mapping of flooding points and rainfall data using … · management of research and technical...

RIO DE JANEIRO CITY HALL MUNICIPALSECRETARY OF SANITATION AND WATER RESOURCES

SMAR WATER SANITATION AND DRAINAGE AUTHORITY - RIOÁGUAS

BOARD OF STUDIES AND PROJECTS

MANAGEMENT OF RESEARCH AND TECHNICAL SUPPORT

MAPPING OF FLOODING POINTS AND RAINFALL

DATA USING ARCGIS

RIO DE JANEIRO CITY - RJ - BRAZIL

2014-2015 RAINY EVENTS

Author:

Nelson Luiz de Andrade Lima Management of Research and Technical Support Board of Studies and Projects – RioÁguas

May 2015





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.





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.





The sources of data:

PDMAP Network (Frequency / Forecast = 5 minutes). RioÁguas Network (Monitoráguas).

Lightnings Detection System (Frequency / Forecast = 3 minutes).

Satellite Images (Frequency / Forecast = 4, 3, 2, 1 day, 6 hours our 30 minutes)





AlertaRio System (pluviographs) (Frequency / Forecast = 15 minutes).

Radar Images (Frequency / Forecast = 2 minutes).





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.

Operational Center RIO (COR-RIO) and Alerta-Rio System.

Operators working in the field (Information sent by radios and mobile phones).





City Topography and Hydrography:

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.

Groups of mountains and lowlands. Runoff and flooding points formations.





The Need for the Mapping:

The proposal to develop a mapping work arose from the need to obtain short and long-

term 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.

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.

Types of cleaning service of the drainage network run by SECONSERVA.





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.

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.

Drainage project development and execution of cleaning services in channels.





Representative scheme of the data collection and departments involved.

PLUVIOGRAPHS

DATA

LOCATION OF

FLOODING POINTS

MAPPING

FIELD DATA

(FLOODING

POINTS)

RAIN DATA

(PLUVIOGRAPHS)

Basic scheme of data extraction and combination.





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)

15 15

30 25

45 35

60 40

90 46

120 51

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.





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

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).

Recurrence time for the drainage devices project.





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:

5) Territorial 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.

LEGENDA

Polygons

INT_MAX_mm_15min

0,400000 - 5,000000

5,000001 - 10,000000

10,000001 - 15,000000

15,000001 - 20,000000

20,000001 - 25,000000

Hidrografia___Rios

Sub_Bacias_Hidrograficas

Limite_de_Bairros





RAINY EVENT MAPPING – JANUARY 16th 2014

Kilometers

LEGEND

Hydrography

Sub Basins

Neighborhoods Limits





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.





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;





- 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);

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.

Application for smartphones in Ios Language / Android / Windows for data and image register of flooding points.

LIMNIMETRIC

RULER





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/2013.

- 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 2010.

- Relatório N.º 4-3-D-001271 - 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/2015.

- Relatório N.º 4-3-D- 001288 - RIO-ÁGUAS/DEP/GPST - ESTUDO PARA ELABORAÇÃO DE

APLICATIVO PARA SMARTFONES EM LINGUAGEM IOS/ANDROID PARA REGISTRO

DE DADOS E IMAGENS REFERENTES AOS BOLSÕES DE ÁGUA - MARÇO/2016.

- Relatório N.º 5-3-D-000417 - 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 2015 - MARÇO/2015

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