Site Attributes - Physical Attributes PDF

APLANN01: SITE ATTRIBUTES – Physical Attributes Ar. Diane A. Jose, MBA, PIA, UAP  SITE SELECTION PROCESS Recap… OVERVIEW Site Inventory OVERVIEW The site inventory is an essential step in understanding the character of the site and the physical, biological, and cultural linkages between the...

APLANN01: SITE ATTRIBUTES – Physical Attributes Ar. Diane A. Jose, MBA, PIA, UAP  SITE SELECTION PROCESS Recap… OVERVIEW Site Inventory OVERVIEW The site inventory is an essential step in understanding the character of the site and the physical, biological, and cultural linkages between the site and the surrounding landscape. Inventory – make or include in an itemized record or report. OVERVIEW Decisions to develop or restore a parcel of land require an understanding of the site as well as the surrounding landscape. Because site planning and design involve decisions about future uses of land, an understanding of human behaviour, attitudes, and preferences is also necessary. Yet the site inventory is a focused process of collecting and mapping essential attribute data. SUSTAINABILITY IS… Sustainable design, sustainable development, design with nature, environmentally sensitive design, holistic resource management—regardless of what it’s called, ”sustainability,’’ the capability of natural (context or setting) and cultural (human) systems being continued overtime, is key. —U.S. National Park Service THREE (3) SITE ATTRIBUTES Site Inventory  THREE (3) SITE ATTRIBUTES 1. Physical Attributes 2. Biological Attributes 3. Cultural Attributes PHYSICAL ATTRIBUTES Site Inventory  1. PHYSICAL ATTRIBUTES Sub-Category Attribute Soils Bearing Capacity Stability Erodability Fertility Topography Elevation Slope Hydrology Surface Drainage Aquifer recharge areas Depth to seasonal water table Geology Seismic hazards Depth to bedrock Climate winds Solar access Site Data that may be conveyed on a Topographic Survey 1.1 PARCEL SIZE AND SHAPE 1. Physical Attributes 1.1 Parcel Size and Shape Land development—and redevelopment—occur over a range of site scales. For example: Many single-use commercial projects require relatively small sites of less than one acre (0.4 hectare). In contrast, large-scale residential and mixed-use developments may require sites of 10 or more acres (4.05 hectares). Sometimes, two or more contiguous parcels of land are combined to create one larger parcel under a single ownership. 1.1 Parcel Size and Shape Parcel size or area is an inherent constraint on a site’s development potential. If all other factors are equal, larger sites can accommodate more extensive and more diverse development than smaller sites. Local zoning regulations, for example, may limit site development by restricting building height, building site coverage, and housing density. 1.1 Parcel Size and Shape The shape of the site can have an impact on reducing development potential and design flexibility. This is especially true on smaller sites and on narrow, linear sites that have a higher edge-to-interior ratio than properties that are more compact in shape 1.1 Parcel Size and Shape The greater proportion of ‘‘edge’’ increases the site’s exposure to the surrounding landscape. If the site is adjacent to a busy highway or other nuisance land use, for example, a linear or small site will substantially limit the site planner’s ability to buffer the undesirable noises and visual impacts. Edge - boundaries and breaks in continuity 1.1 Parcel Size and Shape However, if the site is adjacent to a natural amenity, a parcel with a relatively high edge-to-interior ratio will benefit from this proximity, particularly if the amenity is likely to persist well into the near future. IDEALLY… Physical Attributes SOME SAD REALITIES… Physical Attributes 1.1 Parcel Size and Shape In combination, the size and shape of a site can significantly affect its suitability for potential development. Municipal zoning regulations, for example, may impose building ‘‘setbacks’’ from front, side, and back property boundaries. These or other development restrictions can occupy a relatively large percentage of a linear site’s total area and potentially render the site infeasible for development from a financial perspective. Source: IRR NBC 1096 1.1 Parcel Size and Shape In addition to onsite constraints, the immediate surroundings of potential sites are also important considerations in the site inventory. Context is particularly important when evaluating small or linear sites for uses that are potentially incompatible with the surrounding land uses. 1.2 TOPOGRAPHY 1. Physical Attributes 1.2 Topography TOPOGRAPHY is the art or practice of graphic delineation in detail usually on maps or charts of natural and man-made features of a place or region especially in a way to show their relative positions and elevations. Three (3) fundamental landform components: Elevation, Slope, and Aspect 1.2.1 Topography - Elevation ELEVATION the height of a place. Site elevations, for example, affect both drainage patterns and visibility. Variation of elevation on a site and the surrounding landscape determines the size and spatial configuration of local view sheds. Visible areas may encompass portions of the site, or the entire site, and they may extend into the surrounding landscape. 1.2.1 Topography - ELEVATION: Mapping Elevation data are typically portrayed as contour lines on topographic maps. For site planning purposes, however, an effective way to visualize topographic relief is to create a chloropleth map of elevation. The map should have relatively few (five to nine) classes of elevation. The range of existing elevations on and adjacent to a site determines the range of each elevation class. *Chloropleth map is a thematic map in which areas are shaded or patterned in proportion to the measurement of the statistical variable being displayed on the map – e.g. elevation Example of Chloropleth Map 1.2.1 Topography - ELEVATION: Mapping For example, highest elevation = 1327 meters above a local benchmark lowest elevation = 832 meters with 6 classes Find the Range: 1327 – 832 = 495 meters 495 / 6 classes = 82.5 meters or 100 meters Each ‘‘layer’’ is then shaded or colored—typically with a spectrum ranging from cool colors (low elevations) to warm colors (high elevations)—to enhance the map’s effectiveness 1.2.2 Topography - SLOPE SLOPE (also called GRADIENT) of a straight line shows how steep a straight line is. Slopes are the result of constructional processes (for example, deposition) and destructional processes (for example, erosion) acting on geologic structures (Bloom, 1978). Moreover, the slopes of undeveloped sites reflect the local area’s surficial geology. 1.2.2 Topography - SLOPE A site’s suitability for roads, walkways, buildings, and other structures is, in part, a function of the existing slopes on the site. In Hong Kong and San Francisco, for example, development frequently occurs on sites with steep slopes. But these cities have relatively warm climates. In locations with freezing winter temperatures, steep slopes are a significant safety concern when designing vehicle and pedestrian circulation systems. Gradients must be relatively low to prevent slipping on icy surfaces. 1.2.2 Topography – SLOPE: Mapping Slope gradients can be computed with most (Geographic Information Systems) GIS and CAD software and easily mapped. 1.2.2 Topography – SLOPE: Mapping Different colors are typically used to identify different slope classes. The range of each mapped slope class depends on the intended uses of the site and the specific site and contextual conditions, including soil characteristics, vegetative cover, and applicable regulatory requirements. 1.2.2 Topography – SLOPE: Mapping For example, to prevent significant environmental and aesthetic impacts from new development, municipalities or other regulatory agencies may prohibit construction on very steep slopes (for example, greater than 25 percent) and require special design and construction methods on moderate to steep slopes (for example, 8 to 15 percent or 15 to 25 percent). 1.2.2 Topography – SLOPE: Mapping Conversely, sites that are essentially flat (for example, less than 1 percent slope) may be poorly drained. Each of these different slope conditions warrants mapping, because these locations must be considered in the planning of the site. 1.2.3 Topography – ASPECT ASPECT is a slope’s orientation, or simply the direction that the slope faces. Aspect is typically identified, therefore, by compass direction (for example, north or northeast). Variation in slope and aspect influence the amount of solar radiation received by the site on a daily and seasonal basis. 1.2.3 Topography – ASPECT For example, in the Northern Hemisphere, north-facing, ten degree slopes will receive less solar radiation than south- facing slopes of the same gradient. 1.2.3 Topography – ASPECT In the winter, the sun’s highest point above the horizon is an acute angle. The north-facing slopes, when exposed to direct sunlight, receive less solar radiation per unit surface area than do the south-facing slopes. Because the slope faces away from the sun, the solar radiation striking a north-facing slope hits the surface at a shallow, or acute, angle. 1.2.3 Topography – ASPECT 1.2.3 Topography – ASPECT As with other physical attributes, the importance of a slope’s aspect depends, partly, on the proposed uses of the site. At higher northern latitudes, for example, south-facing slopes are better suited for siting buildings that will incorporate active and/or passive solar heating. A project that involves siting downhill skiing slopes will certainly consider slope, elevation, and aspect. Conversely, a north-facing slope may be better suited for ski trail development in areas with relatively mild winters, to limit the melting of snow from direct solar radiation. 1.2.3 Topography – ASPECT: Mapping Typically, aspect is classified using eight (8) categories: north, northeast, east, southeast, south, southwest, west, and northwest. These are portrayed graphically by either shading or color. Aspect influences microclimate by affecting the level of solar radiation that strikes the site. *Therefore, more shaded northern slopes (in the Northern Hemisphere) are rendered with cooler colors or heavier hatching than are the other slopes with greater solar exposure. 1.3 GEOLOGY 1. Physical Attributes 1.3 Geology (Landform) GEOLOGY is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which they change. Elevation and slope are good examples of quantitatively expressed landform attributes. Landform classification describes significant physiographic features of terrestrial, riparian, and aquatic environments. Landform classification is useful in site or regional inventories and analyses, particularly for characterizing difficult-to- quantify attributes like scenic beauty, sense of place, and landscape character. 1.3 Geology (Landform) Landforms, in conjunction with vegetation, define view sheds, or visibility on a site, and can create visual interest. Landforms also influence microclimate, storm water runoff and infiltration, and the distribution of plant and animal species. 1.3 Geology (Landform) Surficial geology is concerned with the structure, composition, and stability of the materials beneath and—in some locations—at the earth’s surface. In some landscapes, bedrock is buried many yards or meters below the ground surface. 1.3 Geology (Landform) Bedrock geology has a persistent effect on landforms, due to the different rates of weathering that occurs on the soil parent materials. Soil formation, soil erosion, and soil deposition are natural processes that involve rock fragmentation and weathering. Weathering occurs unevenly because of variations in the bedrock’s chemical composition and structure. 1.3 Geology (Landform) An important attribute of surficial geology is the depth-to- bedrock. Example: If excavation is planned for building foundations or for other site structures, the depth to bedrock should be investigated. If excavation is planned for a site with shallow bedrock or glacial eratics (boulders), blasting or other special methods of removal may be necessary. The cost of excavating a cubic yard or meter of rock is many times greater than the cost of excavating the same volume of soil. Consequently, these difficult subsurface conditions can significantly increase the costs of construction. 1.3 Geology: Mapping A geologic map shows the age and distribution of rock layers and other geologic materials. These attributes influence a site’s suitability for excavation and grading, wastewater disposal, groundwater supply, pond construction, and other common land development objectives (Way, 1978). Geologic maps also show locations that are susceptible to earthquakes, landslides, and other hazards. 1.3 Geology: Mapping Volcanic activity and earthquakes are relatively common events in some parts of the world. These geological disturbances are potentially devastating hazards that must be considered when planning new development in these areas. In some landscapes, especially those impacted by deforestation, landslides are also common. The locations of potential natural hazards can be documented in the site inventory Themes for Geological Maps 1.4 HYDROLOGY 1. Physical Attributes 1.4 Hydrology HYDROLOGY is the study of the movement, distribution, and quality of water on Earth and other planets, including the hydrologic cycle, water resources and environmental watershed sustainability HYDROLOGIC CYCLE 1.4 Hydrology Water circulates in the environment through precipitation, overland flow, infiltration, storage, and evapotranspiration. Groundwater moves by capillary action through the porous spaces between unconsolidated sand, gravel, and rock, and between the fractures and faults in the underlying bedrock. The upper surface of the saturated area, the water table, generally mirrors the surface terrain. In landscapes where groundwater is the source of local or municipal wells, groundwater pumping can have substantial impacts on the depth of the water table. 1.4 Hydrology Topographic relief creates drainage patterns, which, in turn, influence vegetation associations and distributions. The spatial correlation between vegetation associations and site drainage patterns is particularly strong in arid and semiarid landscapes where water is often the primary limiting factor on plant growth and distribution. 1.4 Hydrology Although the groundwater–vegetation linkage is more subtle in less arid environments, the continuous— or seasonal saturation of soils creates suitable conditions for wetland vegetation. In coastal environments, brackish or saline surface and groundwater result in the development of salt marshes and other distinct wetland communities. 1.4 Hydrology Without mitigation, urban development can have significant impacts on local and regional hydrology, including the following (United States Environmental Protection Agency, 1993): 1. Increased volumes and rates of runoff discharges 2. Reduced time needed for runoff to reach surface waters 3. Increased frequency and severity of flooding 4. Reduced stream flow during prolonged periods of dry weather 1.4 Hydrology Land development usually involves the construction of buildings and paved surfaces that are impervious or nearly impervious. Any site-disturbing activities can increase the risks of flooding, erosion, and other ecological impacts to properties ‘‘downstream.’’ For this reason, storm water management is an increasingly regulated component of the land development process. 1.4 Hydrology Land use changes may also negatively impact water quality. Contamination may result, for example, from erosion and sedimentation, chemicals, or microorganisms. Surface water pollution associated with storm water runoff can negatively impact ecosystems and reduce the aesthetic and recreational value of rivers, lakes, and other water bodies. Groundwater pollution from septic tank effluent can also limit an area’s suitability for wells. 1.4 Hydrology When local groundwater is the source of a community’s potable water, efforts must be made to ensure that on-site wastewater treatment systems and storm water runoff do not contaminate local wells. As treatment technologies continue to evolve, more highly engineered on-site wastewater treatment systems are being constructed in many formerly unsuitable locations (LaGro, 1996). These include areas with bedrock and/or water table as shallow as 20cm below the ground surface. 1.4 Hydrology: Mapping Water movement, infiltration, storage, and discharge should be considered in the site inventory of physical attributes. Hydrologic maps may also locate the primary paths of groundwater flow and the locations of groundwater discharge to the surface. 1.4 Hydrology: Mapping Maps of groundwater and local geological conditions are particularly important in land use planning for rural and urban fringe areas. Detailed site data can help in determining an area’s potential sources of potable groundwater. Surface drainage also should be mapped, as well as potential flood hazard areas. Aquifer recharge areas are also particularly important locations to identify and protect from development. To be continued… Reference: