MINISTRY OF EDUCATION AND TRAINING MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT THUY LOI UNIVERSITY LUU VAN QUAN THE RESEARCH ON DETERMINING OPTIMAL SIZE AND LAYOUT OF DETETION POND FOR THE MIXED URBAN AND AGRICULTURAL BASINS Major: Planning and management of water resources Code : 62-62-30-01 THE ABSTRACT OF DOCTORAL THESIS HANOI, 2015 The thesis was completed at the Thuy loi University Supervisors1: Assoc Prof Dr Tran Viet On Reviewer 01: Prof Dr Duong Thanh Luong Reviewer 02: Prof Dr.Tran Huu Uyen Reviewer 03: Dr Nguyen Van Tuan The thesis will be presented to the Doctoral Evaluation Council at Room 123-A1 buiding, Thuyloi University ………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………… Time of presentation: …………………… If you would like to get more information on this thesis, please feel free to visit: - The national Library - Thuyloi University Library INTRODUCTION The necessity of thesis In recent decades, due to the demands of the development, constructing the urban areas and industrial zones have shifted the soil structure of many agricultural regions to urban - agriculture mixed regions This change has increased flooding in these areas Using detention pond to regulate stormwater and reduce flooding is an effective solution However, there are no researches on the effects of detention pond to the construction cost of the drainage system for the mixed areas Thus, the theme: "The research on determining optimal size and layout of detention pond for the mixed urban and agricultural areas" very meaningful to reality and science Objectives Proposing a methodology to determine optimal size and layout of detention pond to reduce the construction cost of the drainage system for the mixed areas The scope of work and object of study The thesis focused on determining optimal size and layout of detention pond to reduce the construction cost of the drainage system for the mixed areas, applying to the Western Hanoi Object of study: the drainage system for the mixed areas, applying to the Western Hanoi The scope of work: - The optimal size and layout of detention pond to reduce the construction cost of the drainage system for the mixed areas in terms of ditermining topography, ground, slope of canal as well as location of constructions - Regardless of sewage or water quality as well as other costs such as operating costs and maintenance of drainage system - Applying to the western Hanoi Research methods and approaches 4.1 Approaches: Approaching the system, inheriting available researches 4.2 Research methods and used techniques Inherited methods, modeling and simulation methods, analysing system and optimization, statistical methods Scientific and practical significance Scientific Significance: The thesis provides scientific methodology for determining the optimal size and layout of detention pond to reduce the construction cost of the drainage system for the mixed areas Practical Signigicance: The thesis proposed the percentage of area and form of rationl layout of detention pond in the Western Hanoi This result can be applied in planning of detention pond for the Western Hanoi and other areas with similar conditions New contributions of the thesis This thesis provided a scientific method to determine the capacity and layout form of detention ponds for the mixed urban and agricultural drainage to reduce the construction cost The new method includes: constructing objective functions, identifying components of the objective function, solving optimization problems, suggesting a decision alternative (i.e instead of proposing and calculating each of available alternatives in detail, these alternatives were compared, and then the best alternative was selected) The new method overcomes a limitation of the existing method which limits quantity of alternatives, hence the new method is considered more appropriate than the old one The thesis has applied the new method successfully for a case study- a basin in Western Hanoi This area is currently being urbanized, and industrialized with the combination of agricultural land and urban land The thesis used SWMM5.0 (Storm Water Managament Model of EPA, USA) to analyze and evaluate 500 options including centralized detention ponds at the headworks or decentralized ponds at major channels and at minor channels The results show that: i) For this study area: The appropriate ratio of detention pond area to total drainage basin area fluctuates from 2% to 3.82% depending on two factors: (1) layout form of detention ponds (i.e decentralization or centralization) The more dispersive the detention ponds are, the higher the ratio is; (2) land acquisition cost The more the land acquisition cost is, the smaller the ratio is and vice versa; ii) With the same ratio, the more dispersive the detention ponds are, the less the land acquisition is and vice versa This result (first time) proved (through specific data) the effectiveness of the motto "spraying water, burying water" proposed long time ago by water resources experts of Viet Nam The research results can be applied for other similar drainage areas The layout of thesis There are three main chapters: Chapter Overview of detention pond, effect of detention pond to drainage system for the composite areas Chapter Methodology and research tools Chương Researching and determining the optimal size and layout of detention pond for the Western Hanoi CHAPTER OVERVIEW OF DETENTION POND, EFFECT OF DETENTION POND TO DRAINAGE SYSTEM FOR THE COMPOSITE AREAS 1.1 The function of detention pond 1.1.1 Terms The detention pond is a terminology standing for lowlands, valleys where have water storage capacity (temporary or permanent), formed in natural or artificial conditions The system is responsible to drain simultaneously for either agriculture and urban area called the drainage system for the mixed areas 1.1.2 The function of detention pond The detention ponds in drainage system simultaneously perform multiple functions such as regulating stormwater, reducing flood, storing water for irrigation, aquaculture, improving the microclimate, creating good ecological environment In this research, detention pond (called HDH) focuses only on the function of regulating stormwater and reducing flood 1.1.3 The connecting forms between detention pond and chanel There are two connecting forms: detention pond is on channel and detention pond is beside of channel (1) Pond on channel is construction connected from pond to channel by spillway, culvert or channel or combination between channel and spillway, channel and culvert (2) Pond beside channel is part of channel extended with function of regulating water 1.2 Overview of using detention pond 1.2.1 On the world Detention pond used to reduce flood in urban areas have built widely since 06’s of 20th century all around the world However, the uneven contribution of pond area with total drainage area is diffirently divieded among cities as well as continents 1.2.2 In the Vietnam The detention pond in urban drainage system have area ratio from 1% to 5%, most natural lakes, and scattered distribution Some detention ponds use less efficient due to the location, area ratio, capacity, operation or connecting system between pond and channel 1.3 Overview of researches on detention pond 1.3.1 On the world There have been many researches on the effect of detention pond to the flooding, environment and landscape Some studies which have figured out the approaching method by using detention pond to store the rainfall for other purposes is very effective either technique and economy Some studies shown that the concentrating pond reduce peak discharge and flooding better than dispersing pond 1.3.2 In the Vietnam Some studies on sustainable drainage have considered the detention pond under the aspect of dispersion, rainfall reducing at source (stored in households and increased permeability) The studies about the influence of the detention pond to the drainage headworks were also considered In addition, studies of other fields (environment, landscape, ecology) were also announced In conclusion, either worldwide and Vietnam doesn’t have any research on relationship between size and layout form of detention pond to the construction cost of the drainage system for the composite areas 1.4 Conclusions of chapter The results of research show that: 1) Area ratio of detention pond in cities on the world and in the Vietnam are very different 2) Most of the research focused on the function of environmental improvement and storing water for many different purposes 3) Concentrating pond has good efficiency for reducing the peak discharge, flooding area and the flooding depth depends on the scale and layout form of detention pond 4) Detention pond in agricultural drainage system have researched at the simple level: aquaculture pond, storage water in fields 5) Effect of detention pond to headworks is very clear There are no researches on relationship between size and layout form of detention pond to the construction cost of the drainage system for the composite areas According to above reasons, the thesis: “The research on determining the size and form of rational layout for the composite area” is sponsored to research CHAPTER METHODOLOGY AND RESEARCH TOOLS 2.1 The detention pond in the drainage system 2.1.1 The detention pond in the urban drainage system The detention pond is one of terms of urban drainage system The detention pond originated from either nature or artificiality is distributed in residential areas or park to store rainfall, reduce flooding, improve the environment and provide water for irrigation 2.1.2 The detention pond in agricultural drainage system The detention ponds in agricultural drainage systems are natural ponds or lakes existing before headworks were built The natural ponds are sparsely distributed and the artificial pond has function on aquaculture or irrigation These detention ponds have function to store rainfall, reduce the peak discharge for downstream constructions, and provide water for irrigation 2.1.3 The detention pond for composite areas The drainage system for composite area includes simultaneously drainage construction for urban areas and for agricultural areas Constructions in drainage system are characterized by incharge area is urban or agricultural 2.2 Making the problem to determine the size and layout of detention pond Figure 2.7 Drainage system layout for the composite areas The problem is applied to the composite areas The initial conditions of the problem stated that the drainage ground, land using and infrastructure need to be planned in the researching area (determing location of the drainage headworks, regulating culvert and canals) Therefore, the detention pond area may be reached to a certain rate Requirement: Determing the size and layout form of detention pond in order to minimize the construction investment cost and ensure no waterlogging corresponding the design storm 2.3 Method 2.3.1 Proposing the sequence to solve the problem a Traditional method It is based on experience, by calculating and direct comparision, the designers give out the best appropriate method The steps of solving will be shown in the figure 2.9 The advantage of this method is easy to implement and the disadvantage is that the calculation volume is too large and the result depends subjectively on the proposing person b New method The author proposes a new method to determine the size and form of rational layout for detention pond (Figure 2.8) including building objective function, solving the optimization problem by regression method, proposing a reasonable solution Studing basin characteristic: Studing basin characteristic: Topography, geology, land Topography, geology, land using… using… Proposing some solutions: (channel, detention pond) Proposing some different solutions: (canal, Determining the designing flow rate of each method Establishing methods (hydraulic, hydrological calculating – determining designing flow rate and method scale by modelling) Economy, technical calculating of each method Establishing regression function Comparing methods, determining the reasonable method Solving multi-objective optimization problem (using empirical planningmethods to solve) Proposing selected method Proposing selected method Figure 2.8 New method Figure 2.9 Traditional method (Diagram of determining steps of the reasonable layout of the detention pond) The basic advantage of this proposed method is to increase the considered cases (more than 500 cases), regardless of the experience of proposer Thus, the rationality of the proposed method is very high 2.3.2 Facility to determine the size and layout form of detention pond The construction area should take advantage of the natural ponds and farmland and are not coincided to the technical infrastructure already planned The calculating scenarios are created from the combination of size and layout form of the detention ponds (concentrated or dispersed) in the determined region under the plane containing thescale and layout form axis (Figure 2.10) Main  cannal KC  VT1 Branch _ 01 Branch _ 02 Branch _ i Branch _ m N 01  VT1 N 02  VT1 Ni  VT1 Nm  VT1 KB1 KC  VT2 N 01  VT2 N 02  VT2 Ni  VT2 Nm  VT2 KB  KC  VTn N 01  VTn N 02  VTn Ni  VTn Nm  VTn KB n Figure 2.10 The determining method of layout form scenario 2.3.3 Determining the size of the drainage system in scenarios After proposing the scenarios on size and layout of detention ponds, it is period to determine the construction scale in system by following steps: 1st Step: Determining the preliminary dimensions of channels, pumping stations according to the current regulations, namely follow to the formula in TCVN 7957: 2008, TCVN 4118-85 2nd Step: Using Storm Water Management Model 5.0 (SWMM 5.0, EPA USA), to simulate and to check the system determined from the 1st Step This problem suggests for the urban drainage system and appling “on-farm detention pond” method for the agricultural area The calculating result of on-farm detention pond method is outflows and they are entered into the SWMM 5.0 model as inflows at Nodes 2.3.4 Establishing the objective function and the constraint conditions a General objective function General objective function for reasonable design problem is only minimum the construction investment cost The general objective function form: m T  n  j j j C htj  C đm  C htk  C hdh    C đmi   Cthkj   C hdh   Min 1  j (2.25) According to the above relationships, the figure 2.26 has summersized the relationship between construction investment cost and pond area or pond’s area ratio In where: Cđm Construction investment cost in headwork, Chtk Construction investment cost for channel system, Chdh Construction investment cost for detention pond, Cht Construction investment cost for whole system Figure 2.26 The relationship form between construction investment cost and pond area 2.4 Conclusions of chapter Using experimental planning method to solve the problem to get the results of high accuracy The extreme points of construction investment cost that is minimum (reasonable method) depends on the construction unit prices and unit costs for site clearance compensation When compensation unit price is higher, the extreme points will close to the origin and when construction cost is higher, the extreme points tend to back away from the origin (Figure 2.26) The methodology also presents a problem description and resolution procedures With the method described, this methodology can be applied to all the basins where have the composite area The Storm Water Management Model 5.0 is selected to simulate the hydrology, hydraulics for urban area, on the other hand, the on-farm pond is selected to 11 resolve to the agricultural area Methods and tools described above are applied to specific research areas in the west of Hanoi CHAPTER RESEARCHING AND DETERMINING THE OPTIMAL SIZE AND LAYOUT OF DETENTION POND FOR THE WESTERN HANOI BASIN 3.1 Selecting and describing the research area 3.1.1 Selecting the research area The west of Hanoi is selected to be a case study for the problem of determining the size and form of detention pond The spindle is Nhue river from the Lien Mac culvert to the Ha Dong culvert The Dam river, Cau Nga river and La Khe river also are studied in the research The incharging area of drainage is 17,965 including 13,917 of urban planning, 2.090ha of greenbelts planning along Nhue river, 1,958 of agricultural land [68] The drainage system satisfied the data and boundary conditions, so it satisfy the requirements of the proposed problem in Chapter Picture 3.1 The study area in the West of Hanoi 12 3.1.2 Features of ponds and lakes in the study area The study area has flat topography; natural ponds are few in number and small in size The natural pond is not involved in regulating rainfall 3.2 Validation of the Storm Water Management Model 5.0 3.2.1 Purpose To ensure the reliability of the model, consistent with the research problem, using this parameter is to simulate the scenario of the research problem 3.2.2 Validation results Table 3.1: The evaluation table of the error of the calculating and measuring process Measuring station Daily rain Hà Đông 24/8 - Đồng Quan 28/8/2010 Max discharge (m3/s) Total discharge (m3) Measur Calcu Error Calculati Error Measuring ing lating (%) ng (%) Error S/ 81,58 82,78 1,48 8.052,9 8.076,72 0,70 0,15 105,66 107,16 1,42 10.365,7 10.739,8 3,61 0,18 From table 3.1, the indicators on the maximum discharge, the total discharge and the line form are achieved So it is possible to apply these simulations to test the model Table 3.2: The evaluation table on the error of calculating and measuring process (02 rains) Max discharge (m3/s) Measuring Station Hà Đông Đồng Quan Hà Đông Đồng Quan Daily rain Total discharge (m3) Error Measu ring Calcul ating Error Calculatin Measuring g (%) Error (%) S/ 22/5 - 89,60 93,92 4,82 8.819,67 8.773,56 0,52 0,08 26/5/2012 101,19 101,36 0,17 11.671,77 11.549,44 1,05 0,32 17/8 - 65,11 66,73 2,68 7.192,45 7.340,79 2,06 0,10 19/8/2012 100,61 99,08 -0,25 11.091,29 11.022,57 0,62 0,08 From table 3.2, the error of line form is from 0.08 to 0.32, the error of maximum discharge is from 0.17% to 4.82%, the error of total discharge is from 0.52% to 2.06% Thurs, the errors were smaller than allowance 13 Therefore, the calculating line and measuring line is well reasionable with each other The SWMM can be appied to calculate for this thesis 3.2.3 The model parameters were chosen after testing a The parameters of padded surface - Coefficient of surface roughness with hard coating: n = 0.025 – 0.15 - The parameters on the characteristics of soil permeability: Maximum permeable coefficient kmax = mm/h; kmin =0.5 mm/h, the saturated seapage time is days, average permeability is 25mm b The bed roughness coefficient: River and earth channel: n = 0.025 – 0.03; river and earth channel with embankment stone roof: n = 0.017 c Calculating time: t = 60 s 3.3 Establishing the specific objective function for the West basin of Hanoi 3.3.1 The general objective function The Chapter have determined the general objective function as following formula: n C = Cđm + Chtk + Chdh = C m T đmi   Cthkj   C hdh => Min 1 3.3.2.Determining the components of objective function The construction costs and the clearance price at the fourth quarter period in 2013 of the west of Hanoi to determine the components of the objective function By considering the impact of costs for site clearance to the selection of appropriate layout scripts, author has selected 03 cases of calculations, including: TH1 (100% of agricultural land), TH2 (85% of agricultural land and 15% residential land), TH3 (70% and 30% of agricultural land for residential land) a The drainage system headwork is pumping stations To determine the parameters in the objective function of Cđm ~ Qđm, this studying used the data of 21 pumping station in the west of Hanoi and vicinity area and updated to the cost estimates with unit price at the fourth quarter period in 2013 14 The regression function: TH1: Cdm = 1,6578*(Qdm)1,4532; (3.4) TH2: Cdm = 1,7064*(Qdm)1,4491; (3.5) TH3: Cdm = 1,7566*(Qdm)1,4451; (3.6) With, Cdm is construction investment cost in billion Dong, Qdm is the upstream discharge in m3/s Figure 3.18 Diagram showing the relationship of Cđm ~ Qđm b Drainage channel system * The regression relationship between discharge and construction investment cost of the channel grade 3: The channel grade usually structured as reinforce concrete round sewer or box sewer buried underground The regression function has formula as the following table: TH The regression function at the channel grade with two structural types Rectangular sewer: Box sewer: TH1 Ckc3 = 0,6417*ln(Qkc3) + 0,6246; (3.11) Ckc3 = 0,4731*ln(Qkc3) + 0,487; (3.8) TH2 Ckc3 = 0,6764*ln(Qkc3) + 0,7114; (3.12) Ckc3 = 0,5179*ln(Qkc3) + 0,5736; (3.9) TH3 Ckc3 = 0,7010*ln(Qkc3) + 0,7983; (3.13) Ckc3 = 0,5628*ln(Qkc3) + 0,6603; (3.10) Where, Ckc3 is the construction investment cost in billion Dong per 100m, Qkc3 is discharge of the channel grade in m3/s * The regression relationship between discharge and construction investment cost of channel grade 1, 2: The channel grade and in researching system is the trapezoidal channel The author used the data of Nhue River to calculate for channel grade and The regression function for the dredged and reinforced roof channel: TH1: Cc1-2 = 0,000003*(Qc1-2)2 + 0,0032*Qc1-2 + 2,393; (3.14) TH2: (3.15) Cc1-2 = 0,000003*(Qc1-2) + 0,0041*Qc1-2 + 2,3192; 15 TH3: Cc1-2 = 0,000002*(Qc1-2)2 + 0,0051*Qc1-2 + 2,2455; (3.16) The regression equation for the dredged channel: TH1: TH2: TH3: Cc1-2 = 0,000003*(Qc1-2)2 + 0,0032*Qc1-2 – 0,0558; (3.17) (3.18) (3.19) Cc1-2 = 0,000003*(Qc1-2) + 0,0041*Qc1-2 - 0,1296; Cc1-2 = 0,000002*(Qc1-2) + 0,0051*Qc1-2 - 0,2034; Where: Cc1-2 Investment cost for channel grade and (billion/100m); Qc1-2 Designing discharge for channel grade and (m3/s); c The detention pond Assuming the detention pond was built and reinforced roof by stone The regression function: TH1: Chdh = 4,8997*(Fho) + 9,7424; (3.20) TH2: Chdh = 6,2804*(Fho) + 9,7424; (3.21) TH3: Chdh = 7,6611*(Fho) + 9,7424; (3.22) Where, Chdh is construction investion and site clearance cost in billion, Fho is detention pond area in The Software Eview 6.0 is applied to test the regression function on the probability of error and stability 3.3.3 The specific regression function for the West basin of Hanoi From the general regression function and established regression function, the specific regression function has formula as following: C = f1(Qđm) + f2(Qc1-2) + f3(Qkc3) + f4(Fh) => 3.4 Establishing the scenarios of layout of the detention ponds Based on the literature on drainage plan for the west of Hanoi, the drainage basin is divided into 03 drainage headwork The detention pond area selected by percentage of drainage area ranged from 0% to 6% About detention pond layout, this study considered 03 scenario groups: (1) pond concentrated in the drainage headwork, (2) pond distributed along the main channel (PT1), (3) pond distributed along the main channel and branch channels (PT2) a The scenarios of the detention pond concentrated at the drainage headwork (TT) 16 The author proposes 12 scenarios of the detention pond that concentrated at the drainage headwork and had the same area ratio in the 03 drainage headworks The area ratio of detention pond ranged from 0% (no pond) to 6% Otherwise, the authorlso proposes 24 scenarios of the different detention ponds in every drainage headworks Totally, 36 scenarios were considered b The scenarios of the distributed detention pond * The scenario of detention pond distributed along the main channel (PT1) including 11 scenarios, each scenario has 11 locations of detention pond * The scenario of detention pond dstributed along the main channel and branch channels (PT2) including 11 scenarios, each scenario has 38 locations of detention pond 3.5 The result 3.5.1 The results of simulation of the flow corresponding to each scenario The discharge in calculating or modeling is the average value in hour According to designing standard, this value will be used in designation 3.5.1.1 The scenarios of the detention pond concentrated at the drainage headwork (TT) Figure 3.10 The relationship between upstream discharge and the detention pond area Figure 3.11 At Lien Mac inflow when the detention pond area changing At the upstream, discharge decrease when the pond area increases The reduction is smaller and smaller (Figure 3.10 and 3.11) The peak discharge summary of the headworks reaches to minimum at TT666 (pond ratio 6%) When the pond area ratio is different at the headworks, the headwork discharge 17 summary reaches to minimum corresponding to pond ratio 5.3% (as scenario TT664) 3.5.1.2 The scenarios of the distributed detention pond The calculation results for the scenario group (PT1) and (PT2) present the total peak discharge at upstream and total peak discharge at channels are minimum when the pond ratio is 4.35% (as scenario PT1-6) and 4.58% (as scenario PT2-6) corresponding to the scenario groups PT1 and PT2 3.5.1.3 Comparision between scenarios of concentrated and distributed detention pond The comparision is shown in the following diagram: Figure 3.15 The diagram of relationship Figure 3.16 The diagram of relationship between the total of peak discharge and the detention pond area between upstream discharge and the detention pond area The headwork peak discharge reduces in all scenario groups (TT, PT1 PT2) In which, the scenario of distributed detention pond along the main chaneel and branch channel (PT2) gave out the minimum value (figure 3.15) The diagram 3.16 has shown that the peak discharge of the channel system corresponding to scenario (TT) unchanged (horizontal line) On the other hand, both of the scenarios (PT1) and (PT2) decreased strongly Especially, the scenario of pond distributed along the main channel and branch channels have strongest reduction (the pink line) Summary: Regulating effect of the pond depends on not only the pond scale, but also the form layout (concentrated or distributed) Considering overview of the system, if the distribution of detention pond is more and more large, the effect of peak discharge is more and more increase 18 3.5.2 Applying the regression function to determine the reasonable scenario of detention pond for the west of Hanoi Applying the established regression functions in the previous parts to determine the reasonable scenario of the detention pond, inluding: 3.5.2.1 The scenarios of the concentrated detention pond a In case of 100% agricultural land (TH1) Figure 3.24 The graph showing the relationship between the detention pond area and the construction investment cost of work items corresponding to structural plan (GTT1) Figure 3.25 The graph showing the relationship between area ratio and construction investment cost of whole system Remark: GTT1: The box channel grade 3, reinforced main channel, headwork and detention pond were built; GTT2: The round channel grade 3, reinforced main channel and detention pond was built; GTT3: The box channel grade 3, channel grade and dredging only and headwork and detention pond were built The evolution trend of the construction cost of each work item is shown in figure 3.24 Considering the figure 3.25, the graph presented to 03 form structures forms is parallel with each other and every line existes a minimum point with the pond area ratio of 2.5% From the calculated results of 36 scenarios, the proposal on form layout of detention pond that concentrated in the headwork in the western system of Hanoi when area clearance of 100% is agricultural land achieve the reasonable 19 value (2.5% are arranged for all 03 drainage headworks, 2.91% are unevenly arranged on drainage basin,) (Lien Mac 4%, Thai Yen 2%, Yen Nghia 2%) b In case of 85% agricultural land ( TH2) 70% agricultural land (TH3) After calculating with 36 scenarios of layout form with 03 structural forms corresponding with 02 cases, it is totally 216 calculating cases, comparing the calculated results, it can be concluded as follows: For the drainage system in the west of Hanoi while unit prices of site clearance is different (TH2, TH3) and the layout form of detention pond is concentrated at upstream, the construction investment costs have minimum values while area ratio was 2% (evenly arranged for all 03 drainage headworks), was 2.91% (unevenly arranged: Lien Mac 4%, Thai Yen 2%, Yen Nghia 2%) Therefore, in the case detention pond concentrated in the headwork, reasonable scale of the detention pond is 2% (arranged for all headworks), 2.91% (unevenly arranged for all headworks) 3.5.2.2 The scenarios of the distributed detention pond a In the case of 100% agriculture land ( TH1) The calculating results for 02 scenario groups of distributed pond be shown as figure 3.25 a/ The distributed pond PT1 b/ The distributed pond PT2 Figure 3.26 and 3.27 The graph showing the relationship between area ratio and construction investment cost of whole system According to the figure 3.26 and 3.27, the graph have 03 parallel corresponding to 03 strutural forms, each line exists a minimum point (minimum value) on construction investment costo n the whole system In the scenario of distributed pond in the main cannel (PT1), the construction investment cost correspond to 20 area ratio 3.62% considering on the scenario of distributed pond in the main cannel (PT1) and 3.82% considering on the scenario of distributed pond in either main cannel and sub-channel (PT2) b In the case of 85% agricultural land ( TH2) and 70% agricultural land ( TH3) The calculating results on TH2 and TH3 is similar to TH1 The trend of minimun point of total construction investment coston whole system move close to the origin when the site clearance cost increase In conclusion: For the west of Hanoi when arranged the distributed pond in the main cannel, the minimum point of construction investment cost (ĐTXD) in the whole system is at the location of 3.62% of pond area corresponding to TH1, 3.26% corresponding to TH2 and 2.90% corresponding to TH3 When arranging the distributed pond on main or sub- cannel, the minimun cost of construction investment costo n whole system is 3.82% corresponding to TH1, 3.05% corresponding to TH2 and 2.67% corresponding to TH3 3.5.2.3 Comparision between each scenarios of pond layout Chosing one type of structural form to compare: Figure 3.28 The graph showing relationship between area ratio and construction investment cost at the headwork Figure 3.29 The graph showing relationship between area ratio and channel construction cost For the headwork: The construction investment cost of the 03 scenarios stands separatly proving the layout form (concentrating or distributing) greatly affect to the construction investment cost For the cost of clearance, this effect is negligible (Figure 3.28) 21 For channel systems: The separation of graph present the construction investment cost of 03 groups (100%, 85%, 70% of agricultural land for compensation) separately It is easy to comment that when the compensation increases, the construction investment cost increase The detention pond is more and more diffuse, the construction cost derease The total construction investment cost of all work items corresponding to structural form exist a minimum point This is value of the reasonable scale of the detention pond 3.6 Conclusions of chapter The results in chapter showed that there is a close relationship between construction cost and detention pond’s size or layout form In general of the same size, if the detention pond distribute increasingly, the construction cost is more and more decrease and vice versa Inaddition, the reasonable area of detention pond (corresponding to the minimum point of construction cost) depend on unit price of site clearance When compensation unit price increase, the area ratio tends to reduce and vice versa CONCLUSION AND RECOMMENDATION I Conclusion The thesis reviewed the status of distribution and use of detention pond as well as the relevant studies in VietNam and in the world The thesis also pointed out the urgency, novelty of research problems in the thesis, not overlapping with the studies which have been published previously in Vietnam and abroad The thesis developed a method to solve the problem of determining rational size and layout of detetiom pond to reduce the construction costs of the mixed agricultural - urban region The method includes: identifying the calculation steps, building the objective function, specifying the objective function components The thesis also selected the mathematical model Storm Water Management Model (SWMM) 5.0 of EPA, USA to simulate rainfall-runoff for 22 urban areas, and the used “on-farm reservoir” model to calculate outflow from the agricultural areas SWMM 5.0 was validated corresponding to the study area based on observed data The validation results have determined the model parameters in the study area These parameters were used for the next calculations of the thesis and certify the reliability of the model in simulating hydrologic - hydraulic process for the drainage system in western part of Hanoi The thesis has developed the objective function for study basin – the West of Hanoi, the components of the objective function are calculated and determined corresponding to price of construction in at the fourth quarter of 2013 The regression relationship between investment costs and discharge between the construction cost of the pond and pond area were calculated for 03 cases of clearance, the regressions were achieved in validating the probability of mistakes by Eview 6.0 software This is a new research methodology considering the whole system in terms of hydraulics, hydrology and economics The method presented in this thesis can be applied to other areas with similar conditions, and is probably extended to establish operation procedures reasonably or design and upgrade drainage system including head channel system and detetion pond Detetion pond only regulates peak flow for works behind pond, peak discharge decrease rate is proportional to the area of the pond, pond separately distributed have more effective regulatory than clustered at headworks because many work items are reduced peak flow The calculation results showed that the option having the lowest total investment cost of construction depends on the smallest construction unit prices, unit costs for site clearance compensation When compensation cost is higher, reasonable plan is tended to small scale detetion pond Cost of construction depends on the construction unit prices, clearance unit prices, forms and reasonable detetion pond distribution will vary between localities 23 II Recommendation Detetion pond provides many benefits in addition to regulating stormwater to reduce flooding such as improving the environment, creating recreation centers, entertainment, and sports communities Accordingly, for urban areas, industrial zones, when considering the construction of detetion pond, it is necessary to consider the overall interests of the detetion pond to the area to confirm the real benefits of the project III Limitation of the Thesis The thesis considered the pond located nearby the canal, rainwater flowing into and out of the pond in term of gravity, but not considered yet the pond located on the canal, and pond with regulation works It is necessary to study cases having agricultural land in different clearance scenarios between work items in the system 24 PUBLICATIONS OF THE AUTHOR Luu Van Quan, Tran Viet On (2015), Application of a method for determination of location and appropriate scale of a detention pond - a case study: drainage system in Western Hanoi, Science and Technology Journal of Agriculture & Rural Development, Issue 18-2015, pp 49-56 Luu Van Quan, Tran Viet On (2015), A method for determining area (or volume) of a stormwater detention pond for a new urban area, will be published in Journal of Water Resources & Environmental Engineering, Issue 51-2015 Luu Van Quan, Tran Viet On (2015), Optimal construction cost for urban drainage systems: A case study in a drainage basin, Western Hanoi, Journal of Water Resources & Environmental Engineering, Issue 48/3-2015, pp 92-98 Luu Van Quan, Tran Viet On (2014), Relationship between detetion pond areas and pond effluent flows in an urban drainange system: Case study of Dam river basin in drainage system Hanoi, Journal of Water Resources & Environmental Engineering, Issue 47/12-2014, pp 03-08 Luu Van Quan (2014), The research on the optimum layout of detention pond is to reduce the urban drainage system's scale (applied to the drainage system of the west of Hanoi), the university - grade scientific research Luu Van Quan, Nguyen Tuan Anh (2013), Situation of using detetion pond in storm water drainage system in some cities of the Northern delta, Viet Nam, Journal of Water Resources & Environmental Engineering, Issue 41/6-2013, pp 1620 25 [...]... is possible to apply these simulations to test the model Table 3.2: The evaluation table on the error of calculating and measuring process (02 rains) Max discharge (m3/s) Measuring Station Hà Đông Đồng Quan Hà Đông Đồng Quan Daily rain Total discharge (m3) Error Measu ring Calcul ating Error Calculatin Measuring g (%) Error (%) S/ 22/5 - 89,60 93,92 4,82 8.819,67 8.773,56 0,52 0,08 26/5/2012 101,19... the project in the region Establishing of regression function between the construction costs and discharge or area is to determine the objective function’s components In this study, both of two ways has chosen to build the specific objective fundtion to studying areas The order of elaboration of the regression function for each item is implemented as follows: * Drainage headwork is pumping station The... (2.25) and (2.30, 2.31, 2.32, 2.33a, 2.33b) established, the specific objective function has following formula: C = f1(Qđm) + f2(Qk1,2) + f3(Qkc3) + f4(Fh); (2.34) 2.3.5 Applying the objective function to choose an optimal scenario a The relationship between discharge and area of the detention pond The relationship between total peak discharge on the drainage headwork, total peak discharge on channel system... parameter is to simulate the scenario of the research problem 3.2.2 Validation results Table 3.1: The evaluation table of the error of the calculating and measuring process Measuring station Daily rain Hà Đông 24/8 - Đồng Quan 28/8/2010 Max discharge (m3/s) Total discharge (m3) Measur Calcu Error Calculati Error Measuring ing lating (%) ng (%) Error S/ 81,58 82,78 1,48 8.052,9 8.076,72 0,70 0,15 105,66... n: Number of cannals in system, T: Number of detention pond in system b Constraint condition The constraint conditions in the simulation: 1) Fngập = 0; no flooding in the case of calculating rain 2) Fhồ < (a%* Flưu vực); detention pond area is smaller than a% total drainage area 3) Construction the detention ponds are workable 4) Assuming the studing field has defined boundaries, planned ground of... were smaller than allowance 13 Therefore, the calculating line and measuring line is well reasionable with each other The SWMM can be appied to calculate for this thesis 3.2.3 The model parameters were chosen after testing a The parameters of padded surface - Coefficient of surface roughness with hard coating: n = 0.025 – 0.15 - The parameters on the characteristics of soil permeability: Maximum permeable... relationship between the total of peak discharge and the detention pond area between upstream discharge and the detention pond area The headwork peak discharge reduces in all 3 scenario groups (TT, PT1 và PT2) In which, the scenario of distributed detention pond along the main chaneel and branch channel (PT2) gave out the minimum value (figure 3.15) The diagram 3.16 has shown that the peak discharge... reasonable 19 value (2.5% are arranged for all 03 drainage headworks, 2.91% are unevenly arranged on drainage basin,) (Lien Mac 4%, Thai Yen 2%, Yen Nghia 2%) b In case of 85% agricultural land ( TH2) và 70% agricultural land (TH3) After calculating with 36 scenarios of layout form with 03 structural forms corresponding with 02 cases, it is totally 216 calculating cases, comparing the calculated results,... cost of construction investment costo n whole system is 3.82% corresponding to TH1, 3.05% corresponding to TH2 and 2.67% corresponding to TH3 3.5.2.3 Comparision between each scenarios of pond layout Chosing one type of structural form to compare: Figure 3.28 The graph showing relationship between area ratio and construction investment cost at the headwork Figure 3.29 The graph showing relationship ... constraint conditions in the simulation: 1) Fngập = 0; no flooding in the case of calculating rain 2) Fhồ < (a%* Flưu vực); detention pond area is smaller than a% total drainage area 3) Construction... or area is to determine the objective function’s components In this study, both of two ways has chosen to build the specific objective fundtion to studying areas The order of elaboration of the... formula: C = f1(Qđm) + f2(Qk1,2) + f3(Qkc3) + f4(Fh); (2.34) 2.3.5 Applying the objective function to choose an optimal scenario a The relationship between discharge and area of the detention pond The