Urban Storm Water Management
Project Work: Modelling with PCSWMM
- RESUME……………………………………………………………………………………………………………. 3
- INTRODUCTION………………………………………………………………………………………………… 3
- MOTIVATION…………………………………………………………………………………………………….. 4
- OBJETIVES………………………………………………………………………………………………………… 5
- LAND DESCRIPTION………………………………………………………………………………………….. 6
- SWMM MODELING……………………………………………………………………………………………. 7
- RESULT ANALYSIS………………………………………………………………………………………….. 13
In this work, we pretend to perform an analysis of a drainage system for a given field in two situations, the terrain undeveloped and a developed land were compared. For it, is modeled on the software SWMM with the given boundary conditions and three different designs storm. It aims to highlight the negative impact of urban development on the natural ecological balance. In this paper we will learn to model a proper drainage system in the SWMM as well as the importance of good design of urban drainage. We learn the various parameters used by the program and see the influence in different types of soils.
A drainage system is one whose main function is to allow the withdrawal of the waters that are located on the ground surface, causing inconvenience either agriculture or urban areas or roads.
The source of water can be:
- By runoff.
Mainly, the drainage system comprises a network of channels that collect and lead water elsewhere, outside the area to be drained, preventing the entry of external water. Typically, these systems are necessary in the wide estuaries of large rivers and valleys where natural drainage is poor.
The network of canals or ditches should be periodically cleaned, removing the mud that is deposited in them and weeds growing on the bottom and on slopes, otherwise the water flow would be changed very easily and the system efficiency is lost.
It means urban drainage systems a set of actions, materials or not, designed to avoid, as far as possible drainage, stormwater cause damage to persons or property in the cities or hinder the normal development of life urban.
Within the term ” storm water ” are understood not only caused precipitation falling directly on urbanized areas that make up the population, but also those that precipitate onto other areas, but drift across the city either by natural channels, artificial conduits just along its surface.
It is known the tendency of population displacement from rural to urban areas. That is why the management urban storm water is gaining importance in recent years.
Storm water Management Definition: it refers to a group of techniques used to mitigate the undesirable effects produced by the quantity and quality of urban runoff, known as sustainable urban drainage systems (SUDS) in the UK, the Best Management Practices (GMP) in the US, Water Sensitive Urban Drainage (WSUD) in Australia
The need to address the management of rainwater from a different perspective conventional, combining hydrological, environmental and social aspects, he is beingrapidly increasing worldwide use of sustainable urban drainage systems.
ACTIONS IN URBAN DRAINAGE
The actions that the definition of urban drainage system is concerned, are all measures, material or otherwise, that make up a drainage system. These actions can be of two types: preventive, which reduce damage by proper administration of the uses of urban areas potentially subject to them; and corrective, relieving those you damage in areas where measures of preventive insufficient practical purposes, actions involving the construction of a hydraulic work, or other dimensions and characteristics are not changed for hydraulic reasons, are corrective remaining are considered preventive.
As a result of the above, the most common corrective actions are: regulation and reservoir works; canalization and rectifications natural channels; Driving works , such as canals and pipes; and related issues such as and sinks, sinks, sewers, clarifiers or modifications of sections and plotted on streets and avenues works; and themselves the most common preventive actions shall consist of the conservation and protection of the tributary watersheds, regulating land use, regulation of buildings (such as minimum levels or use of basements and ground floors), the forecast floods; The acquisition of flood-prone areas , education and adequate information of the inhabitants of the city, and regulation of the use of the roads .
As mentioned earlier, migration to the cities has negatively influenced, forcing seek an environmental approach in managing urban drainage.
The urban development alter substantially the hydrology of the basins where it is produced. In particular, the drainage network and the process of rainfall-runoff transformation change. As a result of the urbanizing activity, natural streams that formed the original river system are usually profoundly altered, which directly affects their ability to drain and therefore favors the existence of flooding. Rain runoff transformation is altered as a result of the traditional criterion present in many processes of urbanization: rainwater must be eliminated as efficiently and quickly as possible. This involves avoiding temporary surface retention and infiltration, as well as increase the speed of movement of water into the lower parts of the basin. This dynamic gives the final result which drainage networks such low parts being subject to hydrographs more volume (greater runoff coefficient), higher peak flow and increased sharply (less time between the onset of rain and presentation maximum flow, decreased attention span).
When urban development is from the old center to areas located at higher elevation, the above processes often result in an increase in the flow rate cannot be transported by the existing network of drainage in the old urban area, presenting problems flood. This situation is common in cities located along the coast and have undergone rapid ingrowth.
As we called before, Storm water Management refers to a group of techniques used to mitigate the undesirable effects produced by the quantity and quality of urban runoff, known as sustainable urban drainage systems (SUDS) in the UK, the Best Management Practices (GMP) in the US, Water Sensitive Urban Drainage (WSUD) in Australia
The philosophy of SUDS is to reproduce, as faithfully as possible, the hydrological cycle Natural prior to urbanization or human performance. Its aim is to minimize the impacts of urban development in terms of quantity and quality of runoff (originally, during transport and destination) and maximize the landscape integration and social value and environmental performance of
The objective is to evaluate the efficacy and output response of a drainage system for a typical urban catchment. Also we want to check the increase in runoff due to urbanization and land development, producing a hydrologic imbalance.
Another goal is to monitor an urban drainage system in order to prevent and avoid the dangers of flooding and inundation.
For it, we compare the otuput response by running the model for two conditions, current (land cover is undeveloped, with exising drainage infrastrusture) and future (land use as shown in Figure 1, and with existing drainage infrastructure).
For each of the two conditions, we run the model for 3 different rainfall scenarios: 50mm, 100mm, 200 mm using the SCS 24h Type II design storm.
Another specifc objetives:
- Introduction to modelling with SWMM, procedure for creating, running and analyzing the output of the storm water drainage system model for a typical urban catchment.
- Parameters influencing drainage and drainage network optimization in urban basins
A typical system layout is shown in Figure 1. In this example, the system consists of 7 sub catchment areas (S1-S7) draining to a storm sewer represented by 6 conduits (C1-C6), and 6 manholes (junctions J1-J6), ending at the downstream boundary, Outfall1. We first create the entities shown in the figure, and set the various attributes of these entities.
All drainages are rectangular open channels. Main drainages are 2.5m wide and 1.5 m deep. Smaller drainages are of 1.5 m wide and 1.0 m deep. Adopt an elevation of 106.00 m for the outfall, soil type can be assumed to be clay-loam.
Figure 1: Land description.
In this exercise we will consider two different scenarios, the first to be present, shall consist on the ground undeveloped, and the second consisting of the ground developed and urbanized as can be seen in Figure 1.
Parameters such as soil and waterproofed percentage of permeable and impermeable coefficients soil must be justified by us.
In first place, we must change the general options of the model:
Flow units = CFS | CMS (select CMS)
Routing = Kinematic Wave
Infiltration = Green Ampt
Offsets = Depth (check on the bottom bar menu)
Auto-length = ON (This is VERY IMPORTANT to have on – check on the bottom bar menu)
Now let’s load a background layer for reference before we lay out entities. Click the Map panel tab at the bottom of the screen if the map panel is not already being shown. Click the Open layer button to open the Layer browser. The Layer browser appears and displays background layers previously opened in PCSWMM. Click the Browse button (folder icon) and browse to the required folder which should contain the background image file. Select the image file and click Open. The image should appear.
Now, we can proceed to describe the surfaces of the sub-basins over the map as described in the statement for the assignement, as we can see in the following figure:
To be assigned the option auto-lengh = on the surface of each basin will be assigned automatically.
Next step consists in place the joints with corresponding elevations. We can continue drawing the conduct conecting joints as described in the assignement. The conducs will be rectangular open channels with 2 m high and 5.5 width.
In the drainage channels, first, we will assume concrete drainage channels with a manning value λ = 0.014, depending on the flow velocity we will try natural soil with some vegetation λ = 0.035.
The sub-basins will have a slope between 0.5 and 0.7 %.
The future situation with urban land, the proportion of impervious área will consist in covered areas and pavement. We will Select the percentage of impermeable soil with observation on the map of developed land. Manning coefficient is estimated with reference values suggested by the program, taking the value 0.0135, mediates between rough concrete coating (pavement representative) and brick with cement mortar (representative of the covers), has estimating a storage 1.75mm covers (mean range suggested by the program imperviousness values) while no storage pavement. The roughness coefficient permeable areas (patios and unpaved areas) is chosen as a weighted average surfaces of both types of terrain, with values of 0.13 for unpaved areas and 0.24 for patios; and storage is considered as a weighted average according surfaces, taking as 4 mm values for patios and unpaved areas 3 mm.
For current conditions, soil was found unused, undeveloped. field will consist of clay loam and almost all waterproof floor.
For the infiltration, the selected method is the Green- Ampt. To test the generality of the model application, according to Ogden and Saghafian (1997) 7 soils between 11 USDA textural classification types were selected, from sandy to clay type. Studies Vol.VII Unsaturated Soil Zone. F.J. Samper Calvete and A. Paz González, 2005
The selected parameters for a soild compound for a Clay Loam are:
Wicking = 60 mm
Saturated hydraulic conductivity (Ks) = 2 mm / h
Initial deficit = 0.24
We design the next three different rainfall scenarios according the SCS 24h Type II:
P = 50 mm
P= 100 mm
P= 200 mm
SCS (1973) adopted method similar to DDF to develop dimensionless rainfall temporal patterns called type curves for four different regions in the US.
SCS type curves are in the form of percentage mass (cumulative) curves based on 24-hr rainfall of the desired frequency.
If a single precipitation depth of desired frequency is known, the SCS type curve is rescaled (multiplied by the known number) to get the time distribution.
In the next table we can see the rainfall distribution for SCS 24h Type II.
We obtain the incremental precipitation from the rescaled mass curve to develop the design hyetograph for the different rainfall scenarios, and finally we obtain three differents hyetograph that we will have to introduce in SWMM in time series data.
|SCS 24h Type II||P = 50 mm||P = 100 mm||P = 200 mm|
Table 1: Hyetograph for three differents storms.
If we plot the hyetographs in the same graph we can compare them, as we can see in the next figure.
Figure 3: Chart of the three hyetographs
These values will be introduced in the SWMM at time series data editor to be entered into the rain gauge, will have the following appearance.
Figure 4: Hyetograph plot in SWMM.
Once all the parameters introduced in the model, everything will be ready to run the program.
Before running the simulation, we have to select the measurement interval (15 minuts) and the duration of the analysis (2 days).
Now, we are able to obtain and analyze the results for each scenario and each storm designed. To get a better perspective of the analysis we will obtain the longitudinal profiles of the two joints farther from the outlet (joint 1 and joint 8). also we get the graph of water level and total flow into the otulet for each simulation
For this condition we assume all land is found undeveloped will most land permeable. Following we analyze the results for the three differents storms, P =50 mm, P = 100 mm, P = 200 mm.
Storm P = 50 mm
Figure 5: Profile sheet of wáter from joint 1 to outlet and joint 8 to outlet, current situation, P = 50 mm.
As we can see the depth of water is very small and the maximum depth of water occurs at 13
Figure 6: Water table elvation and flow in outlet, current situation, P = 50 mm.
Storm P = 100 mm
Figure 7: Profile sheet of water from joint 1 to outlet and joint 8 to outlet, current situation, P = 100 mm.
Figure 8: Water table elvation and flow in outlet, current situation, P = 100 mm.
Storm P = 200 mm
Figure 9: Profile sheet of wáter from joint 1 to outlet and joint 8 to outlet, current situation, P = 200 mm.
Figure 10: Water table elvation and flow in outlet, current situation, P = 200 mm.
For the future situation, the land will be urbanized, therefore the percentage of impermeable land will increase. The percentage of impermeable land will be assigned through visual inspection.
Storm P = 50 mm
Figure 11: Profile sheet of wáter from joint 1 to outlet and joint 8 to outlet, future situation, P = 50 mm.
As we can see , the depth of water has increased slightly due to increased imperviousness.
Figure 12: Water table elvation and flow in outlet, future situation, P = 50 mm.
Storm P = 100 mm
Figure 13: Profile sheet of wáter from joint 1 to outlet and joint 8 to outlet, future situation, P = 100 mm.
Figure 14: Water table elvation and flow in outlet, future situation, P = 100 mm.
Storm P = 200 mm
Figure 15: Profile sheet of wáter from joint 1 to outlet and joint 8 to outlet, future situation, P = 200 mm.
Figure 16: Water table elvation and flow in outlet, future situation, P = 200 mm.
For a storm of P = 200 mm in an urbanized land can be seen in the longitudinal profile as the water level has increased significantly, in addition to a higher peak flow and a wáter depth is reached.
This is because the urbanized area makes the soil impermeable and should be captured by the drainage system thus increasing the load.
W.hile it is not urbanized land maintains its initial characteristics of permeability, infiltrating part of the rain on the ground.
Migration to cities and urban development has made it necessary to give more importance to urban drainage management. The need to address the management of rainwater from a different perspective conventional, combining hydrological, environmental and social aspects, he is beingrapidly increasing worldwide use of sustainable urban drainage systems.
The urban development alters substantially the hydrology of the basins where it is produced. In particular, the drainage network and the process of rainfall-runoff transformation change. As a result of the urbanizing activity, natural streams that formed the original river system are usually profoundly altered, which directly affects their ability to drain and therefore favors the existence of flooding. Rain runoff transformation is altered as a result of the traditional criterion present in many processes of urbanization: rainwater must be eliminated as efficiently and quickly as possible.
To check this fact has been carried an analysis of land composed of a drainage system and seven sub-basins. It has been compared with two situations: land undeveloped and developed land.
The results have shown that urban development effectively increases runoff and flow in a given drainage system.
Despite increased runoff, the drafts achieved in the drainage channels are scarce, therefore it concluded that it would be possible are oversized and reduce its section.
In case of it should have produced high runoff, high wáter tables or high speeds, it could have opted to natural soil drainage channels and land with short grass land could emulate the behavior of the natural terrain.
 Anon, (2016). [online] Available at: http://ovacen.com/wpcontent/uploads/2015/05/gestion-del-agua-en-el-planeamiento.pdf [Accessed 8 Jun. 2016]. amper alvete . and arrera am re. . eostatistics pplications to the underground hydrogeology. Barcelona: International Center for Numerical Methods in Engineering.
- (2016). Drainage system (agriculture). [online] Available at: https://en.wikipedia.org/wiki/Drainage_system_(agriculture) [Accessed 8 Jun. 2016].
- (2016). Sustainable drainage system. [online] Available at: https://en.wikipedia.org/wiki/Sustainable_drainage_system [Accessed 8 Jun. 2016].
- Xu, W., Zhang, H., Wang, Z. and Huang, W. (2012). A Study of Manning Coefficient Related With Vegetation Density along the Vegetated Channel. AMM, 212-213, pp.744-747.