2001 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, 2001 through January 14, 2002
Project Amount: $886,105
RFA: Water and Watersheds (1999) RFA Text | Recipients Lists
Research Category: Water and Watersheds , Water
Objective:The objectives of the project are to elucidate the mechanisms and further develop the models used to assess hydrological impacts in relation to various conditions and scenarios, while also evaluating and assessing groundwater relationships.
Hydrogeologic Research. In Year 2, we further elucidated the mechanisms controlling spring flow and groundwater discharge to wetlands in the region. An understanding of these controls is essential to the development of numerical models that will be used in the process of evaluating the hydrologic impacts of various urbanization scenarios and to address two major objectives of this project: (1) optimal siting and operation of municipal and other high-capacity wells; and (2) evaluating groundwater quality and quantity tradeoffs between sewered and unsewered subdivisions. Extensive testing of a deep well borehole drilled near the major springs in our case study watershed (Pheasant Branch) provided stratigraphic information that confirmed the presence of a regional aquitard (shale) separating the upper and lower bedrock aquifers. The effects of pumping by nearby municipal and other high-capacity wells on water levels in the upper and lower bedrock aquifers were evaluated by examining continuous water-level records from two zones of the test well separated using an inflatable packer. Comparison of the water level data to records of precipitation and pumping rates for nearby wells revealed that pumping causes frequent cycling of water levels in the lower aquifer, while the upper aquifer has relatively steady water levels that respond primarily to precipitation. These results illustrate the effectiveness of the regional aquitard in isolating the lower bedrock aquifer. The results also confirm the hypothesis that steady spring flow rates are maintained by water discharging from the shallow bedrock. Thus, a decrease in infiltration due to urbanization would directly reduce spring flow rates entering the wetland.
Two other components of hydrogeologic research were initiated in Year 2. A field study designed to characterize water levels and hydrogeochemistry along a transect through a relatively pristine wetland is providing valuable information to constrain mesocosm experiments and interpretation of field data collected at reference sites by wetland ecologists working on this grant. A separate grant from the WI DNR provides funding for field instrumentation at a proposed subdivision in the eastern part of the county. Analysis of water quality data collected at this site will contribute to the evaluation of urbanization effects on water quality, and of trade-offs between sewered and unsewered subdivisions.
Wetland Vegetation Research. The wetland vegetation work seeks to identify urbanization impacts in wetlands and native species that can be grown in bioretention areas designed to reduce runoff and increase infiltration. In summer 2000, we sampled 12 wetlands and identified patterns of vegetation that related to hydrological disturbances, including sedimentation. Wetlands with the most altered hydrology tended to be dominated by invasive species. In summer 2001, we sought to make more direct links between hydrology and vegetation by assessing both along elevation/disturbance gradients in three wetlands, each of which has areas of natural vegetation grading into areas dominated by invasive plants.
In our outdoor mesocosm experiments, we identified plant species that are likely to grow well in bioretention areas, including rain gardens. The tolerance of 17 taxa to 4 hydroperiods were tested by growing the plants in pots with nutrient-rich soil and controlled water levels. Invasive species (cattails and Reed Canarygrass) grew best under all conditions, indicating that they are a serious threat to native-species plantings. However, four native species show promise for bioretention areas, while other species, including those from fens, were least suitable due to slow growth and inability to tolerate flooding. Our results suggest that rain gardens can be planted with the following native plants: Carex stricta, Calamagrostis canadensis, Spartina pectinata, and Eupatorium perfoliatium, based on their biomass production and a new index of flooding sensitivity that we are developing. In addition, field and greenhouse experiments further show that native-species plantings should provide dense canopies so that heavy shade will reduce invasion by Reed Canarygrass. A fact sheet about Reed Canarygrass has been drafted for publication and dissemination by the Wisconsin Department of Transportation to staff and others who restore and manage wetlands.
Infiltration Practices Research. Progress continued on development of a physically based numerical model of the performance of rain gardens. Progress also continued on the development of simpler operational models of rain gardens and other infiltration practices for use in routine design. At a new nature center in the Madison area, an experimental rain garden was constructed in 2001, by project personnel to demonstrate the capability to infiltrate roof runoff, while providing data for model validation. The rain garden is instrumented to provide measurements of rainfall, roof runoff, overflow discharge, percolation, and soil moisture at multiple depths.
Transitional Agricultural Lands Research. Post-harvest soil sampling (5 cm depth) in fall 2000, provided the basis for mapping phosphorus (P) levels across a 1,220 ha (3,028 ac) study region, which included 10 animal feeding operations (AFOs), ranging in size from 92 to 1,600 animal units. The sampling effort was accompanied by on-farm interviews. Our research revealed trends related to P management that have implications for agricultural watersheds undergoing urbanization. First, high soil P levels greater than 200 ppm (as Bray P1) exist at the farm, field, and subfield scales, covering approximately 15 percent of the study area. These high soil P areas developed as a result of a legacy of manure additions, aided by runoff generation and sediment transport, establishing the potential for P migration from agricultural fields. Current policy goals, such as the Unified National Strategy for Animal Feeding Operations, focus on reducing high P levels through nutrient management planning in an effort to prevent large deliveries of P to aquatic ecosystems.
We have learned, however, that the process of soil P build-up in urbanizing watersheds is markedly different than in exclusively agricultural watersheds. In urbanizing watersheds, many AFOs, especially large ones, rely heavily on rented land for crop production and manure distribution. Land rental is common because most producers and farmers are aware of real estate prices, and are unwilling to sell land entirely. As producers rely more heavily on rented land, their "land bases" become fluid and uncertain. There is a trend in Wisconsin, as in other areas of the country, for dairy AFOs to expand herd sizes using the confinement model of dairying. Environmental problems arise when land that is needed for manure distribution becomes lost to development, while the number of animal units remains the same. Development pressures "squeeze" animals onto fewer acres for a period of time, while producers seek out more land elsewhere. Some AFOs are able to acquire land in close proximity to the animal housing centers, while other producers are left to find land that is more distant and often external to the watershed.
Urban Development Research. The past year's work focused on two related activities: (1) a field survey of about 100 sampled subdivisions platted between 1990 and 2000 in the cities, villages, and towns of Dane County, Wisconsin; and (2) an inventory of subdivision ordinances for all 60 minor civil divisions in the county. Data collected at each subdivision included qualitative and quantitative measures of the development's context in the landscape (e.g., adjacent land uses) and its physical design. Several design attributes were measured, such as the widths of streets and cul-de-sacs, and the methods of stormwater management. Digital photographs also were taken of each subdivision's key attributes. All of the cities (9), villages (19), and towns (34) in Dane County were asked for a copy of their land subdivision or land division ordinances. We obtained ordinances from all local units of government except for 17 towns and 3 villages. Towns without ordinances either used the county ordinance (7), or did not allow subdivisions (10), some due to the existence of exclusive agricultural zoning in the town. 3 villages did not have ordinances due to lack of vacant properties within their jurisdictions.
A content analysis of each subdivision ordinance is yielding information about the policy influences on various subdivision attributes including: site layout, street design, lot sizes and configurations, street trees and open space, and stormwater management. The completed inventory will document the prevalence of particular regulatory practices in the county and the relationships between subdivision ordinances and the built environment (specifically, residential subdivisions). This inventory is ongoing, but preliminary findings reveal inconsistencies within some individual ordinances, as well as considerable differences among ordinances. More important, the ordinances are evidence of existing public policy barriers to low-impact subdivision development.
Sociological Research. We conducted in-depth personal interviews with a wide range of individuals (e.g., municipal officials, regional planners, builders, developers, engineers, and environmental consultants) instrumental in the adoption of alternative stormwater management practices. These interviews disclose that the adoption of even a single, simple practice, such as a rain garden, is a potentially complex event. A large number of actors and considerations are important, including cost; the physical, institutional, and legal environments; and the understanding of various key actors (engineers, builders, developers). Interestingly, home owners and renters are of scant importance in driving the decision to install these practices. It appears that decisions on these matters are made early in the development phase and that owners/tenants have little input or impact.
An additional finding of our sociological research is a key barrier to the adoption of infiltration practices, knowledge about the practices, and their effectiveness under different conditions. Conventional stormwater management practices are well understood; their alternatives are not. Builders, developers, planners, regulators, and municipal officials need to know how these practices can be installed, how well they function in different settings, and what they cost to install and maintain. Additional research and documentation of the practices can overcome this barrier. Other barriers may be more intractable. Not every setting is suitable for such practices. Steep slopes, impermeable soils, and shallow aquifers may be insuperable barriers to adoption of infiltration practices. Likewise, municipal officials and ordinances may not provide a welcoming environment. Ordinances, for example, call for standard practices (curbs, gutters, street widths) and embody the interests and views of various institutional players (e.g., fire department and snow removal personnel). Builders and developers have scant experience with the design and construction of these practices.
In Year 3 of the project, we will be completing our wetland and hydrogeologic field research. The main thrust will be to further refine our multi-scale modeling work including linking infiltration practices with spring flows rates. Urbanization scenarios using standard and low-impact development designs for infiltrating water will be tested using the hydrogeologic models to determine their relative impact on groundwater flow rates in our test watershed. Work will begin on presenting these alternative development designs to various institutional and housing development players using computer visualization techniques. Strategies will be prepared for overcoming the barriers to adopting low-impact development.