2000 Progress Report: Alternative Urbanization Scenarios for an Agricultural Watershed: Design Criteria, Social Constraints, and Effects on Groundwater and Surface Water SystemsEPA Grant Number: R828010
Title: Alternative Urbanization Scenarios for an Agricultural Watershed: Design Criteria, Social Constraints, and Effects on Groundwater and Surface Water Systems
Investigators: Lathrop, Richard C. , Bahr, Jean M. , Bradbury, Kenneth R. , Greb, Steven R. , LaGro Jr., James A. , Nelsoni, Edward B. , Nowak, Peter , Potter, Kenneth W. , Zedler, Joy B.
Institution: University of Wisconsin Madison , Wisconsin Department of Natural Resources
EPA Project Officer: Packard, Benjamin H
Project Period: January 15, 2000 through January 14, 2003
Project Period Covered by this Report: January 15, 2000 through January 14, 2001
Project Amount: $886,105
RFA: Water and Watersheds (1999) RFA Text | Recipients Lists
Research Category: Water and Watersheds , Water
Objective:The objectives of this research project are to:
? Evaluate alternative management practices and patterns of urbanization by considering a range of urban development issues, including storm runoff, groundwater depletion, wastewater treatment, wetland degradation, thermal pollution, and eutrophication.
? Fill critical knowledge gaps and extend (or develop) analytical and modeling tools that will minimize the hydrologic and ecological impacts of urbanization.
? Construct comparable land use/water management scenarios for a test watershed (Pheasant Branch), including "low-impact development" designs, and evaluate their approximate economic costs, social/political acceptability, and hydrologic and ecological impacts.
? Examine urban impacts on wetlands, especially their biodiversity, and determine which native species can thrive in constructed urban bioretention wetlands or rain gardens.
? Evaluate farmer behaviors needed to reduce high soil phosphorus (P) concentrations in agricultural lands that are likely to be converted to urban development.
? Evaluate the social and institutional barriers to low-impact development, and provide guidance to local governments and citizen groups for improving the management and protection of critical aquatic resources in rapidly urbanizing landscapes.
Progress Summary:During the first year of funding, significant progress was made in all key areas of this multidisciplinary project. Engineering models have been modified to evaluate the impacts of rain gardens on infiltration. Spatially explicit soil samples were collected and analyzed for P throughout the agricultural portion of the Pheasant Branch watershed. An inventory of urban best management practices and their frequency of use has been made, and characteristics of past urban developments have been compiled from county records. Interviews of developers, urban planners, and design engineers have begun. These efforts are ongoing, and results are preliminary. Specific research findings of the hydrogeologic, wetlands, and thermal impacts subgroups of the project are summarized in more detail below.
Hydrogeologic Research. The focus of the hydrogeologic research during the first year of the project has been on field and modeling studies that will be used to address the following two important aspects of the project: optimal siting and operation of water supply wells, and evaluating groundwater quality and quantity tradeoffs between sewered and unsewered subdivisions. Although the groundwater flow model that is being constructed is for the Pheasant Branch watershed, general conclusions from this case study will be broadly applicable to a number of groundwater regions where multiple productive sedimentary bedrock aquifers are interlayered with confining geologic strata. There is a need for better tools with which to identify specific aquifers contributing to wetlands and springs and for a better understanding of how responses of these systems to urban impacts may vary as a function of the water source.
Field studies of the aquifer system in the Pheasant Branch watershed build
on, and complement, other research initiated in two nearby watersheds. Flow
meter logging and interval packer testing in wells of one of the watersheds
indicate that thin high permeability beds within the Tunnel City Formation are
the likely source of water to springs in that area. Geophysical logging and
drill cuttings show that this same formation occurs in the shallow bedrock near
the major springs of the Pheasant Branch watershed and the other watershed.
Further geophysical logging and packer testing will be conducted during the
spring of 2001 in these additional wells to determine if similar,
stratigraphically controlled preferential flow paths are likely sources of water
to all of the high volume springs in the area. Generic numerical and analytical
modeling results also indicate the feasibility of preferential flow through
thin, high permeability zones in
bedrock as a source for steady, high volume spring flow in this type of setting.
Wetland Vegetation Research. Research objectives for this subproject were to determine impacts of urbanization on downstream wetland plant communities and to design wetlands to retain urban stormwater and associated pollutants?a function requiring the wetland vegetation to tolerate flashy hydroperiods and high nutrient influxes. Twelve local wetland sites were surveyed twice in the summer of 2000. In addition, one experiment tested the tolerance of the native species to four hydroperiods, and another determined how the aggressive reed canary grass (Phalaris arundinacea, Pa) might invade and replace native species desired for urban rain gardens and wetland swales that would trap urban runoff.
The 12 wetlands were selected using indicators of hydrologic disturbance (3
sites with ~natural hydrology, 3 with increased surface water runoff, 3 with
decreased groundwater inputs, and 3 with both alterations). Each of the 12 sedge
meadows were sampled for species presence and cover in a stratified random
design. During July, 116 species were found with a mean of 10 species per plot
(range of 1 to >20). Sites with relatively natural hydrology were the most
species-rich; those with both ground and surface water alterations were
species-poor. Vegetation patterns were not distinguishable for surface vs.
groundwater alteration. Preliminary conclusions are that southern Wisconsin
sedge meadows retain moderate species diversity. However, diversity plummets
where hydrologic alteration favors invasive species such as Pa, Phragmites, and
cattail (Typha). Several of the native sedge meadow species coexist with these
invasive species and show promise of utility in urban wetland
Seventeen common wetland plants (15 native and 2 invasive spp.) were evaluated under four hydrologic regimes: (1) plants constantly watered from the bottom; (2) six episodes of flooding for 4 days followed by watering from the bottom for 4 days; (3) flooding for 4 days followed by 4 days without watering; and (4) constantly flooded. All four treatments received the same high levels of nutrients typical of surface runoff. As hypothesized, taxa typical of fens tended to be the most sensitive to flooding. Such species should be avoided in planting urban wetlands. Also as expected, widespread graminoids and forbs were intermediate in sensitivity. Most of these have good potential for use in urban wetlands. An additional test of two Spartina populations found significant biomass differences for three of the four hydroperiods; one population appeared less sensitive to long-term flooding than the other. It may be possible to exploit such intraspecific variation in flood tolerance to increase the chances for successful establishment of native species in urban wetlands. The two potentially invasive species, Pa and cattail, were consistently among the most productive and least sensitive taxa, despite biomass declines in the "4 High/4 Dry" treatment. Results suggest that high tolerance to flashy hydroperiods contributes to their invasiveness in wetlands with urban runoff.
The ability of Pa to invade established wetlands that differ in canopy cover and nutrient inflows was studied in both the field and in microcosm experiments. Dense plant canopies limit the establishment of Pa rhizome fragments. Thus, planting native wetland species that rapidly form dense canopies can decrease the Pa invisibility in urban wetlands. Another finding was that nutrients facilitate the growth of established Pa. Hence, reducing nutrient loading to urban wetlands may slow the vegetative expansion of established clones. Finally, the resource subsidy of established Pa clones facilitates vegetative expansion into heavily shaded areas. Because dense canopies are not a barrier to Pa expansion, Pa establishment needs to be detected early and removed to maintain native vegetation.
Research on Thermal Impacts of Urban BMPs. Increased water temperature is an often overlooked water quality concern for urban best management practices (BMPs). This subproject examined three urban BMPs (0.43-ha wet detention pond, 0.10-ha bioengineered wetland, 26-m long grass swale) and quantified their impact on the thermal regime of runoff water. Water temperature and flow at the inlet and outlet of each BMP were monitored during 4-5 summer runoff events. Using these data, heat budgets were developed for each event, with heat change calculated relative to rainfall (air) temperature.
Of the three BMPs, the wet pond contributed the greatest amount of additional heat to the water, resulting in an average volume-weighted heat increase of 20 percent. This heat was from previously stored water, which was displaced during a subsequent storm. The wetland complex increased the heat output of runoff water by an average of 10 percent. The smaller heat increase of the wetland was due to its smaller water storage capacity with less heat retained than in the pond. In contrast, runoff water passing over the grass swale actually lost heat (- 43 percent). This loss was a result of water lost through infiltration and the complement of heat that it contained.
Urban Development Research. An inventory of stormwater management literature and public policies implemented in communities across the United States was compiled. In preparation for designing plausible development scenarios, a systematic analysis of the residential subdivision development that occurred in Dane County during the 1990s was conducted. Data about recent development practices will be used in constructing alternative development scenarios. Several attributes are being recorded for each selected subdivision, including building arrangement (e.g., dispersed, clustered); dwelling unit density; street design (e.g., pavement width, edge treatment, configuration); open space patterns (e.g., dispersed, contiguous); landscape context (e.g., adjacent land uses and covers); and stormwater management (e.g., one or more BMPs at both the lot and subdivision scale). These physical attributes will be among the independent variables (or treatments) for the models of development impacts on hydrology and biodiversity.
Future Activities:The main focus of the research in 2001 will be on developing the information, tools, and models to evaluate alternative management practices and modes of urban development. Field studies will be conducted to test hypotheses on the stratigraphic controls on spring flow. The results of that work will be used to develop the groundwater flow and solute transport models that will be used to assess the impacts of urbanization on spring flow and groundwater quality. An experimental rain garden will be constructed and instrumented to demonstrate the practice and test our numerical rain garden model. Scenarios for urban development will be designed that will allow multiple-scale modeling of their hydrological and ecological impacts. Finally, work will begin on multiscale hydrologic modeling of alternative management practices and modes of urban development.
Research also will be conducted to further determine the relationships between wetland biodiversity and hydrologic alterations. The soil P data in agricultural areas will be combined with biophysical characteristics of the watershed as well as farmer fertilizer practices to determine why soil P hotspots may occur in certain landscape areas. In addition, we will continue to investigate possible barriers to the adoption of low-impact development modes and practices. To this end, we will continue interviews of the various interest groups involved in urban development. We will facilitate these interviews through the use of computer visualizations of development modes and practices.