Land-Use Planning and Engineering Geology Chapter 19

Land Use Planning – Why? Safety? Is it the best use of a tract of land? Will the intended use be a misuse of the land? Are the resources required (water – for example) for the intended use available? Is there a potential for pollution from this intended use of a tract of land?

Conversion of Rural Land Between 1997 to million acres of rural land were converted to developed uses The rate of development is accelerating and the amount of available land has not increased Some lands will not support any or all forms of uses

Figure 19.1 a Land use in the United States

Figure 19.1 b Land converted to developed land

Considerations in Planning What is the optimum use of a tract of land? We must consider: –Biological factors –Ecological factors –Geological factors –Economic factors –Political factors –Aesthetic factors

Land-Use Options Multiple Use – using the same land for two or more purposes –Parks or green areas used for recreation and to catch fresh water during a storm to allow it to infiltrate into the ground water Sequential use – utilize the land for two or more different purposes, one after another –Mines are used to provide the commodities found in the subsurface, then they are re-used for sanitary waste dumps, storage, or in-filled for parks

Figure 19.3 Multiple land use

Figures 19.4 a and b Sequential Land Use

Federal Government and Land-Use Planning Historically, federal lands are not equally distributed throughout the states Originally, federal emphasis was on resource development rather than preservation Federal lands fall into two categories: –Lands intended for preservation (national parks and wilderness areas) –Lands intended for multiple use and compatible use such as grazing, logging, mining, exploration and drilling for petroleum (national forest)

Figure 19.5 Land ownership by state, 1997

Maps as a Planning Tool Land use planning requires abundant information, maps often provide much of the information: –Topography, bedrock geology, surface materials and geology, soils, depth to ground water, vegetation, population information, location of fault zones and flood plains, and more –Maps can assist planners in long term planning, establishing restrictive zoning for earthquake or flood hazards, avoidance of other hazards as well

Figures 19.6 Map representation of geologic considerations

Figure 19.7 U.S. land-use classifications

Maps as a Planning Tool Computers have aided planners –Information required by planners is voluminous –Computers have played an increasing role for planners to manipulate large volumes of quantitative information –Geographic Information Systems (GIS) allow planners to manipulate the data to see and use what data is useful to a planning task while minimize, or obscuring, unimportant data –GIS can allow a planner to see distinct “layers” of information that are important to the decision making process

Figure 19.8 Digitized maps can represent data

Figure 19.9 a composite map for land-use planning

Figure a

Figure b

Figure c

Engineering Geology Geologic factors and considerations vary depending on the site and the project A few considerations for a major project may include: Rock types present in project area, are they uniform or variable Are they fractured or faulted? If they are, are the faults active? Is there a landslide risk? What types of soil or soils are present? Are they suitable for the project? What are the hydrologic factors? Surface and subsurface The list is nearly endless

Figure a Failure of structure on unstable soil

Figure b Relative magnitudes of loss of life and property damage from various geologic hazards

Engineering Geology Major projects often encounter major obstacles –Alaskan Oil Pipeline Project (1300 km long) Spans a variety of geologic settings (rock types, structures, faults, slopes, soils, mountains, streams) Active earthquakes, seasonal flooding, animal migration routes – all required solutions Climate factors – North Slope is very cold with permafrost and a variable permafrost table

Figure a

Figure b

Figure permafrost and permafrost table

Figure Differential subsidence of railroad tracks due to partial thawing of permafrost

Role of Testing and Scale Modeling Models are physically constructed (at a reduced scale) Models may be tested in a computer Failures of a variety of structures can be tested – dams, bridges, or earthquake resistant buildings

Fig Scale modeling

Case Histories Leaning Tower of Pisa: the flow of the unstable soft clay layers Panama Canal: Dipping layers of young volcanic rocks, lava flows, and pyroclastic deposits and dipping beds of shale and sandstone Boston’s “Big Dig”: Glacial sediments and weakly metamorphosed mudstone

Fig Geologic factors complicated construction of the Panama Canal

Figure Boston’s “Big Dig”: Slurry walls keep excavations from collapsing and nearby building foundations from failing

Dams - Failures and Consequences A catastrophic dam failure can impact many cities, thousands of lives, and cause millions of dollars worth of property damage St. Francis Dam: coarse sandstones; schists and mica-rich metamorphic rocks; a fault Baldwin Hills reservoir: an active fault zone Three Gorges Dam: control the flooding, enhance navigation, and produce energy

Figure a Hoover Dam

Figure b A regional overview of Hoover Dam

Figure Failure of the St. Francis Dam in California

Figure Benefits and issues in dam construction