abandoned private wells using measurement techniques based on those described in Todd (1980). Abandoned wells were chosen so that measurements would not be affected by cones of depression caused by pumping, but rather would reflect actual changes in elevation of the water table. Originally, four abandoned well sites were included in the study design. However, two of these wells could not be used because the depth of the well casing was consistently above the aquifer's potentiometric surface (i.e., the wells were often dry). An abandoned well south of Old Spanish Trail was therefore added to the study in July 1995. All three wells are located in the Rincon Valley in close proximity to the study sites (see Fig. 2 - pocket).
Water level was measured by lowering a weighted measuring tape into the well. Two of the wells were shallow enough that the length of submersion could be accurately read directly from the water line on the tape. For the third, much deeper well, the tape was covered with nontoxic, water-soluble paint so the length of submersion could be accurately read. The distance from the ground surface to the water surface was then calculated (see Data Collection Form for Groundwater Monitoring in Appendix). Groundwater elevations were adjusted with surface elevation differences between the well locations and the study sites.
Groundwater elevations were measured monthly by Rincon Institute staff and Rincon Valley residents who volunteered to participate in this project. Measurements were taken in the first week of each month. Volunteers were provided with the measuring tools and instructed on the proper procedure.
Plant communities provide most of the components of riparian habitat that are of critical importance to wildlife (Ohmart and Anderson 1986). The vegetation data chosen for study in this inventory are those that will enable future inventories to quantify changes in streamside plant communities. Vegetation response to urbanization in the Rincon Valley will be assessed by measuring changes in four parameters: diversity, density, trunk diameter and percent cover. These parameters were measured for live woody vegetation (trees and shrubs) and cacti. Future inventories will reveal how the number and distribution of these plant species change with space (between sites) and time (between inventories).
The methods used to locate sample plots and inventory riparian plant communities at each study site were based on procedures established by the U.S. Bureau of Land Management (Myers 1989) and the U.S. Forest Service (Platts et al. 1987). Vegetation data were collected by establishing sample plots extending from the transect lines used to collect channel morphology data. Long, rectangular plots were sampled in response to the characteristically riparian shape of the plant communities along Rincon Creek, which are elongated and parallel to the stream channel (Platts et al. 1987).
Distinct plant communities and their extent along each transect were identified based on vegetation structural classification parameters (diversity, size, and quantity of vegetation) described by Myers (1989) and Ohmart and Anderson (1988), and landscape features. In general, two sample plots were established randomly within each plant community encountered along a transect; in the case of extremely narrow communities, one plot per transect was sampled.
In order to represent the central tendency of each plant community and minimize influences from adjacent communities, sample plots were situated within homogeneous plant communities, and transitional areas near community borders (ecotones) were avoided (Platts et al. 1987). Five meters was chosen as the minimum distance that plots could be located from community borders; areas dissected by washes or roads were also avoided. Exact plot size and number of plots per transect varied in response to the shape of each plant community, the number of transects at the study site, and other unique site characteristics (see the site descriptions that follow).
At Study Site A, narrow, short plots (2 m x 20 m) were used in order to sample the three narrow communities present and avoid overlapping plots on the site's five transects. Due to a property line that prohibited access on the north bank of Rincon Creek, Plant Community 3 was only wide enough for one sample plot on four of the five transects (Fig. 5).
Study Site B is characterized by one large plant community dissected by several small washes. Due to the influence of these washes, density and diversity of plants varied within the community; fifteen plots (4 m x 30 m or 4 m x 40 m, depending on the proximity of washes and distance between transects) were therefore sampled to collect data representative of the overall community (Fig. 6). Areas heavily influenced by washes were not sampled.
At Study Site C, there is one plant community along the south bank and a second community along the north bank. Depending on community width at each transect line, one or two 2 m x 40 m plots were sampled in each community along each transect (Fig. 7).
Only one plant community is present along Rincon Creek at Study Site D. Three 2 m x 40 m plots were sampled along each transect, located randomly in the plant community between the multiple channels of this braided reach (Fig. 8).