Maps as Site Analysis Tools

1
Maps as Site Analysis Tools

• Overlaying Slope, Drainage, Soils, Vegetation
  Maps to Identify Development Opportunities
  Constraints

2
Todays Agenda

• Reading maps
• Location
• Topographic
• Soils
• Vegetation
• Synthesizing map info
• Slope
• Drainage

• Making suitability maps
• Graphic overlay analysis (Ian McHarg)
• Computer overlay models (ArcView Spatial Analyst)

3
Locational Structure
4
The U.S. Grid
5
USGS 7.5 Minute Quads Contours, Features
Scale 124,000 (about .4 mile to the inch)
Contour interval 10 feet
6
Reading a Topo Map
7
Interpreting Contours
8
Interpreting Contours
9
Determining water flow direction
Which way does water flow? Hint always
downhill!!
10
Why Investigate Soils?
11
(No Transcript)
12
(No Transcript)
13
Horizons

• 0 Horizon - Organic
• A Horizon - Mineral Horizon mixed with organics
• B Horizon - Mineral Horizon changing layer
• C Horizon - Mineral Layer
• R Horizon - Consolidated rock

14
Cross Section of Soils Horizon
15
Cross Section with Soil Types
16
Erosion Forms New Horizons
17
Soils Surveys

• Report defines
• Types of soils
• maps of soils
• Suggested use and management

18
U.S. Natural Resources Conservation Service (old
SCS)
Scale usually 1 20,000
Soil type slope
19
Soil Properties of Concern

• Bearing capacity
• Shrink swell
• frost penetration
• slope failure

20
Bearing Capacities

• Bed Rock 200 kips/sq ft
• Sedimentary Rock 30
• Compacted gravel 20
• Loose gravel 8
• Stiff clay 8
• Soft clay 2
• (1 kip 1000 pounds)

21
Angles of Repose
22
Soil Engineering Ratings

• Building sites (stability, bearing capacity)
• Sanitary facilities (septic systems)
• Construction materials (sand, gravel)

• Drainage (wetlands, floodplains)
• Recreational areas
• Compaction characteristics
• Erosion potential
• pH

23
Shear, Compression, Workability, Permeability
24
Vegetation Tree Types
Darker mature woods specimen trees
25
Synthesizing Slope from Topo

• Slope maps are derived by converting distance
  between contour lines into percent (planning use)
  or degree (engineering use) classes or intervals
• Unconstrained (0-14)
• Moderate (15-25)
• Steep (26 or greater)
• Closer the contour lines, steeper the slope!

26
Visualizing Slope
25 slope rises 25 feet in 100 feet horizontally
27
Deriving Slope

• Slope vertical rise in feet for every 100 feet
  of horizontal distance
• Slope Run/Rise x Contour interval
• Classes
• Unconstrained 0-15 100/15 x 1 6.7 between
  1 contours (13.4 for 2 contours)
• Moderate 15-25 100/25 x 1 4-6.7
• Steep 26 up 100/26 x 1 3.9 or less

28
Making a Slope Map by Hand
29
Deriving Drainage from Topo

• Water runs downhill (until Law of Gravity
  repealed) follows shortest path (perpendicular
  to contour lines)
• Water runs off ridges collects in swales,
  streams, ponds, floodplains
• Watersheds basins bounded by ridge lines
• Contours in swales point upstream, indicate
  direction of water flow

30
Making a Drainage Map
Ridge line
31
Site Suitability Analysis

• Purpose
• Identify map separate ecosystem components
  (soil, vegetation, hydrology, etc.)
• Understand relationships among components (e.g.,
  how slope soil interact to affect erosion,
  building sites, etc.)
• Determine suitability of site areas for various
  land uses, based on component combinations
• Not a design plan but an indication of
  opportunities and constraints
• History
• Developed in 1960s by landscape architect, Ian
  McHarg (author of Design With Nature)

32
Suitability Analysis Approach

• Overlays ecosystem components in order to
  estimate development suitability
• Highlights both
• Site amenties (nice views, water, trees,
  orientation, buildable areas, good access)
• Site constraints (bad views, steep slopes, wet
  areas, unstable soils, noise, poor access)

33
Site Suitability Map
34
From Design With Nature to GIS

• McHarg-eyeballing
• overlaid sheets of tracing paper (1 for slope,
  soils, etc.),
• determined suitability by visual inspection
  (e.g., darkest areas),
• drew composite suitability map

• GIS-computing
• uses computer to overlay registered layers of
  digital data,
• can add weights if desired,
• determines suitability mathematically,
• makes composite map

35
Suitability Model Opportunities

• Slope moderate, unconstrained (0-15)
• Drainage not in drainage courses, floodplains
• Soils stable, well drained
• Vegetation hardwoods

• Model additive, weighted/ unweighted
• Suitability
• High (flat, accessible, dry, stable, views, etc.)
• Moderate (medium slope, accessible, mostly
  dry/stable, etc.)
• Low (steep, wet, poor soil, difficult access)