MAPPING OF FLOODING POINTS AND RAINFALL DATA USING ARCGIS RIO DE JANEIRO CITY - RJ - BRAZIL RAINY EVENTS

Transcription

1 MAPPING OF FLOODING POINTS AND RAINFALL DATA USING ARCGIS RIO DE JANEIRO CITY - RJ - BRAZIL RAINY EVENTS Author: Nelson Luiz de Andrade Lima Management of Research and Technical Support Board of Studies and Projects RioÁguas May 2015

2 Introduction: During the rainy events in the city the Operational Center RIO (COR-RIO) receives information related to the formation of flooding points that are sent by other municipal departments linked to this system, such as the Municipal Secretary of Conservation and Public Services SECONSERVA, the Rio de Janeiro Traffic Engineering Company - CET-RIO, the Municipal Undersecretary of Civil Defense (SUBDEC) and the Municipal Urban Cleaning Company - COMLURB. Similarly, the ALERTA-RIO system, under the responsibility of the Geotechnical Authority of the Rio de Janeiro City - GEO-RIO, discloses the rainfall data at each event. All these data are then compiled in the form of spreadsheets and sent to the Water Sanitation and Drainage Authority of the Rio de Janeiro RIO-ÁGUAS for disclosure, analysis and for being archived subsequently. RioÁguas has recently acquired the ArcGIS software in order to start to work with Geographic Information Systems (GIS). With this tool it was possible to perform the intersection of hydrological data with those related to the urban drainage system of the city by the geographical mapping of these data. Once these data were available it was took the initiative to aggregate them, so they could be analyzed together. This proposal has driven the development of the present work, which aims to make an assessment of the trends and characteristics related to the formation of drainage points that presented aspects of inefficiency of stormwater runoff along the rainy events throughout the year of 2014, considering its respective georeferenced mapping.

3 The phenomenon of rain: When the water clouds coalesces and forms rain, there is the phenomenon of precipitation which can be associated with different weather phenomena under different scales of spatial and time development. In a general way, there may be three different types of rainfall: - The "frontal rainfalls" that are caused by the meeting of a cold and dry mass with other hot and humid. It comes with the rise of the warm and moist mass of air, than there is a cooling of it that condenses and forms precipitation. They are generally of medium intensity, long duration and reach large areas; - The "convection rainfalls" are also called "summer rains" and are caused by intense evaporation of wet and hot surfaces (such as forests, cities and tropical oceans). The air rises in air parcels that cool off without exchanging heat with the outside environment during its ascent. They are associated with the sea breeze entry in the late afternoon and usually are of great intensity, short duration and reach small areas; - The "orographic rainfall" occurs when moist winds rise and cool off by the meeting with a mountain barrier, as usual on the slopes facing the sea. They are generally of low intensity, high duration and reach small areas. Types of Rain: Convection, Frontal and Orographic.

4 The sources of data: Satellite Images (Frequency / Forecast = 4, 3, 2, 1 day, 6 hours our 30 minutes) Lightnings Detection System (Frequency / Forecast = 3 minutes). PDMAP Network (Frequency / Forecast = 5 minutes). RioÁguas Network (Monitoráguas).

5 Radar Images (Frequency / Forecast = 2 minutes). AlertaRio System (pluviographs) (Frequency / Forecast = 15 minutes).

6 Operators working in the field (Information sent by radios and mobile phones). Operational Center RIO (COR-RIO) and Alerta-Rio System. The Operational Center RIO (COR-RIO) has about 500 digital cameras around the city to give traffic operators an overview of the most important roads and crossroads. The images are displayed on a LCD video wall of 80 m². The information comes from all the participant departments in the system and is placed in layers on a Google map, which allows the visualization of a wide and rapid insight into the workings done the city in real time.

7 City Topography and Hydrography: Groups of mountains and lowlands. Runoff and flooding points formations. The city of Rio de Janeiro has a characteristic relief, presenting three important groups of mountains: Pedra Branca, which crosses the city from east to west, the Gericinó at north and Tijuca or Carioca, at east. There is a high trend to form orographic rainfall around these mountains and because of a steepy relief and areas squeezed between the sea and the mountain the time of concentration for the rain is usually very short which results in a very limited time for the adoption of emergency measures related to the drainage.

8 The Need for the Mapping: The proposal to develop a mapping work arose from the need to obtain short and longterm information. The short-term refers to urgent operational measures to be decided during the rains and the long-term refer to the actions of structural nature to be planned after the rainy event. Due to the limitations of human and material resources that exist in the public service it is necessary to seek out for an optimized service attendance. Thus, field teams need more precise information on the locations where its operations can be more effective. During the rainy events these teams should act quickly and accurately, in order to reduce the impact of problems caused by floods on the population: The Civil Defense needs to know in which places there are intense flooding, where people at risk should be removed; CET-RIO ought to be informed about the roads blocked by the floods, in which shall be carried out the diversion of vehicular traffic; COMLURB urge to be updated about the points where there was accumulation of garbage and where will be the necessity to make a cleaning and SECONSERVA the streets whose drainage network is clogged and needs to be cleaned. Types of cleaning service of the drainage network run by SECONSERVA. The great challenge presented is related to the prediction of possible places subject to floods from the data sources that the city has available, so the operators that work in the field could be send to the places where there must be a greater urgency and need.

9 In the long term can be mentioned the work of dredging and development of projects and execution of drainage works. Criteria could be set to indicate the locations where these services are most necessary. Drainage project development and execution of cleaning services in channels. From the analysis of recorded rainfall data would be possible to try to make a correlation between the magnitude of physical quantities (associated to the rain) and the consequences caused by the phenomenon of rain (formation of floods). RioÁguas then sought to gather this data in a georeferenced mapping, making the appropriate calculations and looking to take the first steps to develop a forecasting system and control of flooding points that could operate in real time. Next is schematically represented, the way how the data were collected for carrying out the mapping with the representation of the departments involved in the process. And yet, how was done the combination of the data used in mapping: in one side the data obtained in the field, rain gauges network.

10 LOCATION OF FLOODING POINTS PLUVIOGRAPHS DATA Representative scheme of the data collection and departments involved. FIELD DATA (FLOODING POINTS) RAIN DATA (PLUVIOGRAPHS) MAPPING Basic scheme of data extraction and combination.

11 Information Mapped Rainfall Intensity - I The amount of rainwater is measured in millimeter (mm). A millimeter index is equal to one liter per squared meter. It is measured by an instrument called rain gauge or pluviometer. The mouth of a funnel with an known area collects the rain drops and accumulate them in a reservoir placed below the funnel. When the changes in time of rainfall record are wanted it is used another type of instrument called a pluviograph, that is nothing more than a rain gauge provided with a continuous chronological record device. It was used as a criterion to consider an intense precipitation the the value of 15mm/15min or 25mm/30min, as the table below DURATION (min.) PRECIPITATION (mm) It is considered that once there is the indication of a rainfall intensity above the maximum permissible the regions that are geographically linked to this index will be susceptible to the occurrence of flooding. Duration of rain - D The time that the rain remains in the precipitation phenomenon. It could be measured in hours or minutes. Recurrence time (Frequency - F) Also known as Time of Return or Time of Recurrence it s the time estimated for the recurrence of a particular event. It is defined as the inverse of the probability of an event to be matched or exceeded. The F unit is usually given in years.

12 It is very useful for risk analysis and design of engineering works, usually with the aim of minimizing the harmful effects of certain natural phenomenon. The time of recurrence or payback period to be adopted in the design flow and drainage design of the devices should be considered as shown below: Type drainage device Time of recurrence T (years) Microdrainage - storm sewer 10 Macrodrainage - uncoated channels 10 Macrodrainage - coated channels 25 Recurrence time for the drainage devices project. The event recurrence time is obtained from the rain intensity and duration applied to IDF curves. If the RT of the event is lower than the RT of the design the designed system is expected to operate properly. Representative IDF curve of one of the 33 pluviographs (Botanical Garden).

13 Nature of Reference Data The data that were used as reference for the analysis were selected according to the three most relevant information related to the precipitation of rain are intensity, duration and frequency of the rainfall event, also considering its geographical position along the various neighborhoods of the city. Data Mapping After the acquisition of ArcGis program a training course for the use of the tool was offered to RioÁguas technical team. With just the knowledge of some basic resources it was possible to perform the mapping of the presented information. From the reports sent by COR-RIO, with the location of flooding points reported by the departments linked to the network, a georeferenced mapping was performed. This mapping with visual information considers the following: 1) Rivers Network (rivers and canals) with its proper description. 2) Delimitation of sub-basins associated with the main rivers of the network. 3) Territorial distribution of rainfall indexes in blue color (maximum intensity in mm/15min), considering the area of influence of each of the gauges and their precipitation rates. 4) Mapping by color grid associated to the rainfall rates (maximum intensity in mm/15min), considering the following color scale: 0, , , , , , , , , , ) Territorial Hidrografia Rios distribution of rainfall recurrence times (in purple) and total duration (in green), by each rain gauge. 6) Mapping of flooding points formation (made by balloons with stars marking). 7) Mapping of drainage points already supervised.

14 RAINY EVENT MAPPING JANUARY 16th 2014 LEGEND Kilometers Hydrography Sub Basins Neighborhoods Limits

15 Obtained information with mapping The visualization of data distribution and calculations and statistical analysis performed allowed to do some observations from the superposition of the considered input data: - It has been found the formation of flooding points in places with lower precipitation rates than established by the alert criteria (15mm/15min or 25mm/30min); - There were points at which the intensity of rain could have been considered high, according to the warning criteria, but which nevertheless has not detected any failure of the drainage system at a single point; - Flooding points were formed in places assisted by storm sewer even with event s RT smaller than 10 years and close to channels with event s RT smaller than 25 years; - The occurrence of floods is associated with rainfall that is distributed throughout the territory of the city, but with an average intensity below the warning criteria of the index; - Definition of rain gauges whose areas of influence were forming more points of flood; - Onset of flooding points that have never been mapped before and frequency index for each point; - Indication of the rainfalls associated with each of the flooding points formed; The information obtained from the mapping indicates that the criteria used to define an alert under the geotechnical viewpoint, should not be the same as those set considering the aspect of drainage, despite the fact that they both use information from the same network of rain gauges. It is necessary therefore to establish proper indexes for the drainage system, which may be obtained from the mapping.

16 Future implementations in georeferenced system The model developed still lies in a primary stage and need to pass through future implementations that may make it more sophisticated and accurate, being necessary for such a large number of input data and calibration of the model. As an example of these implementations the inclusion of the following aspects in the modelling can be mentioned: - Use mapping with digital elevation model processed by INPE and TOPODATA; - Inclusion of altimetry considering a three-dimensional mapping of the relief and hydraulic data associated with rivers and channels; - Definition of the flow direction of rivers and channels; - Definition of runoff coefficients (runoff) from the land use map; - Inclusion of the implanted drainage network (as built); - Direct linking of rainfall data to the contribution basins of the rivers and channels; - Incorporation of tidal influence in the flow of rivers and channels that disembogue near the shore; - Inclusion of the information available from the monitoring system of the RIO-ÁGUAS hydrometric network; - Inclusion of information concerning the extension of each flood point; - Inclusion of the data related to temperature, relative humidity and wind speed in the period that immediately preceds each rainy event; - Conduct hydrologic analysis with Spatial Analyst; - Integration between archiving systems: SISARQ, SigÁguas and Geovias; - Indication of alternate routes of traffic from the points where floods were mapped; - Drainage Network Extraction, Algebra maps and Watershed Delimitation;

17 - developing an application that allows the field teams of technicians to communicate with the operational center and make real-time mapping of flooding points (using the Collector); LIMNIMETRIC RULER Application for smartphones in Ios Language / Android / Windows for data and image register of flooding points. It can be considered that the completion of the mapping process of flooding points was only a first step towards the implementation of a more complete georeferenced system, for which the adoption of an ongoing effort to improve is required by including improvements in the system, so that it will possible in a near future to obtain more accurate data related to rainfall and hydraulic flow. The goal will be to evolve the system to a level in which the development of a real-time simulation forecasting of hydrological scenarios, based on data obtained from the data network, can be possible.

18 References - INSTRUÇÕES TÉCNICAS PARA ELABORAÇÃO DE ESTUDOS HIDROLÓGICOS E DIMENSIONAMENTO HIDRÁULICO DE SISTEMAS DE DRENAGEM URBANA (Aprovada pela Portaria O/SUB RIO-ÁGUAS N nº. 004/2010). - INFORMAÇÕES NECESSÁRIAS PARA PROCEDIMENTOS DE AÇÃO NOS ESTÁGIOS DE ALERTA DE CHUVA EMITIDOS PELO COR-RIO - FEVEREIRO/ INSTRUÇÕES TÉCNICAS PARA ELABORAÇÃO DE ESTUDOS HIDROLÓGICOS E DIMENSIONAMENTO HIDRÁULICO DE SISTEMAS DE DRENAGEM URBANA (Aprovada pela Portaria O/SUB RIO-ÁGUAS N nº. 004/2010) - 1ª. Versão - Dezembro Relatório N.º 4-3-D RIO-ÁGUAS/DEP/GPST - ESTUDO PARA IMPLANTAÇÃO DE UM SISTEMA DE RÉGUAS LINIMÉTRICAS PARA MEDIÇÃO DE LÂMINAS D ÁGUA NOS PONTOS DE DRENAGEM SUPERVISIONADOS - OUTUBRO/ Relatório N.º 4-3-D RIO-ÁGUAS/DEP/GPST - ESTUDO PARA ELABORAÇÃO DE APLICATIVO PARA TFONES EM LINGUAGEM IOS/ANDROID PARA REGISTRO DE DADOS E IMAGENS REFERENTES AOS BOLSÕES DE ÁGUA - MARÇO/ Relatório N.º 5-3-D RIO-ÁGUAS/DEP/CGPM - AVALIAÇÃO DOS PONTOS DE DRENAGEM REPORTADOS PELOS ÓRGÃOS VINCULADOS AO COR-RIO E MAPEAMENTO EM SISTEMA GEORREFERENCIADO (ARCGIS) - EVENTOS CHUVOSOS NO ANO DE MARÇO/2015