Build Out Analysis

In addition to completing a natural systems evaluation a visual assessment was completed, as well as a public infrastructure evaluation. The study also conducted a build out analysis, an analysis which assists in determining where future development can take place. The study analyzed the type and intensity of development based on current zoning and existing master plans. The result of the build out analysis was an estimate of the number of potential dwelling units and population for the Mitchell Creek Watershed (Becker and Raeder, 1996).

The Mitchell Creek watershed was divided into cells, 500' x 500', making it amenable to raster GIS functions. Each cell was coded with the following information: a cell identification number, acreage, zoning classification, master plan classification, percent of cell with slopes between 12-18%, percent of cell with slopes greater than 18%, percent of cell having wetlands, percent of cell with an aquifer recharge area present, percent of cell with a stream tributary, percent of cell that has existing development, visual classification, and sanitary sewer area.

The zoning ordinances for the four municipalities were consolidated in order to determine the current development condition of the watershed. Zoning class was cross tabulated with wetlands and also with aquifer recharge in order to gain a better understanding of the watershed character. Similarly, the master plans for the four municipalities were combined to determine a watershed wide land use classification scheme. The master plan classification was cross tabulated with the zoning classification and revealed that approximately 57% of the land was zoned consistently with the master plan.

Through the use of GIS and data, build out analysis can be completed efficiently.Buildable acreage was determined by:

Gross Acreage of Cell - 82% of total percent of cell with slope over 18%*- % cell classified as wetland - % cell classified as stream/tributary - % cell that is already developed = Net Acreage

Net Acreage - 30% for interior infrastructure, circulation, easements and site development = Buildable Acreage

Buildable Acreage divided by Zoning Regulation Dwelling Unit per Acre = Potential Households

Potential Household x Average Household Size for Watershed (2.44 persons/household) = Potential Population

* To address development limitations posed by topography, existing conditions were examined by cross tabulating cells with slopes greater than 18% with existing development. This analysis indicated that in areas with slopes greater than 18%, approximately 18% of the land area had been developed in some form.

What are the ramifications of perceiving the watershed as an area that should maximize its buildable potential versus determining the minimal development needs?

A limitation of this methodology introduces the notion of scale. The methodology does not accommodate for parcels where a property boundary extends over several cells. For example, if one dwelling unit per acre is allowed, the grid size is smaller than an acre, and the parcel covers more than one grid, a build out analysis will erroneously indicate that a new dwelling can be established in each of the grids. Thus, one cell could be classified as fully developed while the other cells would be defined as buildable. All of the cells, however, are actually not available for future development.