Monday, March 26, 2007

Organization of The Seminar

Chapter I : Describes Urban Hydrology, The Scope of Urban Hydrology, Objectives and Scope of Study, and Organization of The Seminar.

Chapter II : Gives details about Desk-top Methods for Urban Drainage Design; The Rational Method for Surface Drainage, Kinematic Time of Concentration Formulas, The Kinematic Rational Method and Storm Sewer Design by The Rational Method.

Chapter III : Explains about Storm Water Management Model-software; Introduction and SWMM’S Conceptual Model.

Chapter IV : Explains about SWMM Application to Urban Drainage Planning; Example Study Area Map, Explanation of Input Data and Output.

Chapter V : Summary & Conclusion.

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Objectives and Scope of Study

1. To understand the issues involved in the planning of urban drainage.

2. To understand basic theory of an operational model, and related software (Storm Water Management Model) for its potential use in simulation of an existing drainage system and in planning of a new drainage system.

3. To understand how to use SWMM software (input data as per requirement) and applied an various illustrative examples.

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The Scope of Urban Hydrology

Several authors, including Savini and Kammerer (1961), Leopold (1968), Hall (1973) and Cordery (1976), have described the changes in flow regime which occur when an initially rural catchment area is subject to urbanization. The particular aspects of urbanization which exert the most obvious influence on hydrological processes are the increase in population density and the increase in building density within the urban area. The consequences of such changes are outlined diagrammatically in FIG. 1.4.

FIG. 1.4. The effects of urbanization on hydrological processes.

As the population increases, water demand begins to rise. This growth in demand is accelerated as standards of living are raised and compounds the problem of developing adequate water resources – the first of the major hydrological problems.

Once the initial stages of urbanization have passed and sewerage systems are installed for both domestic and surface water drainage, the amount of waterborne waste increases in response to the growth in population. However, the resultant water quality changes are intimately linked with the consequences of the increase in building density. As the latter rises, the extent of impervious area also increases, the natural drainage system is modified and the local microclimate changes. Owing to the larger impervious area, a greater proportion of the incident rainfall appears as runoff than was experienced when the catchment was in its rural state. Furthermore, the laying of storm sewers and the realignment and culverting of natural stream channels which takes place during urbanization result in water being transmitted to the drainage network more rapidly. This increase in inflow velocities directly affects the timing of the runoff hydrograph. Since a larger volume of runoff is discharged within a shorter time interval, peak rates of flow inevitably increase, giving rise to the second of the major hydrological problems-flood control.

The inadvertent changes in the microclimate which accompany the growth of urban areas may at first sight appear somewhat irrelevant in comparison to the changes in the hydrological cycle brought about by urbanization. Nevertheless, further consideration of the available evidence, as presented by Landsberg (1981a, b), for example, shows that, since all aspects of climate are affected to some extent by urban development, some attention should be devoted to the possible consequences of such changes in terms of infrastructure design. For example, in drainage design practice, particular importance is attached to the frequency of heavy rainfalls within predetermined durations. Changes in the relationship between rainfall depth, duration and frequency may therefore alter the degree of protection afforded by engineering works subsequent to their design and construction. Possible allowances for such changes are most conveniently treated as a supplementary aspect of the flood control problem.

As FIG. 1.4. demonstrates, the water quality aspects of the hydrologi¬cal cycle are affected by both the rise in population and the increase in the extent of the impervious area. Since the volume of runoff becomes larger with the onset of development, the amount of soil moisture recharge is reduced. Consequently, less water is likely to percolate into any aquifer underlying the urban area. Between storm events, the baseflow within the natural drainage system is derived from such subsurface storages. Low flows may therefore be expected to decrease as the urbanization of an area proceeds. Unfortunately, this decrease occurs simultaneously with the increase in the volume of waterborne wastes referred to above and the deterioration in the quality of stormwater runoff as contaminants are washed from streets, roofs and paved areas. The disposal of both solid and waterborne wastes may also have an adverse effect upon groundwater quality. The degradation of the quality of the flows in both the drainage network serving the urban area and the underlying aquifers gives rise to the third of the major hydrological problems - pollution control.

In summary, the process of urbanization may be seen to create three major hydrological problems: the provision of water resources for the urban area that are adequate in both quantity and quality; the preven¬tion of flooding within urban areas; and the disposal of waterborne wastes from urban areas without impairing the quality of local water¬courses. Of these three problems, that of water supply forms part of the wider subject of water resources development, and is beyond the scope of this text. Nevertheless, two distinct attitudes to the develop¬ment of water resources for rapidly growing urban areas may be identified in current practice.

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The Definition of Urban Hydrology - Part.2

Although FIG. 1.1 in below is useful in imparting the essential features of a water cycle driven by the excess of incoming over and outgoing radiant energy, this representation fails to provide an adequate framework that can be obtained by adopting the so-called system notation, in which the paths of water transport link the major sources of moisture storage, as presented by Dooge (1973) in FIG. 1.2.

FIG. 1.2. The hydrological cycle in system notation
(modified from Dooge, 1973).

A closer examination of FIG. 1.2. reveals that hydrologists do not in fact concern themselves with the whole of the hydrological cycle. The oceans are the province of the oceanographer, the atmosphere is studied by the meteorologist, and the lithosphere by the geologist. What remains is commonly referred to as the land phase of the hydrological cycle. This subsystem, whose limits are shown by the broken line in FIG. 1.2., receives an input of precipitation, P, and produces outputs in the form of evaporation, E, and river flow, Q. Further subdivision is possible in order to demarcate the interests of other specialist groups. For example, the soil scientist may confine his interest to the upper soil horizons, which receive water by infiltration, F, or capillary rise, C, and lose water by evaporation, E, deep percolation, R, or throughflow, Qi. Nevertheless, despite the improvement in the level of comprehension afforded by FIG. 1.2. over FIG. 1.1., an additional important element is missing – that of the influence of man.

Since time immemorial, man has manipulated his environment, and therefore the land phase of the hydrological cycle, for his own purposes. Wildscape has been cleared for agriculture, forests have been felled, swamps have been drained and, most important of all, towns and cities with all their associated infrastructure have been created in what were once rural areas. Over the last 25 years, increased attention has been devoted to the hydrology of land use changes in general, but only the process of urbanization has given rise to a new and recognizable branch of the subject – urban hydrology.

Perhaps the most obvious definition of urban hydrology would be the study of the hydrological processes occurring within the urban environment. However, further consideration of the hydrological cycle of an urban area, as presented in FIG. 1.3., soon reveals the inadequacy of this simplistic conception. The natural drainage systems are both altered and supplemented by sewerage. The effects of flooding are mitigated by flood alleviation schemes or storage ponds. In the initial stages of urban development, septic tanks are employed for the disposal of domestic wastes. As the urban area grows, foul sewerage systems discharging to sewage treatment works are installed, and the treated effluent is returned to local watercourses or even the ocean. Initially, water supplies are drawn from local surface and groundwater sources at minimum cost, but as the population increases the demand for water rises, further supplies may only be obtainable from more remote locations. Both waste disposal and water supply therefore extend the influence of the urban area well beyond its immediate boundaries. Urban hydrology may consequently be defined in more appropriate terms as the study of hydrological processes both within and outside the urban environment that are affected by urbanization.

FIG. 1.3. The urban hydrological cycle.

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Wednesday, March 21, 2007

The Definition of Urban Hydrology - Part.1

Hydrology may be defined as the physical science which treats the waters of the Earth, their occurrence, circulation and distribution, their chemical and physical properties, and their reaction with the environment, including their relation to living things (UNESCO, 1979).

These words serve to emphasize two particular aspects of the subject: its interdisciplinary nature, which embraces physical, chemical and biological as well as applied sciences; and its concern with the spatial and temporal distribution and movement of water in all its forms.

The latter is implicit in the concept of the hydrological cycle, which illustrates the multifarious paths by which the water precipitated on to the land surface finds its way to the oceans, where evaporation provides the supply of moisture for the renewal of the process.

The hydrological cycle is commonly presented in pictorial form, of which
FIG. 1.1, adapted from Todd (1959), provides a typical example.

FIG. 1. 1. The hydrological cycle in pictorial form (source Todd, 1959).

The Hydrological Cycle

From the time the earth was formed, water has been endlessly circulating. This circulation is known as the hydrologic cycle. Groundwater is part of this continuous cycle as water evaporates, forms clouds, and returns to earth as precipitation.

Surface water is evaporated from the earth by the energy of the sun. The water vapor forms clouds in the sky. Depending on the temperature and weather conditions, the water vapor condenses and falls to the earth as different types of precipitation. Some precipitation runs from high areas to low areas on the earth's surface. This is known as surface runoff. Other precipitation seeps into the ground and is stored as groundwater.

Think of groundwater as water that fills the spaces between rocks and soil particles underground, in much the same way as water fills a sponge. Groundwater begins as precipitation and soaks into the ground where it is stored in underground geological water systems called aquifers. Sometimes groundwater feeds springs, lakes, and other surface waters or is drawn out of the ground by humans. The water then can evaporate, form clouds, and return to the earth to begin the cycle over again. be continued --> Part. 2

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Tuesday, March 20, 2007

Urban Drainage Planning


The rainfall-runoff process in an undeveloped area is primarily determined by the natural surface detention, infiltration characteristics, and the drainage pattern formed by the natural flow paths. The type of the surface soil, the nature of vegetative cover, and the topography are the governing factors. The natural rainfall-runoff process is altered in urbanizing areas. Part of the land surface is covered by impervious material due to urbanization. The water courses are cleared, deepened, and straightened to improve their conveyance capacities.

New man-made drainage facilities are added to the drainage system. A typical urban land cover consisting of impervious rooftops, streets, and parking lots allows far less surface retention and infiltration than an undeveloped land. Moreover, stormwater runoff occurs over smooth, impervious surfaces, and in man-made or improved natural channels with increased velocity. As a result of these factors, urbanization increases the stormwater runoff volumes and rates, and possibly causes flooding of downstream areas. It can also accentuate downstream channel erosion.

In response to these critical problems, engineers and scientists have developed many innovative techniques to analyze urban hydrology. They have also designed many innovative structures to control urban flooding and improve stormwater quality. These analysis techniques and design structures rely heavily on numerical methods and computer models. Thus, desktop methods and empirical models are giving way to new, physically based techniques that are embedded in modern computer software.

Storm Water Management Model (SWMM) is a rainfall runoff simulation model which can be used for single event or long-term (continuous) simulation of runoff quantity and quality from primarily urban areas. Computer based Storm Water Management Model (SWMM) can be used in several practical applications. This study provides an understanding of urban hydrology, i.e. how to plan urban drainage. The latest version of SWMM 5 software developed by US EPA has been studied and applied an various illustrative examples.

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Water Resources Engineering

Preface: Water Resources Engineering

Effective management of water resources, locally, regionally, and globally, is crucial for human welfare, economic prosperity, and environmental vitality. The profesional field of water resources engineering is concerned with solving problems and meeting needs associated with municipal, industrial, and agricultural water supply and use, water quality in streams and aquifers, erosion and sedimentation, protection of ecosystems and natural resources, recreation, navigation, hydroelectric power generation, stormwater drainage, and flood damage mitigation.

Water resources engineering involves people, natural resources, and constructed facilities. In meeting the water-related needs of society, water resources engineers both:

1. Formulate and implement resource management strategies, and

2. Plan, design, construct, and operate structure and facilities.

Development and management of the natural resource water are essential for human survival and prosperity. Water management is also integrally linked to stewardship of land and environmental resources. The water-related infrastructure of a city, region, or nation includes river regulation structures, wells for pumping groundwater, storage and conveyance facilities, treatment plants, water distribution networks, waste water management systems, flood damage reduction measures, erosion mitigation practices, stormwater drainage systems, bridges, hydroelectric power plants, and various other constructed facilities.

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