e-Journal Earth Science India: www.earthscienceindia.info Popular Issue, April, 2010

Urban Geology:Urban Geology:Urban Geology:Urban Geology: Possible Anatomy of a New Thrust Possible Anatomy of a New Thrust Possible Anatomy of a New Thrust Possible Anatomy of a New Thrust

Area in the Indian ContextArea in the Indian ContextArea in the Indian ContextArea in the Indian Context

Prof. S. J. Sangode

The branch of ‘Urban geology’‘Urban geology’‘Urban geology’‘Urban geology’ is in its infancy and is generally considered as offshoot to Geotechnical Engineering or sometimes specialization within Environmental Geosciences.…………demands of predictive modeling as preparedness to natural disasters like flooding, draught, earthquake and tsunami; that are more urgent in the areas of higher population density needs a better geological input.

Rapid urbanization in developing countries like India is directly related to

deterioration of the geo-, eco-systems. It is, therefore, urgent to understand the urban geo-

system and generate the data and awareness amongst planners to produce long ranging,

sustainable and disaster-proof growth. The current status of work in this area is mainly

focused at estimating the levels of pollution, land use planning, disaster management and

other remedial measures apart from the greater thrust on urban hydrology. In the absence

of geological factors, several studies on urban environments may remain two dimensional,

and the urban development as short sited. The bedrock geology plays a vital role in ground-

and surface water circulation, while the soils act as interface and hosts to the long term

residence of heavy metals and solid waste permanently altering the natural course of

pedogenesis. The geological history of the urban area determines the articulation of the

atmospheric as well as groundwater circulation; both natural and anthropogenic. Locations

to long term residence of heavy metals and solid wastes are largely determined naturally by

several geological and geomorphic agencies such as ground slope, soil cover, bedrock

structural elements and their interaction with surface waters.

Ignorance on sustainable and wise utilization of the natural resource system made

the metropolitan regions (both Urban and Sub-Urban) quite vulnerable, affecting physical

and mental health of the society. Few urban areas have medically safe potable waters and

healthy breathable airs. How these factors are concerned to geology; and the ways the

knowledge of geology can help to solve some of these problems should be of great concern

to Urban Geologist. The existing texts on the branches such as geotechnical and engineering

geology traditionally grown as the subjects under Civil Engineering have focused more upon

the technical aspects of suggesting remedial measures by assessing the local ground

conditions mainly aimed at building structures. On the other hand the geological streams

with high societal implication have concerned the issues like disaster management, landslide

mitigation and seismic hazard zonation with little emphasis upon holistic approach focused

at urban geological problems. Therefore here is a need to integrate and discuss all these

aspects under single roof of urban geology.

A Methodological Approach to Urban Geology

Every major city needs to be ready with relevant models and plans for natural

disasters like earthquakes, tsunami, storm, landslides, flood and draughts, groundwater

e-Journal Earth Science India: www.earthscienceindia.info Popular Issue, April, 2010

articulation and the long term residence effects of pollutants; and also the modalities to

avoid hindrance with the natural ecosystem. This however needs a good futuristic database

using correct and authentic methods towards successful planning and predictive modeling.

Therefore a possible methodology of Urban Geology can be suggested in this article.

Urbanization alters the morphology (texture) of ground and original landforms

followed by outward peripheral growth of similar process. One of the worst phenomenon is

the encroachment of floodplains of a river flowing through the city. The river banks are

often reclaimed by settlement and construction to the extent of 100% destroying the

natural floodplains. Floodplains are the essential part of a river which accommodates the

floodwaters during rainy season and deposits the fine silt and mud as the coarser sediment

load is carried away by the channel. Although the administrative deadlocks do not allow to

reclaim the natural floodplains, geological acumen can be used to develop a

regulatory/recycling design system (e.g., of canals) to relief some of the seasonal problems.

Fig. 1: (a) A setting of polluting sources in the backdrop of settlement and a background of

major geological structure in the form of ridge (Chembur area of Mumbai), (b)

Residential area in a relative depression due to mountain ridges (in the back) and

raised grounds (eroded ridges) in the front with garbage dumping (Mumbra area),

(c) dynamic nature of a seasonal rivulet scouring the bedrocks (Owe Camp area,

Navi Mumbai), (d) The Mula River in Pune with encroached floodplains and

enhanced stagnancy of waters.

e-Journal Earth Science India: www.earthscienceindia.info Popular Issue, April, 2010

Every city has its unique geo-anthropologic problems that may be immediately

visible (such as Fig. 1) or inevitable in future. Several regions in India are susceptible to

flooding, draught, earthquake and tsunamis, landslides and cloud-bursts. Therefore a

common strategy of observations needs to be followed by the intrinsic/area specific

problems. Enumerated below are therefore some of the broad geo-anthropologic

observations to be learned by a student of urban geology.

I. Study of imageries, district resource maps and toposheets to get a regional

glance of the urban area. Some of the older toposheets may be useful to obtain

the pre-urbanized information.

II. Ground Characterization of Urban areas by bedrock/outcrop composition,

structural elements and its relation to regional geology connections, soil types

and soil-subsurface thicknesses and relation to topography; and the preparation

of maps and profiles. The term soils is used broadly to include the transported

soils and sediments apart from the in-situ soils.

III. Preparation of DEM and slope maps as overlay to the maps prepared in II,

inorder to understand the seasonal surface water run-off and its relation to

ground permeability.

IV. Understanding common meteorological parameters e.g., wind speed, wind

direction and wind profiles; in relation to topography as well as polluting sources.

V. Formation of grid and sampling in each grid unit under the four layer model of

bedrock, topsoils, dust and aerosols, and rain waters atleast for two seasons

(i.e., pre- and post monsoon with the mid-monsoon rain water). Developing a

sample repository is also valuable.

VI. Sampling the profiles of lakes, river terraces and soils for historical projections

and finding out the trends/levels of pollution etc.

VII. Data analysis by geochemical, environmental magnetic, clay mineral, grain size

and other necessary methods for the samples collected in the grid.

VIII. Presentation of data more suitably by GIS methods and in integration to the

satellite imageries. A data repository is always good as utility and for further

studies.

Urban Geological Set up

In the commonality of the geology and cultural context, majority of the urban

settlements have flourished along rivers, in valleys, at the coasts, on alluvial plains, in

foothills, deserts, mountain slopes and mountain tops. Majority of these settings are

alarming for the geological reasons such as flooding/draught, sea level rise, earthquakes,

tsunami and landslides. A geological insight is, therefore, necessary in order to visualize,

assess, predict and arrest the deteriorations of natural systems and develops the

preparedness to natural disasters; and each of the urban area needs to be dealt separately

as case study. Below we discuss the most common setting in Indian context- Cities

developed along rivers sides and valleys.

Urbanization along river-sides is traditionally (/historically) the most common

phenomenon due to want of fresh water for civilization. In this typical environment, the

rivers can be divided into less polluted upper reaches (catchment) to the highly polluted

lower reaches. As the river traverse through the city; it is choked by overexploitation of

water and addition of solid wastes increasing the viscosity and density of the water,

reducing the ground porosity from thalweg to flood plain area. Further the encroachment of

natural floodplains by settlement and construction constrains the natural behavior of rivers

(e.g., Fig. 1). This results in the enormous increase in energy conditions as the river enters

to city during rainy seasons. While during fair weather conditions there is great increase in

e-Journal Earth Science India: www.earthscienceindia.info Popular Issue, April, 2010

the stagnancy of waters within the channel as well as small ponds formed over flood plain

during floods. This cultivates organic matter and increases inhospitable conditions by

flourishing the insects, bacteria, viruses and BOD during the non-rainy season. The pollution

related aspects may be dealt in detail by ecologist and environmental chemists, while the

urban geologist is concerned over understanding of the altered river dynamics.

Fig. 2: (a) A cartoon depicting the general setting of a riverside city, that can be subdivided

into three zones as shown. (b) A sketch of probable solution to the surface and

groundwater deterioration. Practicality of such solution depends upon geological

acumen to be developed by an Urban Geologists and conveyed to planners.

The natural floodplains are forcibly reduced in urban areas but immediately regained

immediately in the outskirts (see Fig. 2). During monsoon, as the river enters into the city

from its natural upper reaches (catchment), it experiences a competitive mode to

accommodate its flow over the narrow encroached floodplain-channel system raising the

base level. It eventually attempts to incise (/scour) deeper apart from gushing into the flood

plains. However since the channel itself is already filled with effluents and higher viscosity

muds, the sharp scoured channel valley is insufficient to accommodate the waters and it

gets spilled over the encroached floodplains entering into the city. This creates a dynamic

situation creating turbulence. The spilled over water enter back to the channel adding to

flow velocity and turbulence. Some of the spilled-over waters however may remain over the

flood plains forming small ponds with stagnancy of waters due to low permeability of ground

e-Journal Earth Science India: www.earthscienceindia.info Popular Issue, April, 2010

in this zone. The river when approach to its lower reaches, it experiences relaxation due to

regaining the space for its natural floodplains. This causes sudden drop in velocity and

hence immediately deposits the sediment load brought from the city. This sediment load

saturated with the city effluents and solid waste then dumped in the outer margins of the

city in large scale creating conditions like mud flats (e.g., the Yamuna River in Delhi).

During fair-weather conditions (Summer and Winters) the flow velocity and volume is

reduced, so also the sediment load and cutting capacity, and the river makes natural

incision within the floodplains maintaining the channel. Further since the ground porosity is

reduced in the zone of urbanization, more percolation and recharge occurs in the immediate

lower and upper reaches creating boundary conditions that may lead to great fluctuations in

the groundwater levels year after year.

Cities developed in the valleys are also greatly influenced by fluvial system and

precipitation. Large cities are often grown in the broad open valleys surrounded by irregular

smaller hills and the river confluences. Valleys in general have natural depression in the

central part that also marks the areas of high natural permeability and water recharge

capacity. Unfortunately these central portions of the city are always thickly populated and

the conditions are reversed. Since all the slopes converge into the central portion they are

also areas of sediment deposition. Since these soils and sediments are loaded with

anthropogenic pollutants throughout the year, there is higher transport and residence of

pollutants towards this part of the city. On the other hand the peripheral parts of the city

are naturally cleaned by the precipitation every season.

The scope of Urban Geology

Environmental degradation resulting from rapid urbanization compels us for better

planning of the georesources for their longer and safer use. Ignorance on sustainable and

wise utilization of natural resources can lead to the irreversible and vulnerable damages to

the ground affecting both the physical and mental health. Very few urban areas have

medically safe potable waters and healthy breathable air. How these factors are concerned

to geology and how the knowledge of geology can help to better living conditions is the way

an urban geologist needs to think. On the other hand every major city needs to be ready

with models for natural disasters like earthquake, tsunami, storm, flood and draughts and

ready plans to face these vagaries of nature.

Urban geology can provide geoscientific information necessary for long term planning

in densely populated areas to be used by engineers, planners, decision makers, and the

general public. Urban geological studies rely upon diverse branches of earth sciences such

as geomorphology, meteorology, geohydrology, engineering geology, remote sensing,

geochemistry, stratigraphy, medical geology, ecology etc. It strives upon three-dimensional

information with characterization of variables in order to explain the geological processes

operating under dynamic equilibrium of the local environments. The geological information

derived from various sources such as geological maps, borehole logs, hydrogeological

reports and digital elevation models, if compiled in a digital format can be used as database

and the samples collected in grid as repository. Such a framework can be useful to

benchmark the levels of deterioration for the succeeding years.

Urbanization alters the original landform morphology followed by its outward growth

besides changing the patterns of surface water and air circulation. Apart from these

spasmodic changes, the episodic natural phenomena plays a significant role in urban

geology. Heavy rain-induced flooding, earthquakes, storms and tsunami are the serious

unpredictable concerns for an urban geologist. Further, the urbanization has a major impact

on groundwater recharge and aquifer dynamics especially by import of large quantities of

e-Journal Earth Science India: www.earthscienceindia.info Popular Issue, April, 2010

water for supply. Extensive use of the ground for effluent discharge and waste disposal and

large-scale intra-urban groundwater obstractions may lead to irreversible changes in

groundwater dynamics. Aquifer depletion, saline intrusion, contamination, land subsidence

or locally rising groundwater levels needs to be assessed. All these issues are greatly dealt

under Urban Hydrology and in the scenario of the essential knowledge of geology in it; this

can be part of urban geology itself.

Often layers of encrustations are formed in the ground by historical input of affluents

as the city evolves over the years. Therefore knowledge upon ecrustation stratigraphy can

lead to some of the vital information within urban geology. Instrumental and mathematical

relations are to be developed to assess various inter-parametric relations in the given urban

setup. Pollutants accumulate in certain zones throughout the year and are

recycled/transported more efficiently during monsoon. It is essential therefore to find the

zones of accumulation (seasonal dumping) in order to retreat them and arrest the further

residence effects especially of heavy metals.

At this juncture, therefore, it is essential to explore the holistic approach and scope

of the ‘Urban Geology’ with above prospects before its incomplete hijack by other dynamic

streams of science. A greater discussion amongst geoscientists for its utility in the race of

urbanization and the attention of funding agencies is necessary. Geology being the subject

of great depths and long ages (in million years), it is a unique interdisciplinary branch for

broad regional vision and to deliver long term solutions. A student of geology needs to be

aware of the independent importance of ‘Urban Geology’ rather than providing consultancy

to engineers and planners over small components demanded by them. It is, therefore,

necessary to include the urban geology in syllabus and the faculty needs to be trained. This

article is an introductory attempt to explore the scope of the subject to decide upon possible

guidelines in the study of urban geology.

Dr. Satish J. Sangode, with his basic interest in sediment magnetism, initiated his research carrier at Indian Institute of Geomagnetism, Mumbai during 1990. He joined Wadia Institute of Himalayan Geology during 1991 and developed a laboratory for Palaeomagnetism and Environmental Magnetism. Subsequently he established advanced environmental magnetic facilities at WIHG and initiated more work on Quaternary sediments (e.g., Sambhar lake, Ganga basin, Himalayan lakes, Delhi soils) as an independent attempt. Overall his work signifies the application of rock magnetism to hydrodynamics, paleo-environments and strain analysis towards more applied aspects of flood dynamics, neotectonic deformation and Quaternary climates. Prof. Sangode was awarded by prestigious the National Mineral Award-2005 in recognition to his work.

During late 2006 Dr. Sangode joined as faculty at the Department of Geology, University of Pune. Besides teaching, he continued his interest with integrated approach of environmental magnetism and geochemistry on the little understood but extensive palaeosol profiles in the Himalayan foreland basin as a long duration paleoclimatic record, anthropogenic loading of urban soils. He started teaching the courses on Indian Stratigraphy, Tectonics and Physics of the earth. In addition, at the Department of Geology he introduced a new two course ‘Quaternary Geology and Climate Change’. He explored new problems with field visits in coastal areas, Godavari and the urban soils of Pune and Mumbai metropolitan regions. Prof. Sangode published about 65 papers in national and international journals.