Impact of urbanization of regi lalma housing scheme on future floods in downstream creek
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Impact of urbanization of regi lalma housing scheme on future floods in downstream creek Impact of urbanization of regi lalma housing scheme on future floods in downstream creek Document Transcript

  • 1 EFFECT OF REGI LALMA HOUSING SCHEME ON FUTURE FLOODS Author Mohamed Reg:08PWAGR0584 Bakhta noor Reg:08PWAGR0582 Supervisor Dr. Muhammad Ibrahim DEPARTMENT OF AGRICULTRUAL ENGINEERING UNIVERSITY OF ENGINEERING AND TECHNOLOGY PESHAWAR 2011-2012
  • 2 EFFECT OF REGI LALMA HOUSING SCHEME ON FUTURE FLOODS This Project Thesis is submitted in partial fulfillment of the requirements for award of the degree of the degree of Bachelor of Science In Agricultural Engineering DEPARTMENT OF AGRICULTURAL ENGINEERING UNIVERSITY OF ENGINEERING AND TECHNOLOGY PESHAWAR, PAKISTAN
  • 3 SESSION: 2011-2012 EFFECT OF REGI LALMA HOUSING SCHEME ON FUTURE FLOODS A thesis submitted in partial fulfillment of the requirement for the award of degree of B.Sc. in Agricultural Engineering. Submitted By Bakhta Noor Mohamed 08PWAGR0582 08PWAGR0584 Supervised by Dr. Muhammad Ibrahim Department of Agricultural Engineering External Examiner’s Signature: ________________________________________ Thesis Supervisor’s Signature: ________________________________________ (Dr. Muhammad Ibrahim) Chairman’s Signature: ________________________________________ (Prof. Dr. Taj Ali Khan) DEPARTMENT OF AGRICULTURAL ENGINEERING UNIVERSITY OF ENGINEERING AND TECHNOLOGY PESHAWAR, PAKISTAN SESSION: 2011-2012
  • 4 Abstract The aim of this project is to determine the effect of proposed development of Regi Lalma Housing Scheme (RLHS) on future floods. During the proposed development the permeable soil is converted into impermeable soil cover such as roads, parking lots, pavements and roof tops. To estimate the discharges before and after proposed development we have three methods, Anderson method, Snyder method and Regression method. From the study and the results obtained from the three different methods. It is concluded the urbanization is the cause of the flood. The discharge before the development by any of the above three method is less than the discharge after the development. Due to this it is believed that urbanization is the cause of the flood. Flood cause severe problems. It destroyed fertile land, crops, buildings, roads, houses, aquatic habitat, pollute water, cause epidemic diseases, affect large number of people and most important cause the loss of precious lives. Hence it is necessary to take such steps during development to eliminate or reduce the impact of flood.
  • 5 ACKNOWLEDGEMENT Firstly, all praise is due to almighty ALLAH who bestowed upon us health and opportunity to successfully complete our B.Sc thesis. Countless salutation is upon the holy prophet Hazrat Muhammad (peace be upon him), the most perfect and a torch of guidance and knowledge for humanity as a whole. We would like to express our deepest gratitude and would like to gratefully acknowledge the enthusiastic supervision of Dr.Muhammad Ibrahim our esteemed promoter during this work, which has supported us throughout our work with his patience and knowledge whilst allowing us the room to work in our own way. His steadfast encouragement, guidance, support, kind concern and consideration from the initial to the final level enabled us to develop an understanding of the subject. He has been our inspiration as we hurdled all the obstacles in the completion of this research work. We are also thankful to our chairman Prof. Dr. Taj Ali Khan, department of agricultural engineering, for developing our mental level to an extent to tackle any kind of hurdles. It would be injustice if we do not endorse the continuous support of Engr. Khurram Sheraz (lecturer Agri Deptt) and Engr, Muhammad Ajmal (lecturer Agri Deptt) who despite the distance painstakingly guided us. Las, but not least, we warmly thank our parents for their financial and spiritual support in all aspects of our life, and who pray for our success, ceaselessly, without which we would certainly have not been able to achieve our goals.
  • 6 LIST OF FIGURES Number Page No. Figure 1.1 Effect of urban development on flood………………………………..2 Figure 1.2 Hydrograph before and after development of Mercer Creek, western Washington USA……………………………………………………...4 Figure 2.1 Increased runoff peaks and volumes increase stream flows………….7 Figure 2.2 Dubai in (1990) before development and (2007) after development….8 Figure 2.3 Wet pond……………………………………………………………..10 Figure 2.4 Storm water Wetland………………………………………………...11 Figure 2.5 Dry pond……………………………………………………………..12 Figure 2.6 Photograph of constructed infiltration basin at the Pony Express Car Wash in Oak Park Heights…………………………………………...12 Figure 2.7 Vegetated filter strip photo by University of Illinois Extension……..13 Figure 2.8 Photograph of grassed swale east of CR 13, Lake Elmo Dental Clinic…………………………………………………………………14
  • 7 LIST OF TABLES Number Page No. Table 3.1: Calculated data for Anderson method………………………………..22 Table 3.2: Anderson Time lag computation……………………………………..22 Table 3.3: Anderson flood frequency ratio……………………………………...24 Table 3.4: Calculated data for Snyder method…………………………………..27 Table 3.5: Ct values for Snyder method…………………………………………27 Table 3.6: Discharge estimation for Snyder method before development………29 Table 3.7: Discharge estimation for Snyder method after development………...30 Table 3.8: Proposed condition for BDF…………………………………………31 Table 3.9: Results of estimated discharges of different methods………………..32 Table 4.1: Results of estimated discharges before and after development…………..33
  • 8 TABLE OF CONTENTS Abstract……………………………………………………………………………….. i Acknowledgement…………………………………………………………………… ii List of figures………………………………………………………………………... iii List of tables………………………………… ……………………………………….iv Chapter 1: Introduction…………………………………………………………... 1 1.1: Background………………… ………………………………...1 1.1.1: Effect of urban development on floods…… ………….2 1.1.2: Hydrologic effect of urban development… …………..2 1.2: Statement of Problem………………………………………….4 1.3: Objectives……………………………………………………. 5 1.4: Scope of the study……………………………………………. 5 Chapter 2: Literature review………………………… …………………………...6 2.1: Flood……………………………….. ………………………...6 2.2: Types of flood……………... …………………………………6 2.2.1: Urban flooding…………….......................................... 6 2.2.2: Changes to stream flow………………………………. 6 2.3: Urban storm water management……………………………... 8 2.4: Storm water management system……………………………. 8 2.4.1: Lot-level and conveyance controls………………… 9 2.4.2: Soak way pits/Infiltration trenches………………….9
  • 9 2.4.3: End-of-pipe controls………………………………... 10 2.4.3.1: Wet ponds……. ……………………10 2.4.3.2: Wetlands……………. ………………11 2.4.3.3; Dry ponds…………………………… 11 2.4.3.4: Infiltration basin… …………………..12 2.4.3.5: Filters………………… ……………..13 2.4.3.6: Vegetated filter strips……………….. 13 2.4.3.7: Grassed swales…….. ………………..13 2.5: Important of storm water management……… ……………………...14 2.6: History………………………………………………………………. 15 2.7: Discharge measurement methods………………. …………………..16 2.7.1: Anderson method………………….. ………………………..16 2.7.2: Snyder method………………………. ……………………...17 2.7.3: Regression method…………… ……………………………18 Chapter 3: Materials and methods……………… …………………………………..20 3.1: Site…………………………… ……………………………………..20 3.2: Research parameters………………………. ………………………..20 3.2.1: Catchment area……………………………………………… 20 3.2.2: Impervious surface……………… …………………………..20 3.2.3: Time lag……………………… ……………………………..20 3.2.4: Time of concentration……………………………………… 21
  • 10 3.2.5: Length of main stream……………………………………… 21 3.2.6: Slope…………. ……………………………………………..21 3.3: Methodology…………………………………………………………21 3.3.1: Anderson method…………………………………………… 21 3.3.2: Snyder method…………………. …………………………...26 3.3.3: Regression method…………………………………………..31 Chapter 4: Results and discussion………. ……………………………………...33 Chapter 5: Conclusion and recommendation…………………………………… 35 5.1: Conclusion………………… ………………………………………..35 5.2: Recommendation…………….. ……………………………………..35 5.2.1: Storage controls……………… ……………………………..35 5.2.2: Infiltration controls…………………. ……………………....35 5.2.3: End-of-pipe controls……………………… ………………...36 References…………………………… ……………………………………………...37 Appendix ………………………………….. ………………………………………..39
  • 11 Google earth picture of the Regi Lalma Catchment area of the Takhta Beg Khawar near the Regi Lalma
  • 12 CHAPTER 1 INTRODUCTION 1.1 Back ground Urbanization is the process by which large numbers of people become permanently concentrated in small areas forming cities. The definition of a city or an urban area changes from time to time and place to place. The United Nations Organization has recommended that member countries regard all places with more than 20,000 inhabitants living close together as urban. Floods risk thought out the World in the past was not as high as today or will be in future. The reasons are that Urbanization was not at the alarming rate, the people were scattered in small’s villages and lived simple lives without so much infrastructures like buildings, roads, pavements and concrete houses. When rainfall occurred, some of the rainwater was infiltrated directly into the soil, some amount of the rainwater was stored in the watershed in the natural detention ditches and some fraction was absorbed by vegetation. The result was that the frequency and peak volume of the flood was less. The influence of humans on the physical and biological systems of the Earth’s surface is not a recent manifestation of modern societies; instead, it is ubiquitous throughout our history. As human populations have grown, so has their footprint, such that between 30 and 50 percent of the Earth’s surface has now been transformed. Most of this land area is not covered with pavement; indeed, less than 10 percent of this transformed surface is truly “urban”. However, urbanization causes extensive changes to the land surface beyond its immediate borders, particularly in ostensibly rural regions, through alterations by agriculture and forestry that support the urban population. Within the immediate boundaries of cities and suburbs, the changes to natural conditions and processes brought by urbanization are among the most radical of any human activity. [1]
  • 13 1.1.1 Effect of urban develop ment on floods The changes in land use associated with urban development affect flooding in many ways. Removing vegetation and soil, grading the land surface, and constructing drainage networks increase runoff to streams from rainfall and snowmelt. As a result, the peak discharge, volume, and frequency of floods increase in nearby streams. Changes to stream channels during urban development can limit their capacity to convey floodwaters. Roads and buildings constructed in flood-prone areas are exposed to increased flood hazards, including inundation and erosion, as new development continues. Information about stream flow and how it is affected by land use can help communities reduce their current and future vulnerability to floods. 1.1.2 Hydrologic effects of urban development Streams are fed by runoff from rainfall moving as overland or subsurface flow. Floods occur when large volumes of runoff flow quickly into streams and rivers. The peak discharge of a flood is influenced by many factors, including the intensity and duration of storms, the topography and geology of stream basins, vegetation, and the hydrologic conditions preceding storm events. Fig 1.1: Effects of Urban development on Flood
  • 14 Figure 1.1 illustrates how impervious cover and urban drainage systems increase runoff to creeks and rivers. The larger volume, velocity and duration of flow acts like sandpaper on stream banks, intensifying the erosion and sediment transport from the landscape and stream banks. This often causes channel erosion, clogged stream channels and habitat damage. [2] Land use and other human activities also influence the peak discharge of floods by modifying how rainfall and snowmelt are stored on and run off the land surface into streams. In undeveloped areas such as forests and grasslands, rainfall and snowmelt collect and are stored on vegetation, in the soil column, or in surface depressions. When this storage capacity is filled, runoff flows slowly through soil as subsurface flow. In contrast, urban areas, where much of the land surface is covered by roads, buildings and parking lots, have less capacity to store rainfall and snowmelt. Construction of roads and buildings often involves removing vegetation, soil, and depressions from the land surface. The permeable soil is replaced by impermeable surfaces such as roads, roofs, parking lots, and sidewalks that store little water, reduce infiltration of water into the ground, and accelerate runoff to ditches and streams. Even in suburban areas, where lawns and other permeable landscaping may be common, rainfall and snowmelt can saturate thin soils and produce overland flow, which runs off quickly. Dense networks of ditches and culverts in cities reduce the distance that runoff must travel overland or through subsurface flow paths to reach streams and rivers. Once water enters a drainage network, it flows faster than either overland or subsurface flow. With less storage capacity for water in urban basins and more rapid runoff, urban streams rise more quickly during storms and have higher peak discharge rates than do rural streams. In addition, the total volume of water discharged during a flood tends to be larger for urban streams than for rural streams. For example, stream flow in Mercer Creek, an urban stream in western Washington, increases earlier and more rapidly, has a higher peak discharge and volume during the storm on February 1, 2000, and decreases more rapidly than in Newaukum Creek, a nearby rural stream. As
  • 15 with any comparison between streams, the differences in stream flow cannot be attributed solely to land use, but may also reflect differences in geology, topography, basin size and shape, and storm patterns. [3] The hydrologic effects of urban development often are greatest in small stream basins where, prior to development, much of the precipitation falling on the basin would have become subsurface flow, recharging aquifers or discharging to the stream network further downstream. Moreover, urban development can completely transform the landscape in a small stream basin, unlike in larger river basins where areas with natural vegetation and soil are likely to be retained. Figure 1.2 illustrates that stream flow in Mercer Creek , an urban stream in western Washington, increases more quickly, reaches a higher peak discharge, and has a larger volume during a one-day storm on February 1, 2000, than stream flow in Newaukum Creek, a nearby rural stream. Stream flow during the following week, however, was greater in Newaukum Creek. Fig 1.2: Hydrograph before and after development of Mercer Creek, Western Washington USA. 1.2 Statement of Problem The aim of this study is to determine the impact of urbanization of Regi lalama Housing scheme on future flood in the Takhta Beg Khawar by estimating the
  • 16 peak discharge before and the proposed development of the Housing Scheme. The existing site of Regi lalma Housing Scheme (RLHS) consist of bar soil having high infiltration rate. The proposed development of RLHS will convert approximately 60% area of permeable soil to impermeable cover such as roads, parking lots and roof tops. It is believed that reduced infiltration after development will generate excess runoff and may overflow the Takhta Beg Khawar in future. Floods cause disasters such as water pollution, destruction of aquatic habitats, erosion of fertile lands, epidemic diseases, loss of precious properties, and loss of animals and at last the most important is the loss of human life. This shows that flood managements are necessary to control or at least minimize these losses. 1.3 Objectives  To determine the effect of proposed development of RLHS on future flood in Takhta Beg Khawar.  To recommend different options for managing the excess runoff thus generated by proposed development of RLHS. 1.4 Scope of the study: In Pakistan, the 2010 and 2011 floods were due to climatic changes according to the UN, but in 1996, Lahore city faced severe urban storm due to 500 mm rainfall in 24 hours. [4]. the flood caused severe problems. It has destroyed fertile land, crops, buildings, roads, houses, aquatic habitat, pollute the water, cause epidemic diseases, affect large number of people and also cause the loss of precious lives. It is necessary to discuss how urbanization causes the flood, so that we become able to take the necessary steps like Best Management Practices for storm water management to reduce the effect of urbanization on flood. It is hoped that the results of this study will produce a better understanding of urbanization and its effect on storm runoff. An attempt has been made to present the results of this study in such a way that it may be used to further advance the understanding of laymen. Hopefully planners will also be able to use the results to make better land use and development decisions.
  • 17 CHAPTER 2 LITERATURE REVIEW 2.1 Flood A flood is an excess of water on land that’s normally dry and is a situation where inundation is caused by high flow, or overflow of water in as established watercourse, such as a river, stream, or drainage ditch; or ponding of water at or near the point where the rain fell. A flood can strike anywhere without warning, it occurs when a large volume of rain falls within a short time. 2.2 Types of flooding  According to duration: Slow- Onset Flooding, Rapid-Onset Flooding, and Flash Flooding.  According to Location: Coastal Flooding, Arroyos Flooding, River Flooding and Urban Flooding. 2.2.1 Urban Flooding The Urban area is paved with roads, buildings, rooftops, parking lots, and pavements, and the discharge of heavy rainfall can’t absorbed into the ground due to drainage constraints leads to flooding of streets, underpasses and low laying areas.[5] 2.2.2 Changes to Stream Flow Urban development alters the hydrology of watersheds and streams by disrupting the natural water cycle. This results in:  Increased Runoff Volumes – Land surface changes can dramatically increase the total volume of runoff generated in a developed watershed as seen in Figure 2.1
  • 18  Increased Peak Runoff Discharges – Increased peak discharges for a developed watershed can be two to five times higher than those for an undisturbed watershed.  Greater Runoff Velocities – Impervious surfaces and compacted soils, as well as improvements to the drainage system such as storm drains, pipes and ditches, increase the speed at which rainfall runs off land surfaces within a watershed.  Timing – As runoff velocities increase, it takes less time for water to run off the land and reach a stream or other water body.  Increased Frequency of Bank full and Near Bank full Events – Increased runoff volumes and peak flows increase the frequency and duration of smaller bank full and near bank full events (see Figure 2.1) which are the primary channel forming events.  Increased Flooding – Increased runoff volumes and peaks also increase the frequency, duration and severity of out-of-bank flooding as shown in Figure 2.1 Lower Dry Weather Flows (Base flow) – Reduced infiltration of stormwater runoff causes streams to have less base flow during dry weather periods and reduces the amount of rainfall recharging groundwater aquifers.(GSMVol1– August 2001). Fig 2.1 Increased Runoff Peaks and Volumes Increase Stream Flows. [6]
  • 19 2.3 Urban Storm water Management Storm water management involves the control of surface runoff. The volume and rate of runoff both substantially increase as land development occurs. Construction of impervious surfaces, such as roofs, parking lots and roadways and the installation of storm sewer pipes which efficiently collect and discharge runoff, prevent the infiltration of rainfall into the soil. Management of storm water runoff is necessary to compensate for possible impacts of impervious surfaces such as decreased groundwater recharge, increased frequency of flooding, stream channel instability, concentration of flow on adjacent properties, and damage to transportation and utility infrastructure. [7] Fig 2.2: Dubai in (1990) before development and (2007) after development. [8] A storm water management control, measure or practice, such as a grassed swale or wet pond, is an individual element of a system. It may be a lot-level, conveyance, or end-of-pipe control. A practice may perform one or more functions, such as pretreatment or treatment, infiltration or storage for flood and erosion control. 2.4 Storm water management system A storm water management system or treatment train is a series of practices that meets storm water management objectives for an area. For example, rear yard soak away pits (a lot-level control), grassed swales (a conveyance control) and a wet pond (an end-of-pipe control) may comprise a treatment train. Unfortunately, the effects of urbanization cannot be mitigated through prevention alone. A storm water management “treatment train” is a series of practices
  • 20 that meets storm water management objectives for a given area. The “treatment train” approach combining lot-level, conveyance and end-of-pipe controls is required to meet the multiple objectives. Lot-level controls are those that are applied on individual lots (e.g. on residential properties) or for areas less than two hectares. The storm water runs off the lot into a ditch or a sewer which is part of the conveyance system. The conveyance system drains or conveys the runoff from the lots to an end- of pipe facility. End-of-pipe control facilities are those that receive storm water runoff from a conveyance system and discharge the treated water to receiving waters (usually a lake or stream). 2.4.1 Lot-level and Conveyance controls Most lot-level and conveyance controls may be classified either as storage controls or infiltration controls. Storage controls are designed to temporarily store storm water runoff and release it at a controlled rate. Although the volume of runoff does not decrease, the risk of flooding is reduced because all the storm water runoff does not arrive at the stream at the same time. The primary function of infiltration controls is to promote infiltration into the ground in order to maintain the natural hydrologic cycle. This can be best accomplished by lot-level infiltration controls because these can best recreate the pre- development conditions. Infiltration techniques can achieve water quality enhancement. However, these measures are ideally suited for the infiltration of relatively clean storm water including rooftop and foundation drainage. Storm water containing lots of sediment can plug infiltration controls unless the sediment is first removed. 2.4.2 Soak away Pits/ Infiltration Trenches Soak away pits and infiltration trenches are stone-filled (golf ball size) excavations where storm water runoff collects and then infiltrates into the ground. Infiltration trenches receive storm water from several lots in contrast to soak away pits which are used for individual lots. A filter layer at the base of the trench provides
  • 21 water quality enhancement of the storm water as it moves into the surrounding soils. There practices can only be used where soils allow the trench to empty within a reasonably short time. 2.4.3 End-of-Pipe Controls End-of-pipe facilities are usually required for flood and erosion control and water quality improvement, although lot-level and conveyance controls can reduce the size of the end-of-pipe facilities required. End-of pipe controls  Wet ponds  Wetlands  Dry ponds  Filters  Infiltration basins 2.4.3.1 Wet pond A wet pond is a detention basin designed to temporarily store collected stormwater runoff and release it at a controlled rate. It is different from a dry pond in that it maintains a permanent pool of water between storm events. Wet ponds are the most common end-of-pipe stormwater facility used in Ontarion. A single wet pond can provide water quality, erosion, and flooding control. Fig 2.3: Wet Pond ( Arika, Caleb and etall, Feb.2006)
  • 22 2.4.3.2Wetlands In contrast to wet ponds, constructed wetlands are dominated by shallow zones (less than 0.5). More vegetation can be incorporated into wetlands with the associated potential for water quality enhancement. However, because of their shallow depth, constructed wetlands are more land intensive than wet ponds and their application to flood control is limited. Fig 2.4: Stormwater Wetland [9] 2.4.3.3 Dry Ponds A dry pond is a detention basin designed to temporarily store collected stormwater runoff and release it at a controlled rate through an outlet. Dry ponds may have a deep pool of water in the sediment forebay to reduce scour and resuspension of sediment, but do not have a permanent pool of water in the main basin. This means that there is no opportunity for settling of contaminants between storm events and dilution of stormwater contaminants during storms. Therefore, although dry ponds can be effective for erosion and flood control, they do not perform as well as wet ponds for water quality control.
  • 23 Fig 2.5: Dry pond [10] 2.4.3.4 Infiltration Basins Infiltration basins may be needed in some situations to provide adequate groundwater recharge. However, water collected from a large area must infiltrate in a relatively small area. This does not replicate natural conditions as well as lot-level and conveyance infiltration controls. Infiltration basins can only be used where there are soils through which water can rapidly flow. They are ineffective for flood control because with larger water depths soil tends to be more compacted, allowing less infiltration. Pretreatment of stormwater is required to prevent groundwater contamination and clogging of soils. Fig 2.6: Photograph of Constructed Infiltration Basin at the Pony Express Car Wash in Oak Park Heights (Arika, Caleb and etall, Feb.2006)
  • 24 2.4.3.5 Filters Filters are stormwater management practice use for water quality control by filtering runoff through a bed of sand or other media. There are many types of filters. They may be at the surface or underground, and the filter media may be sand and/or organic material such as peat. Tilters can be incorporated into most parking lot areas and commercial sites. 2.4.3.6 Vegetated Filter Strips Vegetated filter strips (grass or forested) usually consist of a small dam and planted vegetation. The dam is constructed perpendicular to the direction of flow and ensures that the flow is spread evenly over the vegetation which filters out pollutants and promotes stormwater infiltration. Vegetated filter strips can be used as infiltration control, or a pretreatment control, and are best used adjacent to a buffer strip, watercourse, or drainage swale. Fig 2.7 Vegetated filter strip Photo by University of Illinois Extension. (Green, C.H, USDA-ARS) 2.4.3.7 Grassed Swales Grassed swales are typically shallow depressions several meters wide that convey stormwater. The vegetation slows and filters stormwater. Dams can be incorporated at intervals along swales to promote infiltration and settling of
  • 25 contaminants. Ditches and culverts (swales separated by culverts at driveways) may be used in residential areas as an effective alternative to curbs and gutters. (SMPD Manual, 2003) Fig 2.8: Photograph of grassed swale east of CR 13, Lake Elmo Dental clinic [11] 2.5 Important of Storm water Management. Storm water management prevents physical damage to persons and property from flooding, and also prevents polluted run-off from negatively impacting local waterways. The installation of impervious surfaces interrupts the natural hydrologic cycle, and causes less infiltration, interception, and evapotranspiration than was present before any development occurred. Therefore, the volume and rate of flow of storm water produced by the land surface have been greatly increased. The result of this larger amount of storm water runoff significantly contributes to flooding, sediment deposition, erosion, non-point source pollution and stream channel instability. Storm water should be considered a resource that provides benefits such as groundwater recharge, which maintains flows in streams. Storm water should be considered a resource that provides benefits such as groundwater recharge, which maintains flows in streams. Storm water management also reduces the frequency and severity of flooding. Traditional storm water management takes surface runoff and diverts it to a detention pond, which holds the water and releases it at a constant rate over time.
  • 26 This approach allows the water to be returned to the watercourse at a high volume over a longer period of time, which does not necessarily rectify the problem and may actually create another. If storm water is recharged into the groundwater, it can protect against erosion, flooding and water quality degradation. [12] 2.6 History Historically, stormwater management focused on the prevention of flooding and erosion in rivers and streams which receive stormwater. This reflected a societal view of river channels as conduits for the convenient passage of stormwater. In order to prevent flooding and erosion, agencies in urbanizing areas have taken drastic actions over long periods of time. These have included channelizing rivers and streams, building extensive flood protection works such as dams and energy dissipaters, creating large detention ponds, and construction ever-large storm drain systems to carry stormwater away from human- built impervious landscapes and into rivers. Unfortunately, such approaches to stormwater management have had a number of unintended side effects including the destruction of aquatic habitats, the diminishment of aquatic communities, the degradation of surface and groundwater quality, channel instability and the depletion of groundwater. Today, when designing stormwater management facilities, specialists recognize the importance of maintaining and enhancing surface and groundwater systems in a manner that as closely as possible resembles ‘natural’ form and function. Instead of conveying all stormwater into storm drains, designers consider facilities that allow infiltration of stormwater to recharge groundwater and maintain base flows of rivers. Instead of turning rivers into concrete channels to carry stormwater, designers are re-naturalizing channels to increase riparian cover and to create stable, self-maintaining forms. Instead of considering rivers as conduits of stormwater, designers are considering them as complex, self-regulating systems and important habitats for invertebrates, fish, birds, reptiles and amphibians. In short modern water resource management try to maintain healthy river systems. In such systems, a river’s energy is naturally dissipated through balanced rates of erosion and sediment
  • 27 transport. When erosion and sediment transport occur at natural rates, a variety of aquatic habitats are supported and channel morphology is preserved. [13] 2.7 Discharge measurement methods: 2.7.1 Anderson Method The Anderson Method was developed by the United States Geological Service (USGS) in 1968 to evaluate the effects of urban development on floods in Northern Virginia. Further discussion can be found in the publication “Effects of Urban Development on floods in Northern Virginia” by Daniel G. Anderson, U.S.G.S. Water Resources Division 1968. One of the advantages of the Anderson Method is that the lag time (T) can be easily calculated for drainage basins that fit the description for one of the three scenarios given: 1) Natural rural basin 2) Developed basin partly channeled or 3) Completely developed and sewered basin. For basins that are partly developed, there is no direct method provided to calculate lag time. The following explanation of lag time is reproduced from the original report to provide the user with information to properly assess lag time for use in the Anderson Method based upon the parameters used in the study. This method was developed from analysis of drainage basins in Northern Virginia with drainage area sizes up to 570 square miles. The equation for Anderson method is given as Q = R (230) × K × A . T . Where
  • 28 = Maximum rate of runoff (cfs) = Flood frequency ration K = Coefficient of imperviousness (obtained from equation 3.3) A = Catchment area (sq. mile) T = Time lag (hrs.) table 3.2 2.7.2 Snyder Method The Snyder Method was developed as the “Synthetic Flood Frequency Method” by Franklin F. Snyder. This was originally presented in the ASCE Processdings, Vol.84No.HYS in October 1958. The Snyder Method has been found to produce acceptable results when properly applied to drainage areas between 200 acres and 20 square miles. This method provides the user with an adjustment factor for partly developed basins by the use of percentage factors for the length of channel storm sewered and/ or improved. The equation for Snyder method is given as = 500AIR Where = Peak discharge (cfs) A = Catchment area (sq. Mile) IR = (in/hr.) = Time of concentration (hrs.)
  • 29 2.7.3 Regression Method Regional regression equations are a commonly accepted method for estimating peak flows at ungagged sites or sites with insufficient data. Also, they have been shown to be accurate, reliable, and easy to use as well as providing consistent findings when applied by different hydraulic engineers (Newton and Herrin, 1982). Regression studies are statistical practices used to develop runoff equations. These equations are used to relate such things are the peak flowor some other flood characteristics at a specified recurrence interval to the watershed’s physiographic, hydrologic and meteorologic characteristics. Rural regression method procedure is presented in the urban regression method procedure and the procedure of urban regression method is not intended to require measurement. A certain amount of subjectivity is involved, and field checking should be performed to obtain the best estimate. Then BDF is the sum of the four assigned codes, and the maximum value for a fully developed drainage system would be 12. Conversely, a totally undeveloped drainage system would receive a BDF of zero (0). In fact basin could be partially urbanized, have some impervious area, and have some improvement of secondary tributaries, and still have an assigned BFD of zero (0). The regression equation should be used routinely in design for drainage areas greater than one square mile. The equation of both the method are given bellow Rural regression method R = C Where R = Peak discharge for the rural watershed for recurrence interval T ( cfs) C = Regression contestant (dimension less)
  • 30 A = Contributing drainage area (sq. mille ) B = Regression exponent Urban regression method U = C (13 − ) R Where U = Peak discharge for the urban watershed for recurrence interval T (cfs) C = Regression constant (dimension less) A = Contributing drainage area (sq. mille) BDF = Basin Development Factor (dimension less) R = Peak discharge for an equivalent rural drainage basin in the same hydrologic area as the urban basin and for recurrence interval T, ( cfs) B1,b2,b3 = Regression exponents (Drainage Manual, April 2002). [14]
  • 31 CHAPTER 3 MATERIALS AND METHODS 3.1 Site The proposed RLHS is located on Nasir Bagh Road approximately 5 Km from Jamrud Road. The proposed Hosing Scheme spreads on 4054.2 ac and consists of 5 zones. After complete development approximately 60% pervious area will be converted to impervious area. The goal of this study is evaluate the effect of RLHS on future flood in Takhta Beg Khawar. 3.2 Research Parameters 3.2.1 Catchment area An area characterized by all direct runoff being conveyed to the same outlet is called catchment area. Similar terms include basin, sub watershed, drainage basin, watershed and catch basin. The catchment area of Takhta Beg Khawar at RLHS is 4104.4 ac provided by Peshawar Development Authority. 3.2.2 Impervious surface Impervious surfaces consist of roads, sidewalks, driveways, parking lots and roof tops. The estimated impervious area of proposed RLHS is 2524.20 ac which consist of roads, roof tops and sidewalks etc. 3.2.3 Time lag The time from the center of mass of excess rainfall to the hydrograph peak. Lag time is also referred to as basin lag. The estimated Time lag is calculated by formulas from table (3.2)
  • 32 3.2.4 Time of concentration The travel time from the hydraulically furthermost point in a watershed to the outlet. This is also defined as time from the end of rainfall excess to the recession curve inflection. The estimated Time of concentration is given by equation (3.9) 3.2.5 Length of main stream The length of longest stream from the start to the end of an outlet of catchment area is the Length of main stream. We calculated this with the help of ArcGIS. It is 5.0747 mile. 3.2.6 Slope It is the ratio of difference in Elevations at 85% and 10% (1341.86 − 1138.45)of the length of main stream to the difference in lengths at 85% and 10% (4.3135 − 0.50747) of length of main stream. We calculated these with the help of ArcGIS. The value is 53.44 ft/mile. 3.3 Methodology 3.3.1 Anderson method The equation for Anderson method is given as Q = R (230) K A0.82 T−0.48 (3.1) Where Q = Maximum rate of runoff (cfs) R = Flood frequency ration K = Coefficient of imperviousness (obtained from equation 3.3) A = Catchment area (sq. mile)
  • 33 T = Time lag (hrs.) table 3.2 Table: 3.1 calculated data Catchment Area 6.413 sq. mile Total Area of Regi. 4054.2059 acres Length of the main stream 5.075 mile Elev. At 10% of length 1138.45 ft. Elev. At 85% of length 1341.86 ft. 10% of length 0.50747 mile 85% of length 4.3135 mile Impervious Area of Regi. 2524.2059 acres Slope = ( . . ) ( ) (3.2) = ( . . ) ( . . = 53.44 ft. /mile Table: 3.2 Anderson Time Lag computations Time Lag, T Watershed Description 4.64 L √S . For Natural Rural Watershed 0.90 L √S . For Developed watershed partially channelized 0.56 L √S . For Completely Developed and Sewered Watershed
  • 34 Estimation of discharge before development T = 464 . (3.3) Where T = Time lag (hour) L = Length of the main stream (mile) S = Slope (ft./mile) T = 4.64 . √ . . = 3.98 hrs. Existing Impervious area = l = 4% K = 1+0.015×l (3.4) Where K = Coefficient of imperviousness l = percentage of imperviousness K = 1+ 0.015×4 K = 1.06
  • 35 Table: 3.3 Anderson Flood Frequency Ratios F 2.33 5 10 25 50 100 Rn 1.00 1.65 2.20 3.30 4.40 5.50 R100 1.00 1.24 1.45 1.80 2.00 2.20 = . × ( . × ) (3.5) Where Rf = Flood frequency ratio for flood frequency “f” based on percentages of imperviousness from 0 to 100% = . . × ( . × . . ) . = 2.129 = 2.129× (230) ×1.06× (6.413) . (3.98) . = 1228 cfs. = . . × ( . × . . ) . = 5.18868 = 5.18868× (230) × 1.06 × (6.413) . (3.98) . = 2991.83 cfs.
  • 36 Estimation of discharge after development Other parameters will remain unchanged only impervious area and Time lag will change after development. l = × 100 (3.6) = . . × 100 = 62.26 % T = 0.56 √ . (3.7) = 0.56 . √ . . = 0.463 hrs. K = 1 + 0.015 ×l = 1.934 = . × ( . × – ) = . × . ( . × ) . = 1 = R2 × (230) ×K×( ) . ( ) . = 1× (230) ×1.934×(6.413) . (0.463) .
  • 37 = 2954 cfs = . . × . ( . × . . ) . = 1.596 = 1.596× (230) ×1.934×(6.413) . (0.463) . = 4716 cfs = . . × . ×( . × . . ) . = 2.844 = 2.844 × (230) ×1.934 ×(6.413) . (0.463) . = 8403 cfs 3.3.2 Snyder Method The equation for Snyder method is given as = 500AIR (3.8) Where = Peak discharge (cfs) A = Catchment area (sq. Mile) IR = (in/hr.) Tc = Time of concentration (hrs.)
  • 38 Table 3.4: Calculated data Catchment Area 6.413 sq. mile Length of Main Stream 5.0747 mile Elev. At the Upper End 1391.076 ft. Elev. At the Down End 1122.047 ft. Ct = Adjustment factor defined by the development condition of the drainage area Table 3.5: Ct Values for the Snyder Method Type of Areas Ct, Hours/mile Natural Basins 1.7 Overland Flow 0.85 Sewered Areas 0.42 = × L (3.9) L = Equivalent length of channel with slope of 1% and friction factor equal to 0.1 and defined by the following equation L = × × √ (3.10) Where L = Length of main stream n = Roughness coefficient S = Weighted slope of the channel
  • 39 S = 39 (3.11) Mean height of elevation = . . (3.12) = . . = 134.51 S = 26.51 = 1% According to L description L = × . × . √ = 2.03 Discharge estimation before development Tc = Ct  L Where Tc = Time of concentration Ct = Adjusted factor L = Equivalent length. Tc = 1.7 × 2.03 = 3.451 hrs. Ct value is taken from the table which before development is Ct = 1.7 hr./mile From the rainfall data we use the 3.5 inches rainfall for 10-year discharge and 8 inches for the 100- year discharge. For runoff calculations for 10 and 100 –years discharge we use the graphs given in Appendix. Rainfall for 10-year return period = 88 mm = 3.5 inch
  • 40 Rainfall for 100-year return period = 204 mm = 8 inch From the graphs we have the following data The impervious area before the Regi lalma housing scheme is 4% Natural runoff for 10-year = 38% Natural runoff for 100-year = 64% Adjusted runoff for 10-year = 40% Adjusted runoff for 100-year = 64% Table 3.6: Discharges before development Frequency (years) 10-year 100-year Rainfall (inch) 3.5 inch 8 inch Percentage of Natural runoff (%) 38% 64% Percentage runoff adjusted (%) 0.4 0.64 Runoff (runoff adjusted × rainfall) 1.4 in/hr 5.12 in/hr Ir = runoff/Tc 0.406 1.484 Q = 500×A×(Ir) 1301 cfs 4758 cfs Discharge estimation after development Ct = it is selected from the table 3.6 Ct = 0.42
  • 41 Percentage of impervious area = = . ×100 = 62.26 % Tc = Ct × L = 0.42 × 2.03 = 0.853 hrs. Natural runoff for 10-year = 38 % Natural runoff for 100-year = 64 % Adjusted runoff for 10-year =75% Adjusted runoff for 100-year = 86% Table 3.7: Discharges after development Frequency (year) 10-year 100-year Rainfall (inch) 3.5 in 8 in Percentage of Natural runoff (%) 38% 64% Percentage runoff adjusted (%) 0.75 0.86 Runoff (runoff adjusted × rainfall) 2.625 6.88 Ir = (runoff/Tc) 3.079 in/hr 8.07 in/hr Q = 500× A × (Ir) 9873 cfs 25876 cfs
  • 42 3.3.3 Regression Method According to Rural Regression Method the discharge for the 10-year and 100- year is given below For 10 –year Q10 = 372 × . = 372× 6.413 . = 1287.241(cfs) For 100-year Q100 = 1254 × . = 1254 × 6.413 . = 3583.333 (cfs) Urban regression method After development Table 3.8: Proposed Condition of BDF Section A B C Storm drain 1 1 1 Channel improvement 0 0 1 Impervious channel lignin 0 1 1 Crub and gutter 0 1 1 Total of all 1 3 4 Total BDF 8
  • 43 For 10-year frequency Q10 = 9.51 × (1) . (13 − 8) . (1287.241) . = 2052.64 (cfs) For 100-year frequency Q100 = 7.7 × (1) . (13 − 8) . (3583.333) . = 4993.38 (cfs) Table 3.9 Result of different methods before and after development Methods Before development After development 10-years 100-years 10-years 100-years Anderson 1228 (cfs) 2991.83 (cfs) 4716 (cfs) 8403 (cfs) Snyder 1301 (cfs) 4758 (cfs) 9873 (cfs) 25876 (cfs) Regression 1287.241 (cfs) 3583.333 (cfs) 2052.64 (cfs) 4993.38 (cfs)
  • 44 CHAPTER 4 RESULTS AND DISCUSSION For our calculation we considering two conditions of Regi lalma, one is before the development as rural area and other after the development when complete development of Regi lalma housing scheme will occur as urban area. Table 4.1: Results of different methods before and after development Methods Before development After development 10-years 100-years 10-years 100-years Anderson 1228 (cfs) 2991.83 (cfs) 4716 (cfs) 8403 (cfs) Snyder 1301 (cfs) 4758 (cfs) 9873 (cfs) 25876 (cfs) Regression 1287.241 (cfs) 3583.333 (cfs) 2052.64 (cfs) 4993.38 (cfs) In every method either it is Anderson, Snyder or Regression the discharge after the development is grater then the discharge before the development. The reason is that Regi lalma was a rural area and mostly consist of bare soil, natural detention ditches, tress and grasses, so when there was rainfall most of the rainwater directly infiltrated into the soil, part of that rainfall water stored in the natural detention basin and some friction of rainwater absorbed by trees and grasses. The soil surface was rough and there was less chance for rainwater to accumulate quickly and cause peak discharge in nearby creek named Takhta Beg Khwar. The discharge after the development is greater because after completion of Regi lalma housing scheme the permeable soil will be replaced by the impermeable soil cover such as construction of roads, buildings, parking lots and pavements and due to which the infiltration rate of rainwater into the soil will be reduce, less water will be store on the soil surface due to elimination of natural detention ditches and no water will be absorb by the trees and grass due to deforestation. The water will accumulated on the soil surface causing larger volume of runoff water which will
  • 45 quickly join the nearby Takhta Beg Khwar. The drainage drains will reduce the time for the runoff water to reach the stream.
  • 46 CHAPTER 5 CONCLUSION AND RECOMMENDATION 5.1 Conclusion It concluded from this study that as the urbanization is increasing the risk of flood is also increasing, because with urbanization more and more permeable soil is converted into the impervious cover which infiltrate less water into the soil as a result the groundwater recharge is less and more water is accumulated on the surface which started runoff, the impervious surfaces and compacted soils, as well as improvements to the drainage system such as storm drains, pipes and ditches increase the velocity of runoff and reduce the Time of concentration causing peak discharge in the nearby stream and floods in the downside. 5.2 Recommendation Based on the results of this study. It is believed that urbanization of RLHS will increase peak discharge in Takhta Beg Khawar. Therefore the following control (mitigation) measures are recommended for RLHS. 5.2.3 Storage Controls  Rooftop storage  Parking lot storage  Super pipe (oversized storm sewer) storage  Rear yard storage 5.2.2 Infiltration controls  Reduced lot grading  Rear yard soakaway pits  Infiltration trenches
  • 47  Pervious pipe systems  Grassed swales  Vegetated filter strips 5.2.3 End-of-pipe Controls  Dry ponds  Wet ponds  Wetlands  Filters  Infiltration basins
  • 48 References: [1] Pollution, committee on reducing Storm water Discharge contributions to water. Urban Storm water Management in the United States. Washington, DC: The National Accedemic Press, 2008. -.Urban Storm water Management in the United States—2008, http://www.nap.edu.openbook.php?record_id=12465&=IR(Accessed June 22, 2012). [2] Ruby, Emily. “How Urbanization Affects the Water Cycle”. ---, California: -- RUPY EMILY,-- www.coastal.ca.gov/nps/watercyclefacts.pdf (accessed JUNE 22, 2012). [3] P. Konrad. Christopher.(USGS) “Effects of Urban Development on Floods”. pubs.usgs.gov/fs/fs07603/. [4] http://www.huffingtonpost.com/asif-iqbal/sustainable-cities-in-pak_b_1400446.html Accessed time 10:13 pm and date 6/26/2012 [5] http://www.unescap.org/idd/events/2009_EGM-DRR/SAARC-India-Shankar- Mahto-Urban-Flood-Mgt-Final.pdf . (9:35 pm) (22/6/2012) [6] Georgia storm water management manual volume 1: Stormwater Policy Guidebook First Edition – August 2001 [7] Stormwater Management Handbook by Pocono Northeast resource conservation and development Council. http://wren.palwv.org/products/documents/RCDStormwaterHandbook_000.pdf Accessed time (7:30 pm) and date (22/6/2012) [8] Farhad Abdolian in general middle east posted Feb. 18th 2008
  • 49 [9] www.dcr.virginia.gov/stormwater_management/documents/Chapter_3-09.pdf. Accessed time 5:56pm and 6/26/2012 [10] http://cfpub.epa.gov/npdes/images/menuofbmps/drypondpic.png Accessed time2:15 pm. And date 6/26/2012. [11] The storm management planning and design manual, 2003 is available on the ministry on environments (MOE) website at: http://www.enc.gov.on.ca. [12] Arika, caleb, Dario canelon, John Nieber, Feb. 2006, Impact of Alternative Storm water management Approaches on Highway Infrastructure: project Task Reports- volume 2. Published by Minnesota Department of Transportation Research Services section. http://www.lrrb.org/PDF/200549B.pdf [13] Storm water management guidelines, Our member municipalities may 1996.Credit Valley Conservation. http://mississauga.com/conservation.html [14] Drainage Manual prepared by location and design division hydraulics section April 2002 Virginia department of transportation.
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