Buffering mechanisms are important information for land use planners concerned with natural hazards. Again, the Pantanal region of Brazil provides an excellent example. This large area of swamps and lakes absorbs the Upper Paraguay River flood water and slows its arrival at the confluence with the Parana some six months later. Were it not for this buffering capacity, flood waters of the Parana and the Paraguay Rivers would reach the lower sections of the Parana River at the same time and cause catastrophic flooding. Thresholds The point at which an effect is manifested is called a threshold.
Every system has limits, and despite buffering mechanisms, the components and processes of a system will eventually fail if pushed beyond the threshold. For example, soils move despite being covered by vegetation if rainfall is intense and the slope steep, or they may remain stable under increasing grazing pressure until vegetation cover is reduced below a threshold level.
Preliminary Mission 2.
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Phase I Activities 3. Phase II Activities 4. General Recommendations. As has been said, incorporating the consideration of natural hazards early in the planning process can minimize their negative effects on development projects. A systems approach identifies hazards by looking at limiting and trigger factors, thresholds, buffers, and internal and external linkages. Information about a study area's natural hazards needs to be examined during the various planning stages see Figure The process of iteration focuses the planning studies on important factors.
Preliminary Mission The definition of the major land units river basins, sub-basins, watersheds, and life zones is required at this stage. Satellite imagery is particularly useful for this activity. Time and money can be saved by using lower resolution imagery because of the possibilities it affords to identify potential off-site influences and linkages to other systems. Conceptual modeling of the region to evaluate important internal and external linkages is also useful. Data obtained through local informants and through available literature are very important to the process.
Both upstream and downstream linkages influence on and influence from the study area should be identified. A team working at this level defines the work plan, team makeup, and terms of reference for experts to work in the next stage. This will require, for example, evaluations of flood frequencies and water surface levels by a geomorphologist or fluviomorphologist to look into the system's buffering mechanisms and to locate, identify, and quantify factors that influence the water level.
The nature and extent of streams and river valleys should also be evaluated in terms of flood hazard and flood control possibilities. Other specialists should identify threshold levels of system attributes that will ameliorate hazards and man-made features that influence the frequency, elevation, and duration of high water. Estimates of stream channel filling should be made, and slope stability and potential erosion under different scenarios should be examined.
A scale of , or larger for maps will probably be required to outline floodplains and identify problem areas where floods or other hazards need to be studied in more detail See Chapter 8. Similar evaluation of geological hazards may be necessary see Chapter The analysis of off-site and on-site seismic-prone systems will involve the identification of past earthquake intensities. The geologist will need to study the location and direction of active faults and identify probable fault ruptures. Micro-zonation technique will identify the most vulnerable areas. Similarly, a detailed study of volcanic hazards should incorporate information on the extent of previous ash falls, tephra falls, and lava flows.
The proximity of a volcano to the project area and to large bodies of water must be considered because water intensifies the violence of the eruption and accelerates the velocity of lava or ash flows. Remove structures. Low temperature By slowing down processes, allows for conservation and storage. Freeze can be lethal.
High temperature Accelerates processes, particularly respiration and recycling. Can be lethal; reduces species diversity. Heavy rains Trigger phonological events in deserts; relieve salinity in coastal environments; redistribute nutrients. Remove structures and can cause other stresses such as flooding, which affects gas exchange of wetlands sediments and turbidity in aquatic systems. Fire Makes nutrients and moisture more available; reduces competition. Removes structures. Salinity Allows higher gross productivity in mangroves up to seawater concentrations.
At values higher than 35 parts per , increases respiration rates and decreases transpiration net production rates. Volcanic eruptions Allow for better nutrient, moisture, and competitive environments. Suffocate and kill plants and animals. Flooding Removes competition; triggers phonological events.
Increases energy maintenance costs; temporarily decreases the number of taxa and individuals. Water flow Transports nutrients and oxygen; removes toxics; redistributes larvae. Removes structures; causes high energy maintenance costs to biota. Tidal extremes Redistribute nutrients, sediments, organic matter, and organisms. Expose organisms to lethal conditions. Source: Adapted from Lugo, A. Stress and Ecosystems Figure - Orders and types of soil surveys, their characteristics, data sources and uses Planning is a dynamic process that responds to the dynamics of local systems.
Land-use mapping should reflect this. Map overlay techniques are appropriate, and special hazard maps can be developed if they are not available Giuesti, ; Singer, ; see Chapters Phase II Activities The most appropriate scales for an action plan and project formulation during Phase II are between , and , In the case of floods, the geomorphologist or fluviomorphologist would further define thresholds for erosion and infiltration of precipitation, and examine changes in floodplains and peak discharge frequencies due to human intervention, both on-site and in linked ecosystems.
In the case of seismic activity, development projects should be steered away from the most vulnerable areas. A typical recommendation in the development of new areas would be to restrict uses in zones that have exhibited significant ground movement to low-density functions such as agriculture or parks. Additional suggestions should be made for mitigation measures in already developed areas. General Recommendations 1. Include specific hazard-related terms of reference for specialists working in the Preliminary Mission and in Phase I e.
These terms of reference should include the need to develop and analyze information at the points of interaction between sectoral activities. Include hazard-related terms of reference for technicians who will be responsible for project formulation in Phase II. Add the short-term participation of a geomorphologist, hydrologist, or geologist to look into areas that have been shown to be problematic during an earlier study phase.
Evaluate proposed uses of floodplains, with special attention to downstream consequences that may result from a loss of flood-water storage capacity caused by development activities. Upstream activities should be evaluated for the same reasons even if they fall outside of the region being studied. Look at the projects being considered under different scenarios of potential development in linked ecosystems.
Evaluate the influence of the projects being considered on other activities of the ecosystem, including buffering and threshold characteristics. Account for changes in the hydrologic regime that will be induced by the creation of impervious surfaces e. Be explicit in all instructions concerning land-use capability or suitability, including statements on the technology requirements for development projects.
Ecosystem Boundaries, Watersheds, and River Basins 2. Ecosystems and Associated Hazards. Ecosystem Boundaries, Watersheds, and River Basins The discussions in Chapters 8 to 12, focusing on man's relationship to each of the principal natural hazards, demonstrate that actions taken in the name of development often exacerbate hazard impact and prescribe actions that can be taken to mitigate damage.
Here the focus is on the natural services of ecosystems that serve to reduce the impact of hazards. It follows logically that one strategy of hazard mitigation is to maintain the natural capacity of ecosystems to accomplish this. Secondly, in contrast to Chapters 8 to 12, this section discusses all the hazards simultaneously in the context of the natural ecosystem in which they occur.
Again, it follows that the mitigation strategy is to maintain the natural functions of the ecosystems intact. To put the hazards in the context of ecosystems, a hypothetical composite system has been imagined which includes several ecosystems: uplands highlands, piedmont , lowlands, coastal lands, near-shore waters estuary and reef , and marine waters open sea and the development activities representative of each. Such a place would approximate a small volcanic island, part at low elevation and arid, and part at sufficient elevation to catch moisture-laden winds from the sea.
The island would experience, if at a high enough latitude, that given the variations in its elevation, both high and low temperatures extreme enough to influence development activities would occur. It would be located near an extensive fault zone and would contain a variety of development possibilities and a number of natural services that would help protect these development activities from natural hazard events.
It should be added that there are real places very much like this. The hypothetical system is made up of "watershed" or "catchment" subsystems and coastal subsystems. The term "watershed" is variously defined, and is sometimes used interchangeably with "river basin. A watershed is a system of streams that discharge all their water through a single outlet. Watersheds may range in size from a few hectares up to thousands of square kilometers, but each, whether large or small, is more or less homogeneous with respect to its geology, soils, physiography, vegetation type, and climate.
A river basin, on the other hand, is made up of a number of component watersheds, among which there may be great variation see Figure , and its hydrograph responses is therefore complex. In such systems, water and gravity are the two major natural components that integrate system structure and function the specific combination of components and processes that define a given system. Their influence on development activities in terms of the natural events they can present seismic forces, hurricanes, mass movements, etc.
Only when valuable downstream development is threatened or damaged by landslides, drought, floods, or sedimentation is attention shifted upstream or uphill. The hypothetical composite system also includes the coastal zone where terrestrial, marine, and atmospheric processes create a greater range of hazards than in most other well-defined geographic areas. Combined with the likely presence of population centers, productive agricultural lands, communication routes, buildings, etc.
Watersheds and coastal systems, of course, do not occur independently. By their very nature they are integrated and must be seen as a whole. Indeed, the concept of "expanded" watershed, which includes upstream, coastal, and near-shore characteristics, is relevant particularly where offshore hazards such as hurricanes, tsunamis, and storm surges are modified by near-shore bathymetry and coastal configuration and where the effects of inland hazards such as flash flooding and debris flows often reach coastal and near-shore areas due to the presence of steep and relatively short watersheds.
This concept of watershed can be used to illustrate an area's vulnerability to hazardous events caused by human intervention in the system. Such interventions may alter the landscape upstream, for example. But, because of the integrating characteristics of water and gravity, these alterations are not only important on-site, but are also important downstream, including near-shore areas where a sediment plume caused by upstream erosion may cover and suffocate a reef or sea-grass bed. Development activities of any kind i. Even more importantly, however, it is necessary to understand the characteristics of watersheds if a concern for natural hazards is to be included in development planning.
Given the range of natural events affecting this broadly defined hypothetical watershed, the "boundary" of its coastal or lowlands portion should remain flexible. Offshore, the boundaries can be placed at a well-defined isobath located below the depth of any bottom features capable of influencing seaborne hazards. In contrast, the watershed's uplands boundaries are readily defined in physical terms drainage areas but are often quite porous in biotic, social, and economic terms. Uplands and Volcanic Activity U1 b.
Uplands and Earthquakes U2 c. Uplands and Landslides U3 d. Uplands and Hurricanes U4 e. Uplands and Desertification U6 g. Lowlands and Desertification L6 i. Estuary and Hurricanes E4 j. Reef and Hurricanes R4 l. Open Sea and Hurricanes S4 n. The subsystems of our imaginary expanded watershed offer a surprisingly large number of natural services which can mitigate the effects of many of these natural hazards. Equally important, however, are attributes of these subsystems which can intensify the effects of natural hazard events.
Figures and indicate which subsystems of the expanded watershed contain attributes that influence the hazards summarized here.
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The paragraphs below describe how the natural services of these systems mitigate or intensify each natural hazard risk; interestingly, they are not all intuitively obvious. In the early planning phases these and other services are looked at fairly broadly, and in later iterations their roles are further and more explicitly defined.
For example, the diagnosis may say only "The natural structure and processes of the upland ecosystem in this region play a role in the control of erosion and of flooding. These might be that the "high soil water storage capacity of 'Uplands sandy loam' soil type, the transpiration from the deeply rooted species, and the high infiltration rates due to the strongly fractured structure of the sub-watershed's parent rock decrease the flood potential in storms of short duration. Figure - Map showing differences in complexity between a river basin and its watersheds Figure - Hypotethical Watersheed on a small volcanic island Diagram of a small island showing various ecosystems open sea, reef, estuary, lowlands, uplands and indicators of potential natural hazards rain, wind, and waves indicate hurricanes and flooding; volcano indicates eruptions; faults indicate earthquakes; faults and gullies indicate mass wasting.
Uplands and Volcanic Activity U1 The structures and functions of upland ecosystems that can influence the effects of volcanic eruptions are few.
However, included in what does exist are: - Relief including valley depth, slope direction and steepness , which may orient the flow of lava, ash, mud, etc. These may either intensify or mitigate the effects of a volcanic eruption depending on the location of the development activity with reference to the event. In terms of the services provided, "storage of volcanic outflow material" could be possible depending on the relief of the watershed.
The "location and extent of the rift" might intensify the hazard if development activities were sited without considering the numerous hazards that accompany volcanic activities. Uplands and Earthquakes U2 Upland ecosystems do little to mitigate the consequences of earthquakes. They may, however, intensify the consequences because of landslides caused by groundshaking. One of the more dangerous aspects of this relationship occurs in areas of current and past glacial activity and concerns the natural damming of watercourses by terminal or lateral moraines and the consequent creation of lakes.
Such dams are often quite weak and are easily breached if landslide material fills the lake. This material together with the water from the lake covered several villages as it moved down the narrow valley, causing the loss of over 10, lives. Because many upland areas do not have much level space for construction, till material is often used to create some, and the buildings put up on this unstable ground can be destroyed when the earth shakes.
Uplands and Landslides U3 The structure and function of upland ecosystems can both intensify and mitigate landslide hazards. Landslides often occur naturally in these areas owing to very steep slopes, the nature of the bedrock and overburden, the amount and regimen of precipitation, other disturbances such as natural fires which clear soil-holding vegetation, and ground shaking.
Any vegetation on the slopes of the upland system is a natural part of the soil stabilizing services, although this can only ameliorate landslides and will not stop them completely on the steeper slopes. If loose mantle overlays rock especially sedimentary rock that has been tilted off the horizontal plane, landslides will be intensified on the slope parallel to the sediment plain.
On the other hand, there are fewer and less severe landslides on the slope that runs across the sedimentary strata. Landslides occur on the parallel slopes especially if high rainfall saturates and increases the weight of the soil and lubricates the interface between mantle and base rock. In these cases even vegetation may act as extra weight and intensify a landslide.
Uplands and Hurricanes U4 Upland areas, if extensive, can serve to reduce the energy level of hurricanes, since these storms receive their energy from warm open seas. On the other hand, the heavy rainfall, in terms of both intensity and amount, can cause high runoff levels from steeply sloping landscapes. It can also saturate the soil mantle and create conditions for substantial slope failure, especially where the holding capacity of tree and shrub roots has been disturbed.
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A major example of this phenomenon occurred along the north coast of Honduras in when landslides caused by Hurricane Fifi killed thousands of people. Water is stored in lakes, ponds, streams, rivers, wetlands, soil, and snow or ice, and in aquifers when the service of groundwater recharge is also present. Further, there are services evaporation, transpiration which reduce the total amount of water available for flooding. The infiltration rate also has an influence, and this can change according to a number of physical, chemical, and biotic characteristics of the soil.
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Even the physical layout and size of the watershed or river basin can make a difference. And, depending on the nature and timing of each precipitation event, these also can mitigate flooding. Many of these same ecosystem attributes can intensify land-borne flooding. If precipitation is heavy and infiltration slow or if the soil is already saturated because of previous storms, flooding can be more frequent and its consequences more grave.
Lack of flooding storage capacity and the size and configuration of drainage can combine to increase the speed and amount of runoff. There are numerous combinations of characteristics that can influence flooding, each of which is further influenced by human activities. Figure - Attributes which can influence the effects of Natural Hazards Diagram of a small island showing major ecosystems and associated natural hazards. The text explains the potential impact of natural hazards on an ecosystem and how natural services of the ecosystem can mitigate the effect of natural hazards.
Uplands and Desertification U6 Upland areas are related to desertification in both positive and negative ways. Indeed, over much of the earth's surface, it is the presence of uplands that create the conditions for deserts because of the rain-shadow effect. That is, if upland areas force moisture-laden winds upward, two important phenomena take place: a the rising air mass cools and its moisture is released on the windward side of the uplands; and b on the leeward side the air mass loses altitude and becomes warmer in the process, and this creates desert conditions because the moisture is tightly held and precipitation is reduced Figure In Latin America the prevailing winds are generally from east to west, so that the western slopes of mountains are drier.
Exceptions occur, as in southern Chile, Argentina, northern Ecuador and Columbia, where the phenomenon is reversed: the western slopes of the Andes receive higher precipitation and the eastern slopes receive less, becoming drier as one moves eastward. Often, the dry areas occur fairly close to relatively wet areas, from which their populations and development activities can be supplied with water. The combined effect can be that high tides act as barriers damming river and stream outlets to the sea, so that any heavier than normal flow caused by upstream runoff will overflow banks.
The normal flow from uplands tends to spread out upon reaching lowlands, where slope is less pronounced and valleys are wider. Furthermore, water flow from the uplands loses some of its energy on reaching the lowlands, causing much of the sediment load of the river or stream to be dropped. This fills in the river bed with sediment and may even raise its level above the surrounding lands.
If high water breaches the natural levees built up through this process, extensive areas may be flooded. On the positive side, coastal areas, especially those having substantial estuaries, reefs, or wetlands, can absorb significant quantities of water and the wave energy accompanying sea-borne events which cause flooding see below E4, E5, R4, and R5. Lowlands and Desertification L6 As was noted in U6 above, lowland areas are often in a rain shadow of an upland area, which means that they can easily succumb to desertification. What is MDS? LibraryThing's MDS system is based on the classification work of libraries around the world, whose assignments are not copyrightable.
MDS "scheduldes" the words that describe the numbers are user-added, and based on public domain editions of the system. Wordings, which are entered by members, can only come from public domain sources. Where useful or necessary, wording comes from the edition of the Dewey Decimal System.
Language and concepts may be changed to fit modern tastes, or to better describe books cataloged. CLM includes long-form articles, events listings, publication reviews, new product information and updates, reports of conferences and letters. Exceptional customer service Get specialist help and advice. Traces the historical growth of design approaches involving natural processes, and presents an introduction to the principles, methods, and techniques that can be used to shape landscape, land use, and natural resources in an ecologically sensitive and sustainable manner.
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