Frequent Floods in Bangalore: Causes and Remedial Measures
Abstract and Figures
Floods in an urbanised landscape refer to the partial or complete inundation from the rapid accumulation or run-off resulting in the damage to property and loss of biotic elements (including humans). Urban flooding is a consequence of increased impermeable catchments resulting in higher catchment yield in a shorter duration and flood peaks sometimes reach up to three times. Thus, flooding occurs quickly due to faster flow times (in a matter of minutes). Causal factors include combinations of loss of pervious area in urbanising landscapes, inadequate drainage systems, blockade due to indiscriminate disposal of solid waste and building debris, encroachment of storm water drains, loss of inter connectivity among lakes, housing in floodplains and natural drainage and loss of natural flood-storages sites. Flood mitigation in urban landscape entails integrated ecological approaches combining the watershed land-use planning with the regional development planning. This includes engineering measures and flood preparedness with the understanding of ecological and hydrological functions of the landscape.
Bangalore is experiencing unprecedented urbanisation and sprawl in recent times due to concentrated developmental activities with impetus on industrialisation for the economic development of the region. This concentrated growth has resulted in the increase in population and consequent pressure on infrastructure, natural resources and ultimately giving rise to a plethora of serious challenges such as climate change, enhanced green-house gases emissions, lack of appropriate infrastructure, traffic congestion, and lack of basic amenities (electricity, water, and sanitation) in many localities, etc. This study shows that there has been a growth of 1028% in urban areas of Greater Bangalore across 45 years (1973 to 2017). Urban heat island phenomenon is evident from large number of localities with higher local temperatures. The study unravels the pattern of growth in Greater Bangalore and its implication on local climate (an increase of ~2 to 2.5 ºC during the last decade) and also on the natural resources (88% decline in vegetation cover and 79% decline in water bodies), necessitating appropriate strategies for the sustainable management.
Frequent flooding (since 2000, even during normal rainfall) in Bangalore is a consequence of the increase in impervious area with the high-density urban development in the catchment and loss of wetlands and vegetation. This is coupled with narrowing and concretising storm water drains, lack of appropriate drainage maintenance works with the changes in enhanced run-offs, the encroachment and filling in the floodplain on the waterways, obstruction by the sewer pipes and manholes and relevant structures, deposits of building materials and solid wastes with subsequent blockage of the system and also flow restrictions from under capacity road crossings (bridge and culverts). The lack of planning and enforcement has resulted in significant narrowing of the waterways and filling in of the floodplain by illegal developments. Causal factors and remedial measures to mitigate impacts of flooding are:
Reasons
1. Loss of interconnectivity among lakes due to encroachment of drains or dumping of solid wastes, Construction and Demolition (C & D) wastes
2. Encroachment of flood plains and wetlands (construction in valley zones, flood plains and lake bed) and de-notifying lakes (under the guise of ‘dead lakes’ – no lake can be dead as it does the job of ground water recharge)
3. Narrowing and concretising storm water drains impairing hydrological functions of the natural drains
4. Loss of pervious areas - reduction of open spaces, wetlands and vegetation cover
5. Increased paved surfaces in the city (78% paved surface and likely to be 94% by 2020) due to unplanned irresponsible urbanisation by senseless decision makers.
Solutions: Ecological Management of Storm Water Drains and Wetlands to Mitigate Frequent Flooding in Bangalore
1. Reestablish interconnectivity among lakes by removing all blockades (encroachments, solid waste dumping)
2. Protect Valley zones and Buffer regions of wetlands: protect valley zones considering ecological function and these regions are ‘NO DEVELOPMENT ZONES’ as per CDP 2005, 2015
3. Stop narrowing and concretising natural drains
• Vegetation in the drain takes the load during peak monsoon, there is no need to concretise the channel.
• Vegetation allows groundwater recharge while treating the water (bioremediation);
• Drains with vegetation without any bottlenecks (hindrances) would be the best option to mitigate floods.
• Narrowing channel and concretizing would only increase the quantum of water and velocity, which would be disastrous.
• Objective should be towards mitigation of floods and not to generate high overland flows (with increased quantum and flow velocity)
• Experts should think sensibly with holistic knowledge (considering all subject knowledge) than fragmented narrow sectorial knowledge. Advice by pseudo experts would be detrimental as the society would be deprived of ground water, frequent floods and unnecessary livelihood threats.
4. Decongest Bangalore
• Shift major installations to other cities in Karnataka,
• Stop further industriaisation and commercial establishments in bangalore.
• Protect open spaces – lakes, parks, etc.
• Stop further growth of dying city – with water and oxygen scarcity
• BWSSB should stop issuing senselessly NOC (no objection certificate) to major building projects as there is not sufficient water in the city.
• Environment clearance as per the norms of Environment Protection Act (2016), Wetlands (Conservation and Management) Rules, 2016, SWM 2016, C & D Wastes, 2016, Air act 1981, Water (prevention of Pollution) Act, 1974.
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... The literature review provides their study on frequent floods in Bangalore and found that urbanization, particularly the loss of permeable surfaces, has increased floodprone areas. They recommended a different approach to flood mitigation, including better stormwater management, implementing green spaces, restoring natural drainage channels, promoting rainwater harvesting, and adopting sustainable urban planning to reduce flood risks Ramachandra et al. (2017) [1]. Mujumdar critically analyzes the role of unplanned urban development in affecting flood vulnerability. ...
... The literature review provides their study on frequent floods in Bangalore and found that urbanization, particularly the loss of permeable surfaces, has increased floodprone areas. They recommended a different approach to flood mitigation, including better stormwater management, implementing green spaces, restoring natural drainage channels, promoting rainwater harvesting, and adopting sustainable urban planning to reduce flood risks Ramachandra et al. (2017) [1]. Mujumdar critically analyzes the role of unplanned urban development in affecting flood vulnerability. ...
This study explores how the growth of cities and the loss of natural water feature, such as valleys, affect how rainwater flows, explicitly focusing on Bangalore, India. Research shows that rapid urban expansion, increased paved surfaces, and inadequate drainage systems significantly increase the risk of flooding. This work summarizes the findings of past studies on flooding in Bangalore, covering topics such as how changes in land use impact flooding, how computer models can be used to predict flooding, the benefits of using green spaces and natural features to manage rainwater, and the importance of involving the community in addressing flood issues. The review concludes by identifying areas where further research is needed, including using computer models to evaluate the impact of different urban development plans and the effectiveness of proposed solutions like restoring natural water features in reducing flood risk in Bangalore.
... Recently, Bengaluru encountered numerous flooding events in 2014, 2016, 2017 and 2020 [63,64]. The city floods even under normal rainfall circumstances due to growth in imperviousness, deterioration of wetlands and vegetation [65,66]. The massive rainfall events in the year 2017 have paralyzed some city sections [2]. ...
... The transportation-related indicators such as VKT, VHT, ASV, ATL, C_t, R_L, Veh are obtained from vajjarapu et al. [2] with the respective data. The data of water bodies density is obtained from Karnataka Lake Conservation & Development Authority [69], vegetation density and the concrete area is obtained from Ramachandra et al. [65,66]. The transportation-related indicator values are dependent on the policies and vary across different adaptation policy bundles. ...
The uncontrolled expansion of human-made structures is creating more impervious urban areas. These changes, coupled with extreme rainfalls and inadequate flood channelling infrastructure, lead to urban flooding. The urban transport sector is at constant risk from urban flooding, and it should adapt to these climate change effects. This study focuses on developing an indicator-based approach called composite adaptability index (CAI) to assess the urban transportation system’s adaptability to urban flooding based on exposure, susceptibility, and resilience. The weights of the indicators are estimated using Analytical Hierarchy Process (AHP), and the consistency tests are conducted to assess the efficiency of the weights. The index is tested on three adaptation policy bundles designed to improve the urban transportation system’s resiliency compared to the Business as usual scenario for the years 2030 and 2050 in Bangalore, India. Testing of CAI showed that all the adaptation bundles showed increased adaptability. Overall, bundle 1 gave the best CAI results with 0.662 and 0.660 for 2030 and 2050, respectively and a 2% gain from the BAU scenario.
... Recently, Bengaluru encountered numerous flooding events in 2014, 2016, 2017 and 2020 [63,64]. The city floods even under normal rainfall circumstances due to growth in imperviousness, deterioration of wetlands and vegetation [65,66]. The massive rainfall events in the year 2017 have paralyzed some city sections [2]. ...
... The transportation-related indicators such as VKT, VHT, ASV, ATL, C_t, R_L, Veh are obtained from vajjarapu et al. [2] with the respective data. The data of water bodies density is obtained from Karnataka Lake Conservation & Development Authority [69], vegetation density and the concrete area is obtained from Ramachandra et al. [65,66]. The transportation-related indicator values are dependent on the policies and vary across different adaptation policy bundles. ...
... Moreover, greenspace landuse saved N-choe from concretisation and safeguarded its soft bed and edges. Concretisation of channels increases streamflow velocity and poses a threat of downhill flooding (Ramachandra, Shivamurthy, & Aithal, 2017). Contrary to paved surroundings, green surroundings give room for channel flooding by allowing it to swell during heavy rains. ...
For long, the cities depended on grey infrastructure for draining stormwater. However, incidences of pluvial flooding are increasing, and existing grey infrastructure is unable to take up the additional stormwater load. Consequently, planners are forced to think of new and sustainable alternatives for stormwater management. Natural channels can supplement the stormwater drainage systems, but these channels in cities are reclaimed to provide land for housing and other functions despite their crucial role. This study presents the case of a natural channel in Chandigarh (India) that is redeveloped as a greenspace without compromising its function of stormwater conveyance. We analytically discussed the non-intentional preservation of this seasonal natural channel and introduced a new term, greenswales, for similar arrangements. A greenswale is defined as the stretch of greenspaces laid over a natural channel, ephemeral or intermittent, having stormwater detention and conveyance as primary functions during precipitation. This study's significant finding is that the seasonal natural channels in a city can be safeguarded through the judicious superimposition of green spaces over them. Crucial lessons from this case can guide new developments in utilising natural seasonal channels as a nature-based solution for stormwater management, reducing the load on grey infrastructure and providing the city with a greenspace.
... Bangalore Metropolitan Region is distributed into 384 Traffic Analysis Zones (TAZ) to model the transportation system. The road network and zonal map of BMR considered for this study are shown in Fig. 1 and Fig. 2. Since 2000, Bengaluru has been experiencing frequent flooding even under normal rainfall 3 conditions due to increase in impervious area, loss of wetlands and vegetation [44]. This coupled with the improper drainage system where the drains are under capacity and blockage of drainages due to solid wastes led to surface runoff [42]. ...
Globally, the response to climate change has been through mitigation to reduce the greenhouse gas emissions. But the inevitable climate change effects due to constant feeding of emissions into atmosphere leads to severe and extreme precipitation causing flooding. The combined impact of flooding, rapid urbanization and vehicular growth has become a looming threat to the transportation system which is affecting the developing economies disproportionately. There is an urgent need for the transport infrastructure to adapt to these climate change effects to reduce human as well as economic losses and adaptation is seen as the necessary tool to address this. In this paper, a methodological approach to formulate the adaptation strategies from urban transport to urban flooding in developing economies is presented. Further three adaptation policy bundles are formulated specifically to enhance the resilience of transportation system against urban flooding thereby strengthening the adaptive capacity of the system. These strategies are evaluated for the years 2030 and 2050 along with base year for various travel parameters to estimate the impact of flooding. This study finds that the implementation of bundle 1 is an effective adaptation measure when compared to bundle 2 and 3. The comparative analysis with BAU flooding scenario shows that VKT of bundle 1 is reduced by 4% and 3%, speeds increased by 21% and 45%, vehicle hours travelled by 9% and 8% for the years 2030 and 2050 respectively. Trips that are cancelled due to flooding can be nullified using appropriate strategies is also shown in this paper.
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Vegetation plays an important role in influencing the hydrodynamic behavior, ecological equilibrium and environmental characteristics of water bodies. Several previous models have been developed, to predict hydraulic conditions in vegetated rivers, but only few are actually used in practice. In This paper six analytic model derived for submerged vegetation are compared and evaluate: Klopstra et al. (1997); Stone and Shen (2002); Van velzen (2003); Baptist et al. (2007); Huthoff et al. (2007) and Yang and Choi (2010). The evaluation of the flow formulas is based on the comparison with experimental data from literature using the criteria of deviation. Most descriptors show a good performance for predicting the mean velocity for rigid vegetation. However, the flow formulas proposed by Klopstra et al. (1997) and Huthoff et al. (2007) show the best fit to experimental data. Only for experiments with law density, these models indicate an underestimation. Velocity predicted for flexible vegetation by the six models is less accurate than the prediction in the case of rigid vegetation.
This paper highlights some recent trends in vegetation hydrodynamics, focusing on conditions within channels and spanning spatial scales from individual blades, to canopies or vegetation patches, to the channel reach. At the blade scale, the boundary layer formed on the plant surface plays a role in controlling nutrient uptake. Flow resistance and light availability are also influenced by the reconfiguration of flexible blades. At the canopy scale, there are two flow regimes. For sparse canopies, the flow resembles a rough boundary layer. For dense canopies, the flow resembles a mixing layer. At the reach scale, flow resistance is more closely connected to the patch-scale vegetation distribution, described by the blockage factor, than to the geometry of individual plants. The impact of vegetation distribution on sediment movement is discussed, with attention being paid to methods for estimating bed stress within regions of vegetation. The key research challenges of the hydrodynamics of vegetated channels are highlighted.
Submerged aquatic vegetation affects flow, sediment and ecological processes within rivers. Quantifying these effects is key to effective river management. Despite a wealth of research into vegetated flows, the detailed flow characteristics around real plants in natural channels are still poorly understood. Here we present a new methodology for representing vegetation patches within computational fluid dynamics (CFD) models of vegetated channels. Vegetation is represented using a Mass Flux Scaling Algorithm (MFSA) and drag term within the Reynolds-Averaged Navier-Stokes Equations, which account for the mass and momentum effects of the vegetation respectively. The model is applied using three different grid resolutions (0.2, 0.1 & 0.05 m) using time-averaged solution methods and compared to field data. The results show that the model reproduces the complex spatial flow heterogeneity within the channel and that increasing the resolution leads to enhanced model accuracy. Future applications of the model to the prediction of channel roughness, sedimentation and key eco-hydraulic variables are presented, likely to be valuable for informing effective river management. This article is protected by copyright. All rights reserved.
Using hydraulic data collected in thirteen cross-sections in a 250 m long reach of Babolroud River, Iran, this study investigated the relation between flow resistance and vegetation in a gravel-bed river with vegetated banks. It was found that the maximum flow velocity occurred on the water surface for bare bank cross-sections, but near the vegetated banks the dip phenomenon was observed and the maximum velocity occurred below the water surface for vegetated cross-sections. The log law is valid at various distances from vegetated banks in gravel bed rivers with different commencement levels. The flow resistance was found to be an exponential function of the average relative roughness with the coefficient of determination 0.733. Correlation of coefficient of 0.943 was obtained by charting between relative velocity and nonlinear equation dependent on relative roughness, Reynolds number and plant inclination factor. More field investigations are needed to quantify and localization this relation.
Aquatic macrophytes are often the dominant factor influencing flow
conditions within the channels they occupy. Existing knowledge of how
stream plants affect the flow is outlined, and the different scales at
which vegetation resistance operates are proposed. Resistance is shown
to be a function of the size of the plants, their structural properties,
location in the channel, and the local flow conditions. Current models
to calculate this composite resistance effect are assessed in the light
of theoretical considerations of the nature of vegetation resistance.
New theory is also presented, which demonstrates the non-linear
relationship between channel resistance and the proportion of the
channel occupied by vegetation.
Flow resistance of natural grasses, sedges and willows was studied in a laboratory flume. The objective was to investigate, how type, density and placement of vegetation, flow depth and velocity influence friction losses. The plants were studied in various combinations under nonsubmerged and submerged conditions in a total of 350 test runs. The results show large variations in the friction factor, f, with depth of flow, velocity, Reynolds number, and vegetative density. The friction factor was dependent mostly on (1) the relative roughness in the case of grasses; (2) the flow velocity in the case of willows and sedges/grasses combined; and (3) the flow depth in the case of leafless willows on bare bottom soil. Leaves on willows seemed to double or even triple the friction factor compared to the leafless case despite the fact that the bottom was growing sedges in both cases. For the leafless willows, f appeared to increase with depth almost linearly and independently of velocity. Unexpectedly, different spacing of the same number of leafless willows with grasses did not have any significant effect on f. Based on the experimental work, a better understanding of flow resistance due to different combinations of natural stiff and flexible vegetation under nonsubmerged and submerged conditions was gained.
Experimental Investigation of Influence of Vegetation on Flow Turbulence
- N M Miyab
- H Afzalimehr
- V P Singh
Miyab, N. M., Afzalimehr, H., Singh, V. P., 2015, Experimental Investigation of Influence of
Vegetation on Flow Turbulence, International Journal of Hydraulic Engineering, 4(3), pp: 54 – 69,
DOI: 10.5923/j.ijhe.20150403.02
Frequent Floods in Bangalore: Causes and Remedial Measures
- T V Vinay
- S Bharath
- H Aithal
©Ramachandra T V, Vinay S, Bharath H. Aithal, 2017. Frequent Floods in Bangalore: Causes and Remedial Measures, ENVIS Technical Report 123,
Environmental Information System, CES, Indian Institute of Science, Bangalore 560012