The project described in this handbook is using a significant reach of Rincon Creek southeast of Tucson, Arizona as a living laboratory to establish the basis for evaluating the consequences of development on riparian habitats. The 12-km reach being studied currently passes through low-density housing, abandoned agricultural land, and mesquite bosques. However, during the next 10 years, the Rocking K Ranch, through which Rincon Creek passes, will be extensively developed and the degraded reach of the creek that lies within the ranch will be restored once development begins.
Since the initial, baseline inventory of Rincon Creek's riparian habitat was completed prior to major development, comparing the results of future inventories to the baseline database will provide a unique opportunity to assess in detail the impacts of development on riparian habitat. Such an assessment will contribute significantly to the understanding of how development alters riparian habitat processes and how healthy riparian habitats can be protected in an urbanizing environment. In addition, the restoration of the reach of Rincon Creek that passes through the Rocking K Ranch will provide an opportunity to assess the effectiveness of riparian restoration in an urbanizing landscape.
A critical aspect of this project is that it combines an assessment of riparian plant communities with an evaluation of groundwater, streamflow, sediment movement and channel morphology, all important factors in determining the overall health of a riparian ecosystem. Degraded riparian ecosystems are often characterized by reduced plant community density, diversity, and volume, and are often associated with altered hydrologic characteristics and unstable alluvial channels. Determining how these ecosystem characteristics are influenced by human activities (e.g., changes in land use such as development) will provide insight into not only how these important ecosystems become degraded, but also how to most effectively improve the condition of degraded riparian habitat and prevent the degradation of healthy riparian areas.
Rincon Creek drains a large portion of the southwestern side of the Rincon Mountains east of Tucson, Arizona, and flows almost due west through the Rincon Valley to its confluence with Pantano Wash (see Fig. 1 - pocket). The Rincon Creek watershed is described in detail in section I.C. below. This project focuses on the lower reaches of Rincon Creek, downstream from the pediment after the creek has descended from the foot of the Rincon Mountains into the Rincon Valley. Here, channel gradients are shallow and the channel is unconfined.
Along these lower reaches, Rincon Creek flows through a variety of riparian ecosystems. Moving along Rincon Creek in a downstream direction, you will encounter plant communities dominated by such overstory species as Fremont cottonwood (Populus fremontii), Goodding willow (Salix gooddingii), Arizona sycamore (Platanus wrightii), and such understory species as seep willow (Baccharis glutinosa). Further downstream, riparian plant communities change to an overstory dominated by mesquite (Prosopis velutina) and netleaf hackberry (Celtis laevigata), and understories dominated by catclaw (Acacia greggii) and burrobush (Hymenoclea monogyra).
Human impacts are not obvious until Rincon Creek passes through the Rocking K Ranch. In this area, abandoned agricultural fields dominated by such colonizing species as desert broom (Baccharis sarothroides), burrobush (Hymenoclea monogyra), ragweed (Ambrosia ambrosoides), burroweed (Isocoma tenuisecta), and Russian-thistle (Salsola kali) are common along the floodplain.
Sixty years ago streamflow was almost perennial along this reach of Rincon Creek, and the floodplain was dominated by Arizona walnut (Juglans major). Interviews with long-time Rincon Valley residents tell of numerous beavers that made their homes along this reach (Hodge 1994, pers. comm.). Since that time, the riparian ecosystems, hydrology, and channel morphology characteristics of the Rocking K reach have been altered significantly. Today the reach flows only after heavy rains. The walnuts were removed to make way for agriculture and grazing; and groundwater pumping, channelization and the construction of retention basins along tributaries have changed the reach's hydrology and channel morphology by influencing sediment aggradation rates (Lane, pers. comm., 1994). Native, riparian ecosystems are not found again until Rincon Creek leaves the Rocking K Ranch and enters Thunderhead Ranch. Here, ecosystems are once again dominated by mesquite and netleaf hackberry.
This project inventoried riparian habitat along the reach of Rincon Creek that begins 8 km upstream from the proposed Rocking K development and ends 1 km downstream from the proposed development.
During the next 10 years, the land bordering Rincon Creek where it passes through the Rocking K Ranch will experience extensive urbanization. The Rocking K specific plan proposes a mixed-use, resort-oriented community that will include a variety of residential densities and areas, resorts and golf courses, retail space, research and development, and a resort village center with office, retail and higher density residential development.
A condition of the Rocking K Specific Plan calls for the restoration of the Rincon Creek reach that passes through the Rocking K. The purpose of this restoration project is to reestablish a riparian environment along Rincon Creek by revegetating the heavily disturbed lands and reforming the Rincon Creek channel. As outlined in the Rocking K Specific Plan, the developer will work with Pima County Department of Flood Control and the Rincon Institute to develop strategies that will improve the overall ecological condition of this reach of Rincon Creek. The preliminary restoration plan calls for the re-establishment of a riparian woodland that is dominated by large, native riparian trees, including mesquite (Prosopis velutina), Arizona walnut (Juglans major), Arizona sycamore (Platanus wrightii), and Fremont cottonwood (Populus fremontii).
This handbook describes the methods and results of the initial Rincon Creek riparian habitat inventory. Specifically, permanent transects were established across the Rincon Creek channel for measuring channel morphology and plant community characteristics; groundwater monitoring was initiated at several pre-existing wells; crest stage gauges and scour chains were installed for monitoring streamflow and sediment changes in the channel; photo points were established to document current conditions at each study site; and a Geographical Information System database containing all data collected by this baseline inventory was created.
The handbook has three principal objectives:
Performing this inventory prior to the onset of construction offers a rare opportunity to assess how urbanization influences riparian habitat conditions. The information contained in this handbook provides the basis for a long-term riparian habitat monitoring program that will evaluate the impacts of urbanization on Rincon Creek's riparian habitats. Subsequent inventories will be performed every 2 to 5 years, depending on funding. Comparing the results of future inventories to this baseline inventory will allow assessment of how urbanization affects riparian plant communities and the abiotic processes that are so important in determining their health (channel morphology, streamflow and sediment movement, and groundwater).
A better understanding of the impacts of development on riparian habitats will also improve the ability of resource managers and land use planners to mitigate those impacts before the habitat becomes degraded and wildlife resources adversely affected. For example, evaluating the effects of development on sediment movement and channel stability will improve our understanding of how to alter future construction and development plans to lessen their impact on riparian areas.
Data collected in future inventories will be added to the Geographical Information System (GIS) database in order to create a dynamic model which will allow prediction of habitat changes under different conditions. For example, once the various data (ground water, hydrologic, streamside vegetation, channel morphology) from a second inventory are incorporated in the GIS database, land managers will be able to predict riparian habitat changes given a change in ground water conditions.
The upcoming restoration of the reach of Rincon Creek that passes through the Rocking K Ranch provides another unique opportunity: to assess in detail the effectiveness of specific techniques for restoring a damaged riparian habitat in an urbanizing setting. Future inventories of the Rincon Creek reach that passes through the Rocking K Ranch will be modified so that the effectiveness of restoration (e.g., the survival of planted vegetation, channel stability, wildlife use, etc.) can be evaluated in detail. Since the monitoring effort also includes an evaluation of Rincon Creek's hydrologic characteristics, future inventories will also allow an assessment of how riparian restoration influences streamflow characteristics and transmission losses.
The strategies and protocols used to conduct the inventory of riparian habitat along Rincon Creek are described in this handbook so that it can be used as a resource not only in future monitoring efforts at Rincon Creek but also for application at other riparian sites in the desert Southwest.