Planning and design of composite network (one network for wastewater and rainwater drainage) By Hayder Kamil Abdulkareem Environmental Planning Department Physical Panning College, University of Kufa, Najaf, Iraq Email: hayderk.abdulkareem@uokufa.edu.iq December 15, 2014 ABSTRACT Nowadays, drainage networks, whether that was wastewater or storm water drainage networks are considered as one of the necessary infrastructure basics in modern cities. This research is focusing on planning and designing one drainage network “for a dual purpose” instead of the two networks that used one for wastewater and the other one for rainwater drainage, as they are called separated Drainage networks. Therefore, this network is working on wastewater and on the rainwater drainage on the same time. That reduces the cost by reducing amount of excavations and number of the pipes as well the wages for the workers who work on that project. This network would be perfect in Arab countries like Iraq because the amount of the rainfall is not that much and it happens only on the winter season for almost two or three months, not like the other western countries or Australia. This research is following the global standardization in finding the optimal way of the designing a network such as finding the pipe slope and velocity of the water inside the pipes. Also, to compare it with minimum and the maximum velocity permitted, as well as finding the discharges and levels of pipes’ places in trenches and that depending on essential principles of designing of the network. The research also includes the planning, designing and drawing a typical longitudinal sections for the Arab city and to be considered as a model that could be used for the planning and designing for any other cities according to the least possible cost. All in all, the most important characteristic of this research is to adopt the discharging of more than a pipe in one direction within the inspection room so as to minimize the amount of excavation and reduce the diameters of the large pipes. For example, instead of choosing a pipe with a large diameter we can use two or more pipes with less diameter and that consider as a special feature worthwhile when you do not desire to the use of large diameters or the unavailability of that kind of pipes. 1. Introduction Libyan government has planned to implement sewerage systems for the people living in Tominah settlement with objective of providing appropriate infrastructure, including disposal of sewage and storm water based on sound environmental practices under the "project for design of sewerage and storm water collection systems". There is no existing sewerage system or collection system for storm water in Tominah settlement. Therefore, this research proposed "planning and designing of combined network to disposal of wastewater and storm water in one network for Tominah settlement ".This type of networks will be very successful and very active because the amount of rainfall limited by two or three months only through winter season in Tominah settlement and implementation of combined network will lead to reduce the cost compared with cost of implementation two networks one for disposal of wastewater and the second for disposal of storm water. 1.1. Geographical location Tominah is a small settlement of currently around 1,000 inhabitants in the east of Mosratah city. It is located in the midst of an agricultural area of more than 6,000 ha at an elevation of approximately 20 m above mean sea level. To the west of the agricultural area, the land becomes dry and less and less productive. The settlement has a fairly good connection to Mosratah and the coastal highway to Tripoli. The area of the settlement is 44.5 ha. Figure (1.1) enclosed shows the geographical location of Tominah. [1] 1.2. Climate The climate data for Tominah settlement are presented in Table (1.1). Table (1.1) climate data S. No. Description Temperature(Cₒ)* 1 Average annual rainfall ---- 270 ---- 2 Maximum daily rainfall ---- 155 ---- in year 1986 Rainfall(mm)* Humidity (%)* 3 Mean annual temperature 20 ---- 4 Mean monthly air 27.3 ---- ------- Temperature in August 5 Mean monthly air 13.2 ---- ---- ---- ---- 72 Temperature in January 6 Mean yearly relative air Source: * Libyan meteorological department climatological section The nearest rain station is in Mosratah where the average maximum daily rainfall is observed to be less than 37 mm. 1.3. Population Table (1.2) shows the population figures which are adopted for design in this research. The details are summarized as in the table (1.2) below: Table (1.2) present and projected population S. No. Settlement of Tominah 2011 Saturated population 1 Inside the master plan area 1500 2250 2 Outside the master plan area 168 252 3 Population total 1668 2502 *Source: Office of Civil Registry. 1.4. Master plan The master plan of Tominah settlement, which shall form the basis for all the design presented in this research, is shown in Figure (1.2). The area assigned to different land use patterns is summarized in Table (1.3). [1] Table (1.3) land use pattern S. No. Type of land use Symbols Area (ha) 1 Residential R2,R3 2 Education, health and social welfare, F1,F2,F3 6.27 religious and cultural 6.73 3 Sports and recreational, protection zone S1,S4 13.75 4 Commercial C 2.89 5 Light industries and warehousing I2 0.90 6 Agricultural residential/ service for agricultural As 2.48 7 Public facilities and public utilities U 0.125 8 Road and open area --- 11.35 2.1. Problem statement As we said above, there is no existing collection system for storm water in Tominah settlement. So when it rains in large quantities during winter that leads to submerge roads by storm water and that will lead to difficulty of movement during the settlement. The resulting pools of rainwater falling in some parts of Tominah settlement lead to the spread of diseases and epidemics. Also there is no existing sewerage system in Tominah settlement and this lead to pollution of drinking water, which depends on rainfall in that the settlement. 2.2. Objective The objective of this research represents by creating of strategic planning horizons according to common standards in the field of planning and designing of combined networks to disposal of wastewater and storm water .we can illustrate that as shown in the Table (2.1): Table (2.1) strategic planning horizon Strategic horizon Objective Short term strategy Include all such actions required to provide Planning and designing of combined network to disposal of wastewater and storm water in Tominah settlement Long term strategy To reach the target level of services to Capacity required for the saturated population 2.3. Scope of study Scope of study represents as follows: 2.3.1. Planning and designing combined network of disposal of wastewater and rain water according to global standards in Tominah settlement. 2.3.2. Most cities in the Arab countries, including Iraq's cities devoid of typical and developed infrastructure, particularly in the field of wastewater and storm water networks. Therefore, this study seeks to contribute to the development of infrastructure in order to create integrated infrastructure in the Iraqi cities. 2.3.3. This study seeks to develop the relationship between the university and community by offering research which seeks to find solutions to the problems suffered by the community in the field of infrastructure. Researches that lead to the development of infrastructure in the field of combined networks to drain rainwater and wastewater meet an essential requirement of the society demands. 2.3.4. This study seeks to improve the environmental situation in Iraqi cities as well as Arab cities during the disposal of wastewater and rainwater because the existence of such polluted water inside the cities helps the spread of diseases and epidemics. 3. Theory of research 3.1. Sewerage This section presents standard design criteria for sanitary sewer systems. The criteria presented have been standardized to reflect typical installations. It is understood that certain situations may require deviation from the criteria herein. 3.1.1. Sewer design criteria Sewerage system include collection of wastewater from each source, transport, including pumping stations, delivery to a treatment facility, treatment, and disposal of solids generated during the treatment process . Storage and handling of Treated Sewage Effluent (TSE) is considered part of the irrigation system. In general, sewer capacity should be designed for the estimated ultimate contributing population and full expected development of industrial and commercial areas. TOMINAH SETTLEMENT FIGURE (1.1) GEOGRAPHICAL LOCATION 3.1.2. Sewerage flow projections For community wide sewage flow projection, design average sewage flows are determined as 80% of the design average water demand rate. Table (3.1) lists average a water and sewage flow rate based on community population size. [1] Table (3.1) Unit flow rates for sewage [1] Average water demand,m3/d,[Qave] Population Average potable Domestic [inhabitants] water demand sewage [Q] flow[Q] (water distribution pipe leakage, pipe flushing, lawn irrigation etc. Included) < 3,000 Q = 150 l/d/c Q = 120 l/d/c 3,000-20,000 Q = 180 l/d/c Q = 145 l/d/c 20,000-50,000 Q = 200 l/d/c Q = 160 l/d/c 50,000-100,000 Q = 250 l/d/c Q = 200 l/d/c 100,000-500,000 Q = 300 l/d/c Q = 240 l/d/c >500,000 Q = 350 l/d/c Q = 280 l/d/c Design maximum sewage flows shall be calculated by using a Peaking Factor (PF) for all sewage flows from a known or assumed tributary population, based on the Babbitt Formula, as follows: �� = . ∗ �� � − …. )3.1) The PF shall be used to project maximum sewage flows from a tributary area for tributary areas with contributing population equal to or greater than 500 persons. For tributary areas with fewer than 500 persons, an alternative method of estimating peak flows is allowable. For concentrated commercial and light industrial area, Table (3.2) presents flow for selected commercial activities. Table (3.2) unit flow rates for sewage [1] Type/activity Unit flow rate (l/d/c) Office 54 Commercial 72 Hotels 380 Government and cultural 54 Exhibition halls 45 Light industry and warehousing 72 Airport passenger 18 Airport employee 54 Catering facility 7.2 Guard houses 280 Petrol station 100 Royal hall 18 For heavy industrial sewage flow project, a detailed evaluation is required, industryby-industry, on a case-by-case basis. [1] 3.1.3. Hydraulic design Hydraulic design shall be used Manning equation to calculate velocity of wastewater inside diameter. Roughness coefficients based on the pipe material as shown in Table (3.3) shall be used. The roughness coefficient is a measure of the variation and magnitude of protuberances on the interior surface of the pipe. The roughness therefore is a function of the pipe material, age, and condition. Poor pipe conditions are to be assumed for sewage system designs. [1] Table (3.3) typical roughness coefficients [1] Manning's coefficient, n Pipe material Normal Poor uPVC 0.010 0.013 GRP 0.010 0.013 HDPE 0.010 0.018 RCP 0.012 0.016 0.012 0.016 DIP w/mortar lining 3.1.4. Flow velocities The design flow velocity limits are listed below. [1] Table (3.4) minimum and maximum velocities in sewer pipes [1] Minimum velocity Maximum velocity Design velocity (m/s) (m/s) (m/s) Pipe description Gravity pipe 0.5 3.0 0.75 Pressure pipe 1.0 2.0 1.5 3.1.5. Depth of flow The following table shows the recommended depth of flow in gravity sewer lines. The ratio (d/D) is the ratio of the flow depth (d) to the nominal pipe diameter (D). [1] Table (3.5) minimum and maximum depth of flow in sewers at Peak Flows [1] Description Maximum(d/D) Minimum (d/D) Trunk sewer lines 0.75 0.5 Main and lateral sewer lines 0.85 0.5 3.1.6. Pipe gradients In order to achieve the required minimum velocity in sewer lines, pipes should be designed by observing the minimum gradients listed in the table below. [1] Table (3.6) pipe gradients [1] Pipe diameter Minimum gradient(mm/mm) (mm) (velocity 0.75 m/s) 200 0.00500 250 0.00370 315 0.00270 400 0.00200 500 0.00150 600 0.00120 700 0.00100 800 0.00085 900 0.00070 1000 0.00060 1100 0.00055 1200 and larger 0.00050 3.1.7. Pipe materials Sewer pipe materials have been selected to be consistent with local standard practices, based on economics and local availability. The following materials shall be used for various pipe sizes: 3.1.7.1. For sewer mains equal to or less than 315mm in diameter, uPVC shall be used. For sewer mains larger than 315mm in diameter, GRP shall be used. Other corrosion resistant materials, such as high density polyethylene pipe (HDPE) OR vitrified clay pipe (VCP), may be considered. 3.1.7.2. For pressure mains, GRP or HDPE shall be used. RCP and DIP with mortar lining may be considered for special circumstances. [1] 3.1.8. Minimum cover requirements The minimum cover recommended is 1.2 m above the pipe crown, in order to protect from external loads. If the available cover is less than 1.2m, then additional protection such as full concrete encasement or the use of concrete protection slabs shall be provided. In special areas with heavy loading, up to 2m of cover may be required over the crown of the pipe, depending on appropriate structural evaluation for the specific situation. The actual cover required for construction and access may be greater than that required solely for structural integrity. For example, the minimum cover required by the physical dimensions of a typical access manhole is 2m above the pipe crown. However, for small pipes less than or equal to 315mm in diameter, the required cover may be less than 1.2m. If inspection chambers are installed rather than manholes, 1.0m of cover will suffice. The maximum cover depth recommended is approximately 10m. This maximum depth is consistent with typical pipe installation standards and manufacturer recommendations. Should the actual cover be greater than 10m, pipe materials and loads should be evaluated and a higher strength class of pipe utilized. For pipes installed at less than these minimum values or at excessive depth, concrete encasement may be required to protect the pipe from damage. Alternatives of different pipe size at a different slope should be considered before designing the pipelines outside of the specified depth ranges. In all cases, the pipe minimum and maximum depths shall be in conformance with the pipe manufacturers' recommendations. [1] 3.2. Storm water HIB has developed standard design criteria for storm water drainage systems. The criteria presented have been standardized to reflect typical installations and to support the designing and planning of infrastructure. It is understood that certain situations may require deviation from the criteria herein. 3.2.1. Storm water design criteria Storm water facilities design must be compatible with the appropriate storm water discharge and disposal options. For example, it must be determined if the storm water drainage will be removed from the site via outfalls, or if it will be retained on site and the water allowed to infiltration into the groundwater and/or evaporate. In general, Libya has a dry climate. Rain storms in Libya are intense, short in duration, and infrequent. Along the Mediterranean coast, the wettest months are from September to February, with lesser rainfalls recorded even in the drier months. The average annual rainfall in Tajura is 288mm based on 40 years of data. Other areas in the country may have significantly different rainfall records. Thus, the approach to storm water drainage design must consider the local rainfall records for determining the appropriate design storm. [1] 3.2.2. Design storm Design rain storms are typically determined based on recurrence interval. For local drainage facilities, a five-year storm shall be used for calculating storm water runoff and sizing drainage collectors and mains. For major drainage facilities, a fifty-year storm shall be used for calculating storm water runoff and sizing the major drainage facilities. Major drainage facilities are large facilities, such as wadis, which receive inflows from multiple local drainage areas. Major drainage may also be critical drainage areas, such as airport or underpasses, where localized flooding is unacceptable. The designer is responsible for collecting and evaluating the available rainfall data and calculating the intensity and duration of design storm appropriate for each specific project location. Copies of all rainfall data used for determining the design storm shall be submitted together with the calculated design storm intensity and duration. Examples of typical design storms are shown in the following Figure (3.1) and Figure (3.2). [1] Figure (3.1) example 5-year, 1.5-hour duration storm [1] Figure (3.2) example 50-year, 24-hour duration storm [1] 3.2.3. Runoff coefficients Runoff for the design storm event shall be calculated based on the Rational Method, whereby the runoff flow, Q, equals a coefficient, C, times storm intensity ,I, times catchment area, A. Runoff coefficients based on ground surface type and land use are provided in Table (3.7) and shall be used for design runoff flow calculations. [1] Table (3.7) runoff coefficient values [1] Area description Runoff coefficient, C Categorized by surface asphalt 0.7 to 0.95 Brick 0.7 to 0.85 Concrete 0.8 to 0.9 Sandy soil 0.05 to 0.2 Clayey soil 0.13 to 0.35 Categorized by use Administration 0.5 to 0.75 Educational 0.8 Center 0.8 Medical facilities 0.6 to 0.8 Religious and cultural facilities 0.7 to 0.8 Agricultural 0.3 to 0.5 Unimproved 0.1 to 0.3 Parks and playgrounds 0.1 to 0.25 Playground( non-asphalt or concrete ) 0.2 to 0.35 Business districts 0.7 to 0.95 Industrial Light 0.5 to 0.8 Heavy 0.6 to 0.8 Residential Small villas (<2500m2) 0.3 to 0.5 Large villas (>2500m2) 0.25 to 0.4 Apartments 0.65 to 0.85 3.2.4. Other flows In addition to the rainfall runoff, the storm water system will need to accommodate dry weather flows into the system. These will include any road runoff from groundwater dewatering, over-irrigation, residential car washing, or other such activities. Groundwater that is pumped or removed via land drains in order to lower the groundwater table for construction or after construction will most probably be disposed of the storm water system. The amount of dewatering that may be required can be estimated by using a groundwater lowering computer model. It is expected that, in areas where the groundwater table is within 2m of pavements or structures, pavement surface land drains will be installed to lower the groundwater table. [1] 3.2.5. Hydraulic design Roughness coefficients based on the pipe materials as shown in Table (3.3) shall be used. 3.2.6. Flow velocities The minimum flow velocity allowed through drainage conduits (to prevent excessive settling of solids) and the maximum flow allowed (to avoid abrasion of the gravity conduits) shall be as shown in Table (3.4). 3.2.7. Clear times Allowable clear times have been established for the different types of area where new storm water drainage may be required. These times refer to the period of time after the end of a storm event during which limited water ponding is permitted. Table (3.8) identifies the clear time for each of the main service areas. [1] Table (3.8) allowable clear times for 5-year, 1.5 – hour design storm [1] Area designation Clear time, hours Comments Freeways/expressway 0 See note 1 Arterial road 0 See note 1 Collector road 3 Local roads 3 Roadway underpasses 0 Parking lots 6 Airport runways 0 See note 1 Airport taxiways 0 See note 1 Airport infield 24 See note 2 Drainage detention ponds 120 See note 2 Undeveloped land NCT See note 3 See note 1 Notes: [1] 3.2.7.1. Water shall be cleared within the timeframe of the storm, and flooding during the storm will be minimized to avoid unnecessary disruption of traffic. 3.2.7.2. Shorter clear times shall be sought where possible. 3.2.7.3. NCT = no clear time. Clearing of this area shall be as quick as practicable after other areas have been drained. The clear times for roads and parking areas shall be 6 hours. The maximum allowable depth of flooding is the height of a road curb which is 150mm. 3.2.8. Depth of flow The design depth of flow for all drainage pipes is assumed to be full, and with a surcharge as determined by the designing model. The system may be designed to operate under surcharge flow conditions for most pipes in order to achieve the required clear time. [1] 3.2.9. Pipe materials Table (3.9) lists allowable pipe materials for various pipe sizes. The minimum pipe diameter permitted for drainage system gravity collection pipes is 250mm. land subdrains under detention ponds and infiltration areas can be 200mm in diameter. Connection to street gutter and other inlets may also be 200mm diameter, and shall have a slope of 2 percent or greater. [1] Table (3.9) allowable pipe materials [1] Diameter (mm) Pipe material 200 to 500 uPVC or GRP 600 to 2000 GRP , HDPE or RCP > 2000 Lined RCP RCP pipe shall be provided with protection from sulfide corrosion, such as PVC or GRP lining or possibly a sacrificial lining of mortar with calcareous (limestone) aggregate. 3.2.10. Manholes [1] Manholes are used to provide access to drainage lines. They shall be provided at each change in direction (vertical or horizontal) and connection of two or more lines. Manholes are to be placed at least every 100 m or the limit of existing pipe cleaning equipment, whichever is smaller. In particular, manholes should be installed where necessary to facilities cleaning and access. The manhole structures are normally circular in shape, with minimum diameter of 1,000 mm. manholes shall be constructed of reinforced concrete with GRP or other corrosion proof lining. Details of access and constructions shall be in accordance with established HIB or other standards and details. 3.3. Method of the design We can summarize design steps as follows: 3.3.1. Storm water flow rate (Qr) We can calculate storm water (Qr) from Rational Method .for all basins smaller than 160 acres, the Rational Method shall be used to calculate runoff for both the initial and major storms. The formula for the Rational Method is as follows: Qr = C * I * A * 1/ (1000*3600) … )3-2) Where Qr = Storm water flow rate, m3/s C = Runoff coefficient may be determined based on types of surface and land use classifications prescribed in Table (3.7). I = Rainfall intensity for the design storm, mm/hour. A = Drainage area, m2. [2] 3.3.2. Rainfall intensity (I) Rainfall intensity is calculated as follows: [1] �= 8 +�� … )3-3) Where tc = Time of concentration in (mm). [2] The time of concentration is calculated as follows: tc = t1 + t2 … )3-4) Where tc = time of concentration in (min). t1 = initial, inlet, or overland flow time in (min). t2 = travel time in ditch, channel, gutter, storm sewer, etc.in (min). Travel time in storm sewer (combined sewer) is calculated from following equation: �2 = � ��∗6 … )3-5) Where L = length of pipe (length of combined sewer) in (min). Vf = velocity of wastewater with storm water inside pipe in (m/s).[2] 3.3.3. Sanitary (wastewater) flow rate (Q1) inside the master plan area … )3-6) Q1 = Pn *Q*PF*1/ (1000*24*3600) Where Q1 = Wastewater flow rate inside the master plan area in (m3/s). Pn = Number of the population (saturated population) in (c). Q = Domestic sewage for one person in (l/d/c). PF = Peaking factor, PF equal to (3) in this study. [1] 3.3.4. Wastewater flow rate (Q2) outside the master plan area Q2 is calculated from (15% of Q1). 15% more sewage contribution is considered for master plan. 3.3.5. total wastewater flow rate (Qw) We can write the wastewater flow rate equation as follows … )3-7) Qw = Q1+Q2 Where Qw = Total wastewater flow rate in (m3/s). However, a more appropriate (Qw) is usually calculated as follows: [1] … )3-8) Qw = Pn *Q*PF*1/(1000*24*3600) *1.15 3.3.6. Total combined sewer flow (Qt) The total flow inside the pipe in the combined network is calculated from the following equation: … )3-9) Qt = Qr + Qw Where Qt = Total flow rate inside the pipe in (m3/s). 3.3.7. Population density (Pd) The population density for Tominah settlement is as follows: [1] = � � � � � � � � � � � � … )3-10) 3.3.8. Velocity of the flow inside the pipe (Vf) Velocity of the flow for open channel can be calculated from Manning's formula as follows: [3] � = ∗ . ∗ … )3-11) For circular conduit, Manning's formula becomes: � = . ∗ ∗� ∗ . … )3-12) Where Vf = Velocity in (m/s). n = Manning's coefficient of roughness. R = Hydraulic radius in (m). D = Internal diameter of the pipe in (m). S = Slope of hydraulic gradient 3.3.9. Discharge of the pipe (Qf) The discharge can be calculated from the following equation: [3] = . ∗ ∗� ∗ . … )3-13) Where Qf = Discharge in (m3/s). 3.3.10. Depth of flow (d/D) The ratio (d/D) is calculated from the following equation: [4] Y=0.979X6+2.688X5-12.37X4+14.85X3-8.007X2+2.639X+0.003 … )3-14) Where Y= Ratio (d/D), dimensionless. X = Ratio of (Qt/Qf), dimensionless. 3.3.11. Self-cleansing velocity (Vp) Self-cleansing velocity is calculated easily from the following equation: Vp = Vf * Z … )3-15) Where Vp = Self-cleansing velocity in (m/s). The minimum self-cleansing velocity adopted in this study equal to (0. 75m/s). Z = Ratio (Vp/Vf), dimensionless. Ratio (Vp/Vf) is calculated as follows: [4] Z=2.704Y6+6.565Y5-26.48Y4+28.11Y3-14.61Y2+5.106Y-0.004 … )3-16) 3.3.12. Upstream invert level Equation of upstream invert level is stated as follows:[4] UI = RL - SC- DN Where … )3-17) UI = Upstream invert level in (m). RL = Upstream road level in (m). SC = Soil cover in (m). DN = Nominal diameter in (m). 3.3.13. Downstream invert level Equation of downstream invert level is stated as follows: [4] LI = UI – S * L Where … )3-18) LI = Downstream invert level in (m). S = Slope of hydraulic gradient. L = Length of pipe in (m). 4. Results: While the table (4.1) shows results of design of combined network to drainage wastewater and rainwater for Tominah settlement, the table (4.2) shows alternative pipes have small diameters to the change some pipes which have big diameters. Figure (4.1) represents the master plan (top view) and it shows the necessary details of the combined drainage network for Tominah settlement as well as it illustrates details of transport line from combined network to proposal wastewater treatment plant. Figure (4.1) is divided into eleven parts in order to divide the master sheet for increasing clarity and to show more details. Figure (4.2) shows rainfall areas for each pipe from the combined drainage network and the rainfall areas are divided depending on ground surface type and slopes of the ground. Figure (4.3) shows distribution of the population for Tominah settlement. That information about the population Tominah is documented by many field trips to that region and with the aid of the previous population maps in addition to the previous statistical information. Figure (4.4) shows typical cross section of the streets (width of road =<10 m) and Figure (4.5) shows typical cross section of the streets (width of road >10m). While Figure (4.6) shows combined sewer trench details, Figure (4.7) illustrates connection to manhole with backdrop standard details of combined sewer connection. Finally Figure (4.8) shows ventilation shaft arrangement. All tables and figures above are shown in Appendix. 5. Conclusions and Recommendations 5.1. Conclusions: The most important conclusions that have been reached during this study are as following: 5.1.1. Through the results we have gotten, it has been noticed that the amount of rain falling water that entered to the combined network is much more than the sewage water and the fact that the population in the Tominah city in Mosratah, Libya is few, scattered, and non-contiguous. Though, as we have noticed that rainwater falls plentifully but in limited period during the winter. 5.1.2. Since Tominah settlement containing a small number of the population and they are diffused on a relatively large area therefore it is the best way to find the number of the population, which depends upon the calculating of sewage water amount that enter into the combined network which is considered as a method of the statistical direct counting through field tours. That method has been made in this research as it is the most accurate results from the method of calculating the number of people depending on the proportion of the population density. However, the first method adopted in this research can give an estimate of the number of future population which is more accurate than the second method. 5.1.3. Discharging rain water depends on rainfall area and its gradient which must be accurately determined based on the available maps of the area in addition to field tours. On the other hand, discharging rainfall water depends on the ground or land type (C factor) as Tominah settlement considers mostly an agricultural region that absorbs the majority of rainwater falling. That makes the amount of rainfall water which enters into the network is a little comparing with the total amount of the rainfall water that falls on that settlement. 5.1.4. The majority of the pipes diameters that have been used on the combined drainage network in Tominah settlement are the less pipes diameters which allowed to be used in the combined networks. Also, most pipes gradients are the less permitted ones. That can be considered as an economic design. 5.1.5. Since the topography of the area of that settlement and the big difference in the levels of the road on both sides of some of the pipes, that requires increasing the soil covering to (2.8 m) in some cases over the first pipe of the branch in order to maintain the soil covering of the subsequent pipelines within the international standards. 5.1.6. In case of a rocky soil or ground water, it is possible to reduce the soil covering above the pipe to (0.8 m) but in such a case the pipes should be covered with the concrete to save it from the breaking as a result of external loads imposed it. 5.1.7. In order to reduce the cost, it has to reduce the number of inspections basins (manholes) through the processing of connection the pipes that discharge the wastewater from the houses via the closest pipes network rather than connecting them with the main inspection basins only. 5.1.8. To reduce the economic cost, should reduce the diggings for the first pipes in the branches of network by allowing the velocity of the water that enters the pipes to the amount of (0.3 m / s). In addition, in case of depositions occur in that pipes would be removed in maintenance processing. 5.1.9. In the combined drainage network can ensure that accommodate any sudden increase in the wastewater volumes of the rain on the non-rain months, that because of the capacity of the pipes diameters which have adequate gradients to discharge the water. 5.1.10. In the combined drainage network the seepage water (infiltration water) amounts is not taken into the consideration at the network design. The fact that the calculated rainfall amounts is big whereas the pipes diameters are sufficient to absorb the infiltration water. 5.1.11. In the big cities, where combined drainage network are big and their diameters of pipes at the end of the network can reach to more than (1200 mm) and these pipes are might break, to avoid that the large-diameter pipes can be replaced by two pipes with smaller diameters. In this research the diameter pipes with size (500 mm) which are located at the end of the network have been replaced with two pipes diameter size (250 mm) and sometimes other variables changes in the design. 5.2. Recommendations: The most important recommendations in this research are the following: 5.2.1. Carry on studying to determine the water consumption per person for each city in Iraq or other Arab cities to determine the wastewater per person, as the amount of discharged wastewater equal to 80% of the amount of water consumption. 5.2.2. A study to gather information about the amount of rainwater falling in the previous years for each city in Iraq and identify those intervals of falling rains and the frequency of that in order to create a relationship that determines the rain intensity depending on the time of the concentrating to have more accurate design results. 5.2.3. Work on the water velocity that enters the combined drainage network not less than (0.75 m / s) in the main pipes. Especially at the end of the network so as to ensure that there is no deposition of heavy sand atoms inside the pipes that would be clogged them in the future. Nevertheless, if that was not possible as a result of reaching the depths of drilling to great depths, the velocity can be reduced to (0.6 m / s) as referred to in the most references. 5.2.4. Establish a strategy of residential districts that will be considered as plans of Najaf city in Iraq and other cities to ensure the establishment of an integrated infrastructure for these residential districts plans to improve the groundwater located in the cities of being contaminated by wastewater leaking from the dirty sewage water from septic tanks of the houses. References [1] Guidance document, design standards, The Great Socialist People's Libyan Arab Jamahiriya, Housing and Infrastructure Board (HIB), Program management Department (PMD), Revision No. 01, 21August 2008. [2] City of Boulder, Design and Construction Standards, Effective: November 16, 2000, Page 7-15, Boulder, CO. www.2005ch07. [3] " Spreadsheet Use for Partially Full Pipe Flow Calculation," Harlan H. Bengston, PhD, P.E., © engineering.com, Course No: C02-037, Credit: 2 PDH, Continuing Education and Development, Inc., info@cedengineering.com [4] Hayder kamil Abdualkareem, "Planning, Design and Drawing Storm Water Network in Cities", Abstracts of the Researches to the First Scientific Conference for Physical Planning College (2012), pag69. www.phsicalplanning.uokufa.edu.iq Parameters C = 0.1 Soil's cover = 1.0m. Nomenclature A = rainfall area for each pipe, m2. At = accumulation rainfall area, m2. ‫الخاصة‬ ‫صرف مي اأمط تعت ر من اأس سي ال ر ي‬ ‫صرف صحي أ ش‬ ‫الصرف س اء إ ك نت ش‬ ‫ش‬ ‫الح ي خص ص ً في عصرن الح لي ‪ ,‬ل لك ش ل ه ا ال حث ت طيط تص يم ش صرف‬ ‫ل ي التحتي في ال‬ ‫اح (م ج ) ب اً من ش تين اح لتصريف مي اأمط ث ني لتصريف مي الصرف الصحي ال عر ف ب سم‬ ‫الصرف ال ص ‪ ,‬بحيث تع ل ه الش ع صرف مي اأمط مي الصرف الصحي في آ اح‬ ‫ش‬ ‫ك ي هط مي اأمط‬ ‫ع اأن بيب أج الع ل‪ .‬ل‬ ‫لك من أجل تق يل ال من خا تق يل الح ري‬ ‫الغربي ‪,‬‬ ‫اخر م ل أسترالي مع م ال‬ ‫العربي ق ي ب ل ق ن مع‬ ‫فتر هط ل في العرا ب قي ال‬ ‫م س ‪.‬‬ ‫حيث ت حصر اأمط خا فصل الشت ء ض ن ش رين أ ثاث أش ر ل لك يعت ر ه ا ال من الش‬ ‫يش ل ك لك ه ا ال حث إي ك ف القيم ال ر ي ل تص يم فق ال ع يير الع ل ي ال ت ع ‪ ,‬م ل أي مي اأن بيب‬ ‫ب ‪ ,‬ك لك إي التص يف م سيب ج‬ ‫سرع ال ي اخل اأن بيب مق نت مع أقل أقص سرع مس‬ ‫غيره من القيم ال ر ي ‪.‬‬ ‫اأن بيب في ال‬ ‫يش ل ال حث أي ً ت طيط تص يم سم ال ق ع الط لي ال‬ ‫‪.‬‬ ‫فق أقل ك م‬ ‫لت طيط تص يم أ م ي أخر‬ ‫جي ل ي عربي تعت ر ن‬ ‫ي ن أ يحت‬ ‫به‬ ‫لك لتق يل‬ ‫اح ض ن غرف الت تيش ال اح‬ ‫بت‬ ‫إ أهم م ي ي ه ا ال حث ه اعت التصريف بأك ر من أن‬ ‫اح يتم اختي ان بين أ أك ر أقل‬ ‫تق يل اقط اأن بيب ال ير ‪ ,‬ف اً ب اً من اختي قطر ك ير أن‬ ‫الح ري‬ ‫قطر م ه ه مي ج ير ب اهت ع ع الرغ في است ا أن بيب ا أقط ك ير أ ع ت فره ‪.‬‬ ‫‪Appendix‬‬ `