 Namaste and welcome back to the video course on watershed management. Today, we will start a new module, module number 8 on stormwater and flood management. The topics covered in this module include stormwater management, design of drainage system, flood routing through channels and reservoir, flood control and reservoir operations and some case studies. So, in today's lecture in module number 8, lecture number 31, we will discuss stormwater management. So, some of the important topics covered in today's lecture includes stormwater runoff, harvesting, stormwater systems, integrated stormwater management, separate system, combined systems and urban flooding. So, keywords for today's lecture stormwater runoff system, harvesting, management and urban flooding. So, as we were discussing earlier, so when we deal with watershed management, so we have seen that there can be say sometimes plenty of water said due to heavy rainfall or sometimes there can be drought type situations. So, depending upon the climatic conditions or the variations say during monsoon season when heavy rainfall takes place, there can be say so much of water throughout the area whether it is say rural area or urban area. So, especially in urban areas when this water level goes up to certain say beyond certain level, there will be huge problems like say disturbance to the traffic, disturbance to the total life in that area and then a lot of there will be huge losses, economic losses. So, that means say the flooding, say urban flooding is a major problem say either in watershed scale or otherwise it is a major problem. So, this is caused due to the stormwater I mean due to the when the rainfall takes place as we have discussed earlier. So, we can classify into overland flow and channel flow. So, this overland flow component especially say this all this will be collected through drainage system various drains and then that will be joined into a stream or a channel and then finally, that will be routed through to the major river or to the ocean. So, that way only generally the system will be working. So, that way the stormwater management especially when during the rainy season or monsoon season the stormwater management within the watershed is an important topic. Since it is say in many aspects it is related to the say the problems that means like flooding problems or it is related to the water harvesting or whether we can capture some of this water and then recharge or do some harvesting. So, that way also it is important. So, in today's lecture let us discuss about the stormwater runoff, stormwater management and then urban flooding related issues. So, as I mentioned stormwater is a is rainwater and melted snow that runs of streets, lawns and other sides. So, that way say it is somewhat we can say it as a overland flow. So, whatever is say due to rainfall or due to melted snow say coming up through the lands and then coming to the streets and then lawns and other sides. So, this is generally timeless stormwater. So, when stormwater is absorbed into the ground. So, you can see that wherever infiltration takes place it is filtered and replenish the aquifers or flow into streams and rivers. So, whether it can be either this the stormwater can be re-chart to the aquifer systems through infiltration process or it can simply flow through the drainage systems to the streams and rivers. So, this is say both way it is possible, but we want as much as possible if it is say infiltrating down. So, that replenishes the aquifer system. So, that we can use say for future purpose. So, by pumping out the water from the aquifer systems. And then when we consider the urbanized watershed or urbanized areas say especially impervious areas like pavements and roofs prevent water from naturally soaking into the ground. So, you can see that in a city like Mumbai or Chennai or Calcutta or Delhi we can see that most of the areas say especially pavement and then so many some other lot of other areas are also say paved or it is impervious. So, that way this impervious surface say stops the water to percolate down to the to the ground. So, that way you can see that this water will be say moving fast. So, this water runs rapidly into storm drains or sewer systems and drainage ditches and then it can cause say lot of problems as we discussed. So, some of the important problems can be like say downstream flooding say if a huge heavy rainfall takes place and then all the this water the storm water is coming say to the areas downstream areas. So, then there can be possibility of flooding then stream bank erosion. So, say especially say wherever the soil is loose and then say heavy rainfall takes place there can be stream bank erosion and then wherever say especially this water will be going to rivers and then as it will be say many times this water will be taken back for say the say municipal water supply. So, then there can be increased turbidity. So, another issue can be increased turbidity and then habitat destruction changes in the stream flow hydrograph. So, that means say especially in the urban areas due to the time less time of concentration or time to peak will be less and then the peak also increases. So, that way there will be changes in the stream flow hydrographs and then there can be combined sewer overflows. So, wherever the sewage and then the storm water drains say single burn I mean combined system there is you can overflow and then it can create when especially mixed with sewage then there can be more problems environment problems and then infrastructure damage and then. So, this all this can cause contamination of the surface water like stream rivers, ponds or lakes and then also the coastal water bodies will be also affected by the polluted storm water. So, that way we have to manage the storm water very scientifically and then we have to we should appropriate plants and then appropriate drainage system and then say if we can treat this storm water to certain extent. So, that the surface water will not be or the or including the ground water will not be polluted due to the polluted storm water. So, that way we have to plan the system the storm water system appropriately. So, that way we can see that storm water management is very important topic when we discuss about the watershed management. So, now this whether we can harvest this storm water as we discussed we are discussing about the rain water harvesting earlier. So, now the question is whether we can capture the storm water which can cause other ways various problems like flooding or the pollution to the surface water bodies. So, if we can say harvest some of the water and then either we can use it or we can say infiltrate down to the aquifer systems. So, then that will be that will reduce the storm water problems like flooding. So, let us look say some important aspects related to storm water harvesting. So, storm water concerned for the volume and timing of runoff water. So, that means, flood control and water supplies and other related water pollution. So, storm water as we discussed it can cause flooding and then it can be also cause surface water pollution. So, that way a storm water say as I mentioned earlier it is also an important resource. So, since it is this storm water is not much polluted water if we give some simple treatment like sedimentation or like say settling dams through that kind of treatment we can directly utilize this storm water. So, storm water is say also resource which we can readily use for various purposes. So, say like techniques like storm water harvesting with the point source water management and purification can potentially make urban environment self-sustaining in terms of water. So, especially say urbanized watershed. So, we can see that when the urbanization increases more water is needed. So, that way water is available in that watershed may not be sufficient if especially if this storm water is not harvested or storm water is not properly utilized. So, that way if we can collect this storm water and then either allows this storm water to recharge to the to the aquifer systems or we can use to certain ways then that will be very useful. So, storm water harvesting is the collection, accumulation, treatment or purification and storing for its eventual reuse. So, storing can be either a direct storage like in a pond or in tanks or it can be also we can recharge to the to the ground water systems. So, that way the storm water harvesting is very important and it can also include other catchment areas from manmade surfaces such as roads or other urban environments such as parks, gardens and playing fields. So, that way in all these areas say we can capture the storm water and then say we can treat it properly purify it and directly utilize it or we can recharge to the aquifer systems. So, that way storm water harvesting is a very important in terms of appropriate water source utilization within a watershed. So, now let us look into various aspects of storm water management. So, as we have seen say especially in the rainy season say or monsoon season we have got so much of storm water depending upon the rainfall condition. So, say we have to deal with large quantity of water and then as we discussed there will be pollution problems also. So, we have to deal with the quality of the water. So, that way when we when we have to deal with the quantity and quality of the storm water we call the process as storm water management. So, generally say we have to go for the best management practices. So, which is best possible as far as the storm water management is concerned. So, the best management practice is often used to refer to both structural or engineer control devices and systems say like retention ponds or to treat polluted storm water say or say storage within a pond as well as operational or procedural practices. So, this storm water management is one of the best management practices. So, it can be for operational purpose or the procedural practices. So, there are many forms of storm water management and best management practices may include say manage the storm water to control flooding and erosion. Then manage and control hazardous materials to prevent release of pollutants to the environment such as source control say from an industry or other sources. Then plan and construct storm water systems so that condominiums are removed before they pollute the surface waters or the ground water resources. So, we have to when we look into the storm water management we have to deal two aspects one is the quantity of the storm water, second one is the quality of the storm water. So, quantity is concerned so that depends may depends upon the rainfall pattern the rainfall conditions. So, and then how effectively we can capture the storm water and then use for various purposes and then quality issues are concerned say from where the pollution is coming pollutant is coming and mixing with the storm water and then whether that will affect surface water sources like rivers, lakes or other say in surface water ponds and other things or it may this polluted water may infiltrate down to the aquifer systems and then also cause the pollution to the ground water system. So, that when we have to see that best management practices are followed as far as storm water management is consened. So, that way we have to occur and protect natural waterways where they still exist or can be rehabilitated. So, if it is say the development work is going on a natural say waterways areas then say how we can do best management practices. So, like we can build soft structures such as ponds, swaths or wetlands to work with the existing or hard drainage structures such as pipes and concrete channels. So, as far as storm water system, storm water management is concerned we can go for soft structures or we can go for hard drainage structures. So, soft structures generally in storm water management we call ponds, swaths or wetlands. So, that can appropriately collect the storm water and then so it will be automatically treated like a sedimentation and say treatment within a wetlands or we have to go for hard structures like we can collect all the storm water through pipes channels and then we can give appropriate treatment. Then we have to revise current storm water regulations to address comprehensive storm water needs. So, as far as say how we are effectively utilizing the storm water. So, depending upon that we can have appropriate rules and regulations as far as the storm water management is consened. And then we can enhance and enforce existing ordinances or laws to make sure property owners consider the effects of storm water before and after development of their land. So, all this depends say the whenever a water shed basis or a particular land device when we consider. So, it depends upon the developments taking place within that area. So, we have to we should have certain rules and regulations as far as storm water management is concerned. So that the private land owners or the property owners also say they also go through this laws and then implement this rules as far as the storm water is concerned. Then we have to educate a community about how its actions affect the water quality. So, most of the time as far as the private land owners or users they may not bother about the water quality related to storm water. But storm water say polluted storm water is a major cause of water pollution. So, that way we should have strict rules and regulations and then we have to implement these rules and regulations. So, that way we have to plan carefully to create solutions before problems becomes too great. Especially in cities like Mumbai or Delhi and other areas the urban storm water pollution is a major problems and then especially in places like Delhi where the groundwater is directly utilized back same from the aquifer systems. So, that way when this polluted water infiltrate down to the aquifer system the groundwater system will be also get polluted. So, that way we should be very careful to manage the storm water with respect to quantity and the quality. So, now let us look why we have to manage the storm water. So, as I mentioned in urbanized areas when urbanization progresses then the in various area also increases. So, that way that affects the storm water. So, that way as I mentioned the pollution problem one aspect and then the time of concentration and time to say the peak of the hydrograph will be increased with respect to natural watersheds natural watersheds. So, that way then some of the same problems like what can happen with respect to if you do not manage the storm water appropriately like a road flooding countries place and then related accidents washouts driver delays etcetera. And then other issues like a building and property flooding say some of the buildings may get collapsed or then property may be flooded and then there will be structural and property damage then same when this the storm water say if it is going through the sewer systems. So, then a sewer this water will come there will back up with space and that will be another environmental problem and then there can be problems like foundation settlements then a devalued properties etcetera. So, that way as far as water quality is concerned there will be major environmental damage then say many of the utilities will be affected. So, utility services interruptions like traffic interruptions or the internet or telephone lines can be cut or there can be related problems like that kind of interruptions can take place then increased clean up course. So, once say after the rainfall all these things are not done properly then many areas will be say lot of mud will be there lot of the solid waste will be on the road and other places. So, we have to spend more money for say clean up after the rainfall events and then related health hazards and then a person inconvenience then increased insurance cost. So, all these are all major issues related to storm water if you do not appropriately manage the storm water. So, some of the solutions can be as we discussed it can be soft solutions like ponds, swirls or say wetlands or we can have hard solutions like a congealed steel and SDP pipes and then congealed structures etcetera. So, where this what will be the storm water will be appropriately collected and stored and then treated and then released appropriately. So, that is why we have to go for storm water management. So, and then also say as we discussed depending upon the rainfall condition we have to manage a large amount of storm water to avoid flooding and other inconveniences and then a traditional storm water management design say earlier say general trend is we generally focus on collecting ender storm water in pipe networks like a storm water pipes and then we transport this storm water to say offsite and the as quickly as possible either directly and then we can either directly will be say disturbed to a stream or river say either with some treatment or without treatment and then to a larger storm water management facility for if it is treatment is there or they combined sewer system flowing to a wastewater treatment plant. So, that is where we have to say we have to effectively manage a storm water since the quantity may be higher and then the quality also we have to deal. And now in the say recent times say in countries like United States of America the same there is certain terms like as far as to deal with storm water related issues or urbanizing issues say a terms like low impact developments or LID and then wet weather green infrastructure. So, these terms are coming to picture in the last few years and these are say like as I mentioned there can be hard solutions as far as storm water management or soft solutions like appropriate land management with respect to the construction of ponds or waste same wetlands etcetera. So, this low impact developments and wet weather green infrastructure which these terms which are coming to say storm water management in the last few years this addresses the concerns through a variety of techniques including strategic site design and then measures to control sources of runoff and thoughtful landscape planning. So, the main emphasis in the low impact development or the wet weather green infrastructure is mainly see the landscape planning and then the main say emphasis on to treat the storm water wherever it occurs instead of carrying entire the storm water to some centralized location and then treat it and then discharge to a river. Instead of that we would like to deal with the storm water at a local level and it can be through landscape planning or it can be some storage in some ponds or say in some wetlands and then we have we should have appropriate plan. So, that way the terms like low impact developments and LID and then wet weather green infrastructure these techniques are now in developing stage in countries like United States and Europe and then Australia and so, these are found to be very effective to deal with the storm water related issues and then overall environmental improvement have been observed in many of the small cities wherever this LID and wet weather green infrastructure things are being implemented. So, that way the main emphasis on say we are going for integrated storm water management it is not simply collecting the under storm water and then treating, but we are looking to an integrated system where the storm water management is done by considering various aspects of the land use and then various other techniques. So, let us look into what is this integrated storm water management. So, integrated so, it is a actually integrated water management only of IWM of storm water. So, this address many of the issues affecting the health of waterways, water supply, challenges facing the modern urban city. So, that way when we are effectively utilizing the same the water at local level wherever the storm water is placed. So, actually we are reducing the water related problems since readily say we will be recharging the water or we will be storing at local level and that can be directly utilized. So, that way integrated water management of storm water known as low impact development in USA or water sensitive urban design WSUD in Australia. So, this integrated storm water management is known as LID in USA or WSUD in Australia. So, IWM has the potential to improve runoff quality, reduce the risk and impact of flooding and deliver an additional water resource to augment the portable supply. So, that the important times here are so, we want to reduce the risk and we want to say and reduce the flooding problem and then that will become a it will augment the water the portable water supply as far as the watershed is concerned. So, that way we are looking for development of modern city say and wherever the water needs will be made through these kinds of integrated water management. So, then altered runoff predicted by climate change has potential to increase the volume of storm water that can contribute to drainage and flooding related problems. So, that way we have to so, this integrated storm water management is a good option. So, we can reduce the problems like flooding or water quality issues and then also we can improve the availability of the water on a local level say in by side management or say land use, land cover management itself. So, that way this is this integrated storm water management is adopted in many countries nowadays. So, further this IWM offers several techniques like storm water harvesting as I as we have discussed that that reduce amount of water causing flooding then infiltration. So, infiltration means to restore the natural recharge of ground water and then bio filtration or bio retention. So, that means just like rain gardens to store and reach runoff and release it at a controlled rate to reduce impact on streams and wetlands treatments. So, that way the bio infiltration or bio retention is same through say by improving rain by making rain gardens or forest stations by improving the plan covering we can keep say the rain water for some more time and then it can be released in a controlled way. So, that the flooding will be reduced and then local water availability will be improved. So, that way the integrated water management in its infancy it is in infancy and brings together elements of drainage science, ecology and realization that traditional drainage solutions and transfer problems further downstream to the determinant of our environment and precious water resource. So, that way this integrated storm water management is very important as far as the environmental improvements then that means the water quality improvement and then also the water availability as far as the particular areas concerned. So, now let us have further discuss about some more aspects about this low impact development. Low impact development or LID aims to restore natural watershed functions through small scale treatments at the source of runoff as I already mentioned and the goal is to design a hydrologically functional sites that mimics pre development conditions. So, before the development what were the situations? So, we want to keep to certain extent to that level itself by controlled developments and then various other means. So, that way this LID say in LID land development mainly it is related land development and it works with nature to manage storm water as close to its source as possible. So, we do not want to take this entire storm water to some central locations and when treat it and then disturb to reverse, but local level we want to deal. So, that way it is land development issues and then LID principles the major principles are preserved and creates the natural landscape features and minimize the effective barbarousness to create functional and appealing sites drainage that treats storm water as source. So, this is the basic principle. So, we want to preserve and recreate natural landscape. Then some of the important practices as far as LID is concerned as I mentioned bioretention facilities, rain gardens, vegetative rooftops, rain barrels and permeable pavements. So, these are some of the practices which are adopted in countries like USA and then this LID say water is managed in a way that reduces impacts of built up areas and promotes natural water movement. So, that is the essence of LID. So, we are looking for natural water movement so that more recharge will be taking place and flooding will be reduced and then there will be less possibility of water contamination. And then say another time as far as the integrated storm water management is concerned green infrastructure. So, let us look into some more aspects of this LID and green infrastructure. So, as I mentioned LID restores a watersheds hydrological, ecological functions. So, as we discussed and LID is a sustainable storm water practice. So, that way the sustainability issues are there and that will be kept within the watershed and then environment improvement also taking place. And then green infrastructure generally refers to the systems and practices that use or mimic natural processes to infiltrate, evapotransferrate and then or reuse a storm water on the site where it is generated. So, that way by improving the vegetation cover or through various means within the area itself through green infrastructure we are say trying to say increase the evapotranspiration or evapotranspiration and then we are also trying to reuse the storm water say by infiltrating down to the ground. So, green infrastructure generally used at a wide range of landscape scales in place or in addition to more traditional storm water control elements to support the principles of say LID say which we discussed. So, then say the under time related to green infrastructure is wet weather green infrastructure. So, this encompasses the approaches and technologies to infiltrate, evapotranspray, capture and reuse the storm water to maintain or restore the natural hydrology. So, in all these LID or green infrastructure the major emphasis is on the keeping the natural ecology with minimal developments and then say give the possibility of recharge more recharge to the grounds or to the aquifer systems and then reduce the pollution. So, that way some of the benefits of LID and green infrastructure includes like benefits related to social, economic, environmental. So, social means it is a reduction in urban heat islands effects provide green jobs, green business opportunities. So, whenever this kinds of planning takes place there are more jobs are created and then education information provided through street kiosk then crime reduction, health benefits through walking, biking, running trails etcetera. So, there are some direct benefits and then some of the indirect benefits also and then economic benefits include energy cost reduction using wind powered lighting, then water conservation, then green enterprise business opportunities etcetera. Then as far as environment is concerned the total environment the improvement will takes place like carbon sequestration, improved water quality through 90 percent capture of storm water, then carbon footprint reduction recycling and beneficial use etcetera. So, these are some of the benefits of LID and the green infrastructure as part of the integrated storm water management. So, now say as we discussed so all these practices it is better to do on a watershed scale since watershed is the hydraulic unit as we were discussing in our lectures. So, when we are looking to storm water management on a watershed basis some of the important goals includes like a reduction of flood damage to life and property as we already discussed, then minimization of storm water and now from new developments, then reduction of soil erosion from construction activities, insurance of adiccate storm water facilities, then maintenance of ground water recharge, then prevention or reduction of non-bind storm water pollution, then maintenance of surface waters to ensure their biological functions, then protection of public health and welfare. So, like that number of goals we can set as far as the watershed based storm water management is concerned. So, depending upon the area depending upon the urbanization all it took place or how what place the urbanization taking place we can set our goals and then we can try to achieve these goals. So, the main goal will be to capture the storm water as much as possible quantity wise and then keep the best quality possible I mean to improve the water quality as far as the storm water is concerned. And some of the important principles which we adopt for watershed based storm water management includes same we can view the regulatory complaints as a minimum requirement for acceptance. So, wherever routes and regulations are there we have to see that they are implemented and then requires a storm water management plan considering watershed wide needs. So, when we consider the hydrology unit as watershed the watershed based management. So, then we have to see what are the other needs of the watershed. So, accordingly we can do the storm water management, then it also focuses on achieving good environmental results for the watershed in a cost effective manner. Then integrates storm water plans into projects, developments and project features then uses collaborative partnership to leverage and then deliver a combination of watershed improvements and then a coordinated mitigation or enhancement strategy. So, that way when we deal with watershed based storm water management we can with respect to the goals we can adopt specific technologies which meet with the regulatory compliance and then so that there will be improvement as far as the total environment on a watershed basis. So, that way when we look into the storm water management. So, let us now look into some of the important control structures measures. So, we can have various measures to deal with the storm water. So, that way let us look into various approaches as far as the storm water is concerned. So, the policies and source controls are concerned it can be public education, land use planning, material management etcetera. Then load level source controls are concerned then we can look for green roofs, local storage or detention, storm water harvesting, local infiltration etcetera. Then community level storm water control measures are concerned we can go for community infiltration facilities, storm water management ponds, constructed wetlands or natural wetlands. So, these are all same structural measures actually the policies and source control is concerned it is non-structural measures. Then watershed level measures it can be structural or non-structural depending upon what we are adopting or what kind of control measures we are going for. So, it can say the common approaches like manages water on a natural versus political boundaries, establishes water quality goals and say protects and then consider cumulative backs etcetera. So, we can go for various systems say depending upon what kind of category we are looking for or what kind of measures like whether we are going for structural measures or non-structural measures. So, various norms various approaches are possible. So, according to the our goal the set goals and specified principles and the complaints with respect to the regulations we can choose appropriate approach for that location or for that watershed like structural measures or non-structural measures and then we can go for the storm water management. So, this as far as storm water is concerned say you see that when we deal with the urbanized water sheds. So, say the most of the urbanized areas we will have the sewage system also we have deal with the sewage systems and then also we have to deal with the storm water. So, in many cities small or large cities there can be separate system one system for only to deal with the storm water and then another piping or other kinds of systems to deal with the sewage or the wastewater. So, that way we can have as far as storm water management is concerned we can have separate systems or we can some cities or some areas especially terrible countries we can see there can be combined systems. So, where both the the sewage systems or the wastewater and the storm water only one system is given that kind of system is for the combined system. So, let us look into some aspects of the separate system and combined system. So, in the separate system the polluted storm water runoff we transport through municipal separate storm sewer systems from which it is often discharged untreated to local water bodies and then to prevent harmful pollutants from being washed or dumped into water bodies we can also go for appropriate pollution control measures and separate systems are comprised of two independent piping systems one system for sanitary or the wastewater and another for the storm water systems. So, you can see here in this layout so, if this has some of the urbanized areas and then storm water is concerned it is now separately collected and then it is directly discharged to a river like this and then the wastewater is concerned it is all collected through the pipelines and there will be treatment facility like this and then after treatment it is discharged to the river or the stream. So, that is the basic principle of separate systems and now let us look into the combined system the combined sewer system conveys both the sanitary sewage and storm water in one piping systems. During normal dry weather conditions sanitary waste collected in the combined sewer system are diverted to the wastewater treatment planche and during the periods of significant rainfall the capacity of a combined sewer system may exceeded get exceeded let the that is so called excess flow. So, this is a mixture of so, storm water and sanitary waste and this directly discharged into large water bodies or sometimes say this excess flow we call it as combined sewer overflow. So, the system is like this so, say when there is no rainfall so, the under wastewater is collected and then it will be collected like this and then it will be treated at this location and then it will be discharged to the river or stream. And then say during the rainfall season there will be this sewage water or the sewage or the wastewater and the storm water will be coming and so, we can see a mixed combination of storm water and so, wastewater will be there and that will be discharged to the so, it may say depending upon the condition it may be treated or without treatment also sometimes it will be discharged to the streams or rivers. So, this is so called a combined systems so, that way what we are discussing is how to manage this storm water and then say whether it is say combined system or separate system so, that way we have to either we say collect through pipelines or the open drains and then it can be after treatment or without treatment it will be discharged. So, now, let us look into what are the effects of this say if you do not manage the storm water properly. So, as we discussed the main effect will be the flooding problem so, let us look into the urbanization effects and the flooding problem. So, say as we discussed whenever it be say urbanization takes place within a water shed so, many structures will be constructed roads will be constructed. So, the natural surface is covered by artificial structures so, that way it increases impervious areas and the channel characteristics of shape like shape, slope, roughness these are all better known as far as the urban areas are consensed and there will be changes in flow pattern and quality of unknown will be also influenced and then say the losses are concerned like infiltration losses we may we can sometimes we can neglect so, estimation of losses become simplified so, but this may lead to higher peak flow and then shorter time to peak and causes the flooding at the low lying areas and undesirable load to the downstream areas. So, you can see that if there is no urbanization the urbanization that means, natural water shed so, generally so, if you plot the hydrograph that means, time versus discharge you can see that say rural water shed where is not much urbanization it will be the hydrograph will be a flattened graph like this and the peak will be at this location. But if the same location if urbanization takes place then we can see that this hydrograph peak will be increased like this and then time to peak will be reduced so, that way we can see that what happens say the time of concentration is reduced. So, the time to peak is less and then huge quantity of water will be coming to the drainage systems over to the streams over to the river and then that will rise the water level water depth and then finally, the flooding will be the effect. So, the main urbanization effects will be like say the peak of the hydrograph or the discharge will be increased and then time to peak will be reduced so, that way there will be within a short duration there are possibility of flooding so, that is the main effect of urbanization. So, there can be this urbanization due to urbanization and then it is flooding urban flooding there can be number of reasons number of courses so, the some of the important courses are listed here so, the courses can be due to meteorological factors, hydrological factors or human factors so, the meteorological factors like rainfall, cyclonic storms, small scale storms, temperature, increase, snowfall and snowmage and then hydrological factors can be soil moisture level, groundwater conditions, infiltration, conveyor waste cover, channel conditions, tidal effects etcetera and then human factors like say changes in land use so, urbanization means actually what is happening is change in land use so, land use land cover changes then inappropriate drainage systems so, there is no effective drainage systems or the drainage system is not effective then occupation of flood plain areas so, like wherever the flood plain areas that is construct say buildings are constructed or it is engrossed then sudden in release of water from dams as due to the heavy rainfall conditions then climate change effects urban micro climate or indiscriminate waste disposal so, these are some of the the causes of urban flooding so, now say as we discussed say main issue is say the flood depth increases and time to peak is reduces so, that way sudden flooding can or flash flood can take place so, now let us look what are the problems related to urban flooding so, in this slide the impacts may include loss of money, temporary disruption to transportation systems or the telecommunication systems then inconvenience to city life and then it can also cause erosion and instability of soils on steeps, slopes, threatening houses so, there can be landslides and other related issues then the extreme events results in inundation for a prolonged duration then heavy rainfall, tidal influences and lack of adequate drainage system so, these are all some of the serious problems affecting the especially in coastal areas so, they say simultaneously with heavy rainfall in the tidal level also raises in a city like Mumbai then you can see that there will be heavy flooding problems and then that will be prolonged flooding as happened in 26 July 2005 so, due to the complexity of this problem so, say whenever we will deal with urban flooding or urban flood prediction we have to we need a sophisticated tools like geofoil information system and data we may have to get from remote sensing and then very complicated numerical methods like a final tunnel method or final difference techniques we have to utilize to see whether the flooding possibilities and other things so, urban flooding major issues are loss of life say economic laws then you know say disturbance to the transportation and the telecommunication systems and then also say the urbanization impacts say there can modification of say flooding characteristics say will be modified by introducing the storm drains in many of the urban areas then rapid removal of water from the drain area takes place as we discussed since the time of time and infiltration decreases and to delay the peak rate of runoff increasing and in the area of storage capacity and delaying outflow so, we can have the possibility of say detention pond so, that all this problem can be reduced and runoff from streets to drainage system takes place directly instead of through the drainage systems and flooding takes place since limited entire capacity of the drainage system and insufficient capacity of the say if it is pipe system so, insufficient capacity of the pipe drainage systems. So, to deal with say the urban flooding problems same we can say in urban hydrology there generally two types of approaches are used first one is empirical lumbered parameter approach. So, the empirical lumbered parameter approach so, we consider the end-day drainage areas in single units and then we estimate the flow at only at the most downstream point or the outlet of the watershed then we assume the rainfall is uniformly distributed in time and space over the end-day watershed and then we can have a technique like unit hydrograph for instantaneous unit hydrograph techniques and then we can see that how the system is behaving. So, other approach is called a physical process approach. So, in the physical process approach same we have to determine same or we have to go for appropriate design of this stormwater system we deduct the losses from the design storm to arrive at an excess rainfall rate how much is the excess rainfall taking place and then we can determine the flow to gutter or the drainage systems and then we can route through this gutter to the main channel and then same we can use say the we can route the flow through the principal conveyance systems and finally, we can determine the outflow hydrograph. So, accordingly the say depending upon the outflow hydrograph at the outlet or the watershed we can go for design or we can go for the management of the system which we consider. So, now what we are discussing is about the stormwater management and urban flooding related problems. So, when we deal with say the various measures say to delay. So, we can say we cannot completely control the storm runoff or we cannot totally say deal with the entire systems. So, we can generally we can reduce or delay these storm runoff. So, that number of measures are available like some of the say measures which we can utilize include large flat roofs, then porous parking lots, then increase recharge, then planting a high delaying grass, then increase forest cover, then detention basins, grassed waterways, porous sidewalks, then rooftop gardens, fountain storage etcetera. So, in all this what we are trying is say we are trying to delay the movement of the stormwater and then say we are trying to say infiltrate down some of the portion of this the storm runoff and then say the we are trying to delay the movements of the runoff. So, that say the time to peak will be increased and the peak also will be reduced as far as these urban storm runoff is concerned. So, before closing this lecture let us look into a case study later to the stormwater drainage for an urban area. So, the study area is a housing colony in Santa Cruz, Mumbai. So, here the aim is to study the actual situation of the flooding problem in a low lying urban area subjected to tidal effects and such as measures. So, presently the area is affected with the frequent flooding I mean say this study we have carried out in 2006. So, there were heavy flooding in 2005 itself. So, present status of the drainage system to submersible pumps which pumps this stormwater to outside drainage system and then there is a 900 mm diameter pipe say draining directly to a nearby river called a Mithi river. So, this is the area. So, you can see that here they say for this entire area there is a major drainage system going to the Mithi river here which will be joined to the to the Arabian sea and say here say the existing system was there was a drainage system which is joining here and then there was a 900 mm pipe which is taking all this stormwater from the area. But due to the heavy rainfall conditions say for example, in 2005 July 26 this entire area was flooded for few days and then the housing colony came to us to see the the remedial measures. So, here the two issues are there one is the main say flow taking place within the area and then also the tidal rise what is happening within this river system and then that will be the back flow coming to the to the area. So, when the water level rises in the river and high tide occurs the outfall of drainage subjected to tidal effects and consequence flooding. So, during the year 2004 a new 900 mm diameter pipe has been constructed, but in 2005 as I mentioned again there was flooding. So, here we analyze the system say hydrologically and then hydrologically also. So, our analysis showed that the stormwater discharge through the pumping is about 0.051 meter cube per second and the stormwater discharge through the 900 mm diameter pipe was 0.492 meter cube per second and total drainage that where the capacity is 0.543 meter cube per second. So, we used to here rational formula Q is equal to C I A and runoff coefficient has been considered as 1 and so accordingly we found that this say drainage system is effectively say useful only up to a rainfall of 25 mm per hour, but many times the rainfall exceeds many years the rainfall exceeds say it can be 50 mm per hour like that. So, during the monsoon as I mentioned river overflows and addition the heavier rainfall happens. So, simultaneously the reverse flow occurs and that is the main issue here. So, the problem in selecting the design criteria like unavailability of adequate natural slope to facilitate gravity flow and tidal effects encountered at the exit point and lack of space to provide appropriate drainage system. So, these were some of the problems in this area. So, then we analyze the hydrologically and hydrologically. So, various rainfall conditions like 25 mm per hour, 50 mm per hour, 100 mm per hour. So, like say like a 2 year return period, say 5 year return period, then say 10 year return periods like that up to 50 years return period like 100 mm per hour and then this shows the measure rainfall intensity and this shows the storm water discharge. So, and then we say did the hydraulic analysis using the Manning's equations q is equal to a into r to the power 2 by 3 s to the power 1 by 2 by n, where n is the Manning's reference coefficient, a is the drainage sectional area r is say hydraulic radius a by p, p is the vector perimeter, s is the slope. So, there we use this hydraulic analysis to suit say for example, at least 50 mm per hour if the rainfall intensity space how we can affect you design. So, that way what we identified through this study is the present existing ground level has to be increased at least a 60 centimeter in the lower levels of the low lying area. So, that advocates slope is available, then a small gutter all along the internal road of the area leading to the lowest point should be given. Since the existing 900 mm pipe is almost at ground level, it is advisable not to have cross connection to this. The entry of storm water from the surrounding areas needs to be prevented, then the cross section cross connection to the nearby draining nulla has to be cut off. So, these were some of the recommendations as far as the this study areas concerned. So, that way we did the hydraulic analysis hydraulic analysis and then we come up with certain recommendations to reduce the urban flooding problem in this area due to the storm water. So, before closing some of the questions like tutorial questions critically study the storm water management issues in India, what are the major problems in implementing appropriate storm water management systems in Indian cities like Mumbai and Calcutta and then you can compare with what is the systems in USA or UK and then come up with a better proposal for Indian storm water management city for Indian cities. Then some few self evaluation questions discuss storm water runoff parameters influencing on watershed basis. What is the best management practices related to storm water management? Discuss the integrated storm water management practices. What are the goals and principles of watershed based storm water management? Differentiate between separate and combined storm water management systems. Then what are the important measures for delaying storm water storm runoff? So, few assignment questions illustrates various storm water harvesting techniques. Why we have to manage storm water? Discuss the features of low impact development and green infrastructure within the perspective of storm water management. Illustrate important storm water control measures. What are the important effects of urbanization on runoff? Discuss the important causes of urban flooding. Differentiate between empirical lumbered parameter approach and physical process approach in urban hydrology. All these questions you can answer by going through today's lecture. So, before closing down one unsolved problem, what are the important storm water management problems in your watershed area? Collect the necessary data for the storm water design in your area with the help of rainfall data, topo sheets and other maps such as drainage network maps, land use land cover map, road network design and effective storm water management plan for your study area. So, as presented in the case study you can solve say for your study area you can come up with a typical design to deal with the storm water management issues. So, today what we discussed is storm water management. So, in the next lecture we will be discussing about the drainage design and related issues as far as say the storm water system is concerned. Thank you.