Urban Geomorphology: Concept and Significance

1 year ago

Atiqur Rahman

17 minutes

Geomorphology is the study of landforms, particularly their nature, origin, development process, and material composition (Cooke and Doornkamp, 1990, p.1). Geomorphology is broadly defined as the study of past, present and future landforms, landform assemblages (physical landscapes), and surficial processes on the Earth and other planets (Rhoads and Thorn 1993, p. 288).

Geomorphology has a valuable role to play in the planning, development, and management of urban areas in drylands, especially in evaluating terrain prior to urban development and in monitoring changes during and after development (Cooke et al., 1982).

The type of information required depends chiefly on the local geomorphology and the responsibilities and altitudes of the relevant agencies. It will also vary with the phase of regional planning, city planning, site planning and development, and post-construction management, all required information that the geomorphologists can provide (Cooke et al., 1982).

Much work in geomorphology is of great potential value to man in his use of the physical environment (Cooke and Doornkamp, 1974; Coates, 1976; Itails, 1977), and the application of geomorphologic knowledge has increased in recent years, in harmony with growing public and political awareness of environmental problems and specifically because geomorphologists have come to give readers attention to those aspects of the subject of greatest practical application- the dynamic relations between landforms, materials, and contemporary processes (Cooke et al., 1982).

As far as Applied Urban Geomorphology is concerned, it is the study of landforms, and their related processes, materials, and hazards, in ways that are beneficial to the planning, development, and management of urbanized areas or areas where urban growth is expected (Cooke et al., 1982).

Geomorphic knowledge is significant in deciding the urban growth and urban morphometry in the geomorphological fragile zone. Since urbanization is a continuous process of urban growth, it is being affected by several factors. An urban agglomeration denotes a continuous urban spread and normally consists of a town in its adjoining urban outgrowth. The geomorphic aspect plays a great role in deciding the organizational implications.

One important qualification must be made about urban geomorphology: different aspects of geomorphology have been studied in urban areas for many years- not only by geomorphologists but also by engineers and others, some of whom may never have heard of the science. It is not, and never has been, the exclusive preserve of the geomorphologist.

For example, engineers in Los Angeles have studied sediment movement into, through, and out of the metropolis for decades, and the information they have collected has been used to predict, inter alia, the life span of reservoirs (e.g. Ruby, 1973).

Nevertheless, as the field of urban geomorphology is one in which many different aspects of the environment are closely related and can be beneficially integrated, and is also one of rapidly growing knowledge requiring greater specialization among those studying it, it is scarcely surprising that planners and engineers are increasingly either receiving geomorphological training themselves or turning to specialist geomorphologists for help in tackling problems of a geomorphological nature (Cooke et al., 1982).

A recent study suggests that there will be significant variations in the amount of urban expansion: most of the urban expansion will occur in China; some specific regions will have a high probability of urban expansion; some regions will have a low probability of urban growth.

A Bibliographic Review in Urban Geomorphology

Wolman (1967) was among the first geomorphologists to measure the physical impacts of urbanization on watersheds and stream channels. His studies found that average sediment production rates are moderate to high during pre-urban agricultural land uses, followed by a spike during construction and a decrease in sediment yield after urbanization.

Wolman’s results indicate that the channel response following urbanization is a period of deepening followed by lateral migration and channel widening. These observations of the changes in channel form are consistent with other work carried out during the same period when fluvial geomorphology in the urban environment was a developing scene.

Graf (1985) observed the effects of rapid urbanization on the fluvial geomorphology of two small watersheds near Denver, Colorado. Graf (1985) found that the initial impact for these sites was extreme aggradation and increased floodplain access due to increased rates of upslope erosion. After the watershed development, the secondary impact was that the nearly complete and impervious cover was in place, was vertical incision and down-cutting through the previously aggraded material.

Arnold, C.L., P.J. Boison, and P.C. Patton, (1982) conducted a similar geomorphic and hydrologic study of a small urbanizing watershed. The frequency of bank full discharge increased, and changes in the sediment regime were consistent with Wolman’s (1967) observation describing the effect of urbanization.

Elsewhere, in other parts of the world, studies in urban geomorphology have gained ground. Notable studies on this line worth mentioning are “geomorphology and urban development in Manchester area” by Ian Douglas. This work underlined the impact of geomorphology on river dynamics, urban growth, glacial deposits, subsidence, sewer collapse and ground conditions. There are also other works, such as urban geomorphology in Dry Lands by Cooke, R.U., Brunsden, D., Doornkamp, J.C., and Jones, D.K.C., (1982).

This study was undertaken as a consequence of serious soil erosion, landslides and widespread flooding where hundreds of people were killed and thousands of homes ruined. The dominant environmental processes responsible for this crisis are geomorphological problems, problems relating to the nature of the land surface and the forces that act upon it.

In India, the study of urban geomorphology first appeared in 1988. This study was experienced in Mussoorie and its Environs’ by H. Prasad. This study underlined the impact of geomorphology in identifying areas for the establishment of new settlements.

Attention to urban geomorphology has increased in recent years in harmony with the growing recognition of the importance of the much broader but closely related fields of environmental and urban geology (e.g. McGill, 1964; Ass. Eng. Geol., 1965; Colorado Geological Survey, 1969; Betz, 1975; Akhili and Fletcher, 1978).

Although some aspects of urban geomorphology have been considered in recent books, such as those by Coates (1971), Detwyler and Marcus (1972), Legget (1973), Cooke and Doornkamp (1974), and Leveson (1980), the rationale of the subject has not been formulated.

Urban geomorphology combines the ambient geology, landforms, and geomorphological processes with the evaluation of impacts brought to these by urbanization. The practitioners of urban geomorphology tend to concentrate on alteration, using the ambient physical environment as a baseline.

Several case studies from different parts of the world (dealing with topics such as slope instability, seismic hazards, increased flood problems, and land subsidence) have demonstrated the utility of urban geomorphology to engineers, city managers, and urban planners.

Objectives of Urban Geomorphology

Objectives of Geomorphological Appraisal Prior to Urban Development

The urban planner’s primary environmental requirement prior to urban development is a knowledge of the nature and disposition of natural resources and hazards (Cooke et al., 1982).

Therefore, the principal objectives of surveys designed to satisfy this requirement are identifying the range of possible locations of resources and hazards and analysing conditions within suitable locations to use the environmental resources more economically, beneficially, and efficiently (Cooke et al., 1982).

Within these broad objectives, geomorphologists commonly have several aims:

(1) to prevent urban growth from destroying valuable resources;
(2) to identify and evaluate land and material resources required for development;
(3) to limit the undesirable impact of urban development on geomorphological conditions;
(4) to predict the potential responses of ground surfaces to urban development; and
(5) to assess the potential impact of geomorphological hazards on the urban community.

Geomorphologists commonly adopt one or more of the three major approaches to appraisal prior to urban development.

First, by far, the most profitable and widely used approach is that of formally classifying and describing terrain features through morphological or geomorphological mapping and/or the interpretation of air photographs or other remote sensing imagery.

Second, analysis of process dynamics and landform change may be accomplished through, for example, the analysis of historical records (e.g. climatic and hydrological data of a region).

Third, the approach appraises one poorly known situation by analogy with another similar but better-documented situation elsewhere. This approach is, of course, dependent on the availability of data from analogous situations, and it provides a strong argument for the collection of information in data banks such as that envisaged by the VIGIL network (Leopold,1962) and in deserts by Bekett and others (1972; Mitchell at al., 1979).

Before urban development, the geomorphological contribution is important in providing surveys of direct use in themselves, of value as a source of derivative maps etc., and as a basis for more detailed subsequent surveys.

Objectives of Geomorphological Appraisal During and After Urban Development

During and after urban development, the urban planner normally requires to know the effects of natural events and circumstances on the urban community and the impact of urban development on the environment. It is to be noted that the primary interest of the planner is to understand the environmental consequences of urban growth.

Within this primary objective, planning and management aims include:

(1) the minimization of environmental impact;
(2) the development of local, spatial and temporal databases from monitoring studies to formulate the urban development plans; and
(3) the continued evaluation of plans, management organizations, and procedures to ensure harmonious environmental management.

The main aim of geomorphological work in this context is to monitor the dynamics of geomorphological systems to predict spatial and temporal changes in a way that allows the planner to respond effectively and in good time.

Geomorphological approaches to appraisal during and after urban development are similar to those adopted prior to development, but their relative importance changes. Field monitoring is pre-eminent, whether it is on a global scale or a city-wide scale. Monitoring often requires the establishment of fixed observation stations.

Examples of the Value of Geomorphological Information in the Planning Process

Geomorphology in City Planning

If in the planning of a new city the geomorphological surveys are carried out before the settlement of the city, then we can avoid incongruity between the environmental conditions and the city.

For example, suppose urban planners make a city plan of a city; the first city plan (we can term it is as city plan A) has an attractive spatial geometry, but it would have encountered several problems- building over scarce aggregates; hydro-compaction; flooding, sedimentation and erosion or roads crossing alluvial-fan channels; blowing sand and salt weathering. In the revised city plan (we can term it City plan B), which attempts to accommodate the implications of the geomorphological map, most of these problems are either avoided or sensibly controlled, thus saving resources, time and money.

At the scale of a whole city, a common problem is that the management of a single, natural unit, such as a drainage basin, is divided between several administrative organizations, with resulting duplication or dispersion of effort and perhaps competition and conflict. This is a problem that can be avoided if environmental criteria are used intelligently in the initial formulation of responsibilities of different authorities- although it would be naïve to assume that other factors are not usually more important in such formulations.

Geomorphology and Site Planning and Development

An excellent example of how geomorphological advice can beneficially modify site development plans is provided by Mader and Crowder (1969). He cited examples from the USA’s hilly country areas. In 1956 a residential development was proposed in the hill country of the growing settlement of Portola Valley, south of San Francisco, California.

Subsequent geological and geomorphological studies related to the formulation of the town’s general plan and zoning and subdivision ordinances revealed the nature and extent of potential slope instability in the proposed development area.

A relative slope stability map showed areas of stable, potentially moving, and moving around, and located major landslides. That map, together with other relevant information, formed the basis for a new plan in which houses were clustered on stable ridge crests, and the number of lots was only slightly lower than the maximum permitted under the general formula relating lot size to average slope; even more important, about 15 houses sites and some roads on the original plan were removed from actively moving ground, and considerably more house sites were removed from potentially moving ground.

There are numerous instances where specific geomorphological information might have helped to avoid problems and made the site-development process more efficient.

Geomorphology and Post-construction Management

It is suggested that major environmental hazards can be avoided by monitoring geomorphological processes and landform changes after construction. This can also help environmental managers and policymakers in influencing future policy planning.

Ruby’s (1973) study of sediment-yield trends in the Los Angeles River catchment is a straightforward example. The accumulation of sediment in debris basins at the mouths of mountain canyons provides rough measures of sediment yields and allows the performance of smaller check dams to be evaluated.

Ruby compared accumulated sediment yields in one canyon (Dunsmore) before and after check-dam construction with the regional norm. There are many problems associated with the data and their interpretation.

Still, regression lines relating sediment yield in Dunsmore Canyon to the regional norm for 30 years of records show that for the first 21 years, the canyon performed similarly to the regional watershed, that during the ten years following the construction of check dams sediment yield from the canyon relatively declined, and that the decline has become progressively less over time.

In the period since check dam construction, sediment yield was reduced overall by approximately half, but there now appears to be a trend back to pre-treatment yields, indicating a decline in the trap efficiency of the check dams. An alternative strategy for sediment control is required.

Before the geomorphological problems of any urban development are reviewed systematically, two further introductory themes require examination: the availability of information relevant to geomorphological studies in the urban development areas and the integration of geomorphological data into the whole assemblage of environmental data relevant to planning decisions.

Relations Between Geomorphology and Other Scientific Information of Value to Planners of Urban Areas

Geomorphological information forms but one part of the body of environmental data that may be of value to urban planners and engineers. Many environmental attributes of interest are both closely linked and highly interdependent. Data on the regional setting is primarily relevant in assessing hazards and resources and in choosing locations for development; data on site conditions is related to decisions about specific developments.

Based on recent studies, it can be argued that geomorphological surveys can provide a useful first stage in the environmental assessment, not only because geomorphology is a fundamental basis for urban development but also because studies of geology, soils, hydrology, etc., can all benefit from, and be facilitated by access to geomorphological surveys.

Geomorphology and Environmental Impact Assessment

Based on the above discussion, it is important to record that demands are increasing from planners for wide-ranging environmental reports prior to making and implementing planning decisions. The most important new requirement is not so much for resource surveys but for studies to evaluate the impact a proposed development is likely to have on the physical environment.

Although many planning authorities have required environmental impact assessment for years, recent legislation has enforced and codified the requirement in several countries, providing a substantial stimulus to the development of methods for assessment and for integrating environmental data.

The most important new law was NEPA (the National Environmental Policy Act), 1969, passed by the US government. Similar measures followed this in other countries such as Australia and Israel (e.g. Ditton and Goodale, 1972).

Assessing potential environmental impact is extraordinarily difficult because it involves predicting complex responses based on what is usually woefully inadequate scientific data. However, political necessity has prompted several attempts to develop standardized assessment techniques to streamline the production of reports, facilitate comparisons, and simplify the preparation and presentation of complex problems.

Impact of Environment on Development

This theme has much in common with the previous topic, and the techniques of environmental impact assessment mentioned there could be appropriate here, for cause and effect are intimately related to man’s relations with his environment. But the emphasis in this field commonly rests mainly on assessing natural hazards at different scales.

Thus, a major problem of environmental planning at a regional scale is establishing priorities. In this context, assessing the potential relative impact of environmental hazards is particularly important, and such impacts will vary spatially and temporally.

Conclusion

Geomorphology has a valuable role in planning, developing and managing urban areas, especially in evaluating terrain prior to urban development and monitoring changes during and after urban development. Responsibility for studying and managing geomorphological resources, hazards, and other problems may rest with various agencies within local hierarchies of management organizations.

The type of information required will depend chiefly on the local geomorphology and the responsibilities and attitudes of the relevant agencies. It will also vary with the phase of planning: regional planning, city planning, site planning and development and post-construction management, all required information that the geomorphologist can provide. In such circumstances, he must invariably be able to use a wide range of relevant data sources, some of which may be difficult to obtain.

Commonly, the geomorphological information must be integrated into a broader assemblage of environmental information that is useful to planners. Among the available methods, it is suggested that those in which geomorphological surveys provide the first stage for environmental assessment may be particularly valuable.

Urban Geomorphology: Concept and Significance

A Bibliographic Review in Urban Geomorphology

Objectives of Urban Geomorphology

Objectives of Geomorphological Appraisal Prior to Urban Development

Objectives of Geomorphological Appraisal During and After Urban Development

Examples of the Value of Geomorphological Information in the Planning Process

Geomorphology in City Planning

Geomorphology and Site Planning and Development

Geomorphology and Post-construction Management

Relations Between Geomorphology and Other Scientific Information of Value to Planners of Urban Areas

Geomorphology and Environmental Impact Assessment

Impact of Environment on Development

Conclusion

Read More in Geomorphology

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A Bibliographic Review in Urban Geomorphology

Objectives of Urban Geomorphology

Objectives of Geomorphological Appraisal Prior to Urban Development

Objectives of Geomorphological Appraisal During and After Urban Development

Examples of the Value of Geomorphological Information in the Planning Process

Geomorphology in City Planning

Geomorphology and Site Planning and Development

Geomorphology and Post-construction Management

Relations Between Geomorphology and Other Scientific Information of Value to Planners of Urban Areas

Geomorphology and Environmental Impact Assessment

Impact of Environment on Development

Conclusion

Read More in Geomorphology

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