+ All Categories
Home > Documents > 2015 / 2016 Flood risk analysis - ULisboa · 2015 / 2016 Flood risk analysis . Flood cost IST:...

2015 / 2016 Flood risk analysis - ULisboa · 2015 / 2016 Flood risk analysis . Flood cost IST:...

Date post: 30-Nov-2018
Category:
Upload: phamngoc
View: 222 times
Download: 0 times
Share this document with a friend
85
Rodrigo Proença de Oliveira Hydrology, environment and water resources 2015 / 2016 Flood risk analysis
Transcript

Rodrigo Proença de Oliveira

Hydrology, environment and water resources 2015 / 2016

Flood risk analysis

Flood cost

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 2 17-11-2015

Spatial distribution

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 3 17-11-2015

Flood losses

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 4

99 vitimas por ano

17-11-2015

Lisbon area, November 1967 110 mm / 5 hours: 700 deaths and 1000 loss their homes

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 5 17-11-2015

Lisbon area, November 1983

10 deaths e 200 families lost their homes

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 6 17-11-2015

Madeira, February 2010

42 deaths

7 IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 17-11-2015

Madeira, February 2010

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 8 17-11-2015

Madeira, February 2010

9 IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 17-11-2015

Madeira, February 2010

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 10

EARAM study (IST) results

17-11-2015

Lower Tagus flood, April 2013

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 11 17-11-2015

New Orleans, 2005 (Katrina hurricains)

1000 deaths, one million lost their homes

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 12 17-11-2015

Flood control

(flood risk reduction)

• Clearance of flood prone areas

/ Deslocação de pessoas e bens

de áreas com uma probabilidade

elevada de ocorrência de

inundações;

• River works to increase the

cross-section area / Melhoramento das secções dos

cursos de água para aumento da

sua capacidade de vazão;

• Building of dikes to increase

the cross-section area / Construções de diques para

aumento da secção de vazão;

• Use of reservoirs for flood

atenuation / Atribuição de um

volume de encaixe de cheias para

atenuação do hidrograma de

cheia;

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 13

Caudal afluente, Qa Caudal efluente, Qe

17-11-2015

Dikes in lower Tejo

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 14 17-11-2015

Mississipi 1927 130,000 homes lost; 700,000 people were displaced. 246

deaths; million 350 dollars of Property damage (5 billion dollars today)

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 15

Flood control act of 1928 and the Room for the river

project and the 2011 flood event

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 16

2011: • No deaths

• 21.000 homes and business impacted

• 2,8 billions USD losses

Scenario without the MRTSystem • 1,5 billions of homes and business impacted

• 238 billions USD losses

Holanda, Rhine

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 17 17-11-2015

Projecto Room for the river (Holanda)

• Dar espaço ao rio Reno / Room for

the river;

• Objectivos / Objectives:

– Reduzir o risco de cheias;

– Melhorar a qualidade da água.

• Metas / Targets:

– Até 2015: Assegurar uma

capacidade de escoamento de

16’000 m3/s;

– Até 2020: Reduzir os níveis

máximos de cheia em 70 cm.

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 18

Projecto Room for the river (Holanda)

19 IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015

• Medidas / Actions:

– Remoção de obstáculos / removal of flow obstacules;

– Rebaixamento e alargamento do leito / channel dredging ;

– Afastamento de diques / Dikes removals ;

– Remoção de polders / Polders removal;

– Melhoria do dique (casos pontuais) / Dikes improvement;

Custo:

2.1 biliões de euros.

17-11-2015

Exemplo: Room for the river (Holanda)

Plano base: 2015

20 IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015

Flood analysis

Factors influencing flood risk

• Watershed area / Área

• Watershed shape / Forma

• Watershed orography / Relevo

• River network / Rede hidrográfica

• Soils / Solos

• Soil cover / Coberto vegetal

• Soil use / Uso da superficie

• Precipitation temporal distribution / Distribuição temporal da precipitação

• Temperature / Temperatura

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 22

Time for flow accumulation (concentration

time ands isochrones)

Tempo para acumulação do escoamento (tempo

de concentração / isócronas)

Infiltration

Infiltração

Factor Influences

Less important

Menos importante

17-11-2015

Flood hydrograph

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 23

Caudal, Q

Tempo, t

Escoamento total

Escoamento directo

Escoamento de base

Precipitação, P

Tempo de ascenção

Precipitação

útil

Intercepção, retenção

e infiltração

Tempo de decrescimento

Total flow

Direct flow

Base flow

Net precipitation

Interception, retention and infiltration

Rising time Decreasing time

Discharge

Q

Time, t

17-11-2015

Main parameters or variables that are usually

estimated

It depends on the purpose of the analysis: – Preliminary risk assessment / Avaliação preliminar do risco

de cheia

– Spillways design / Dimensionamento de descarregadores

– Bridge design / Dimensionamento de pontes

– Dikes design / Dimensionamento de diques

– Storm water drains design / Dimensionamento de colectores

– Design of flood attenuation storage volume / Dimensionamento de volumes de encaixe de cheia

– Flood damage evaluation studies / Avaliação da duração da

cheia e dos prejuizos causados

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 24

Time

Discharge

Flood volume Volume de cheia

Peak discharge Caudal de ponta

Flood peak / Caudal máximo

(ponta de cheia)

Flood peak / Caudal máximo

(ponta de cheia)

Flood volume / Volume de cheia

17-11-2015

Water balance simplification

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 25

Escoamento

superficial

(directo)

Escoamento

de base

Evapotranspiração

Intercepção

Retenção

Evaporação

Infiltração

Precipitação

Recarga

Escoamento

intermédio

Evaporação

Precipitação

P = H + E + Sp + Ss + Su + Ex – R

For a short time interval / Para um

intervalo de tempo curto:

E = 0 (evapotranspiration)

Su = 0 (aquíier contribution)

Ex – R = 0 (export-import)

Logo, H = P - Sp - Ss

Se Su <> 0

Logo, H = P - Sp - Ss + Su

Considered in a simplified way

Considerado de forma simplificada

Considered in a simplified way

Considerado de forma simplificada

17-11-2015

Opções para pequenas bacias hidrográficas

Assumptions for small watersheds analysis

Possible assumptions on hydrological fluxes during

a flood / Possíveis simplificações na análise dos fluxos

hidrológicos durante uma cheia:

• Evaporation and evapotranspiration: Often

ignored/ Evaporação + evapotranspiração: São

frequemente desprezadas na análise de situação de cheia

• Retention, interception and infiltration

(“losses”): A simple model is used / Retenção,

intercepção, infiltração (“perdas”) / Assume-se um modelo

simples:

• Intermediate flow: Often ignored / Escoamento

intermédio Frequentemente desprezado;

• Base flow: Often ignored or estimated using a

simple model independent from infiltration

estimate. / Escoamento de base: Por vezes ignorado ou

calculado com base num modelo simples e independente da

infiltração.

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 26 17-11-2015

Precipitação, P

Precipitação, P

Loss models: Constant infiltration / Taxa

constante;

Initial loss + Constant infiltration

/ Volume inicial + taxa constante;

Isochrones and time of

concentration

Isochrones

Consider a rainfall event with a

duration equal to the double of the

time of concentration

Chuvada com uma duração da precipitação

útil igual ao dobro do tempo de

concentração da bacia hidrográfica

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 28

Time Tempo

Areas contributing to flow Áreas que contribuem para o

escoamento

0 0

1/3 x tc A

2/3 x tc A + B

tc A + B + C

4/3 x tc A + B + C

5/3 x tc A + B + C

2 x tc A + B + C

7/3 x tc B + C

8/3 x tc C

3 x tc 0

A

BC

Isócrona 1/3 x tc

Isócrona 2/3 x tc

Ponto mais

afastado

17-11-2015

Time of concentration

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 29

Assuming the precipitation falls uniformly over the

whole watershed (valid for small watersheds) Assumindo que a precipitação se distribui de forma

uniforme em toda a bacia hidrográfica (válido em

pequenas bacias).

17-11-2015

Discharge, Q

Time, t

Total flow

Direct flow

Base flow

Precipitation, P

Rising time

Net

precipitation

Interception,

infiltration

Falling time

Time of concentration

Discharge, Q

Tempo, t

Direct flow

Net precipitation, Pu

Time of concentration

Time of concentration

• Travel time from the most distant point to the watershed

outflow section / Tempo de percurso de uma gota de água entre o ponto

cinematicamente mais afastado da secção da bacia e a secção definidora da bacia;

• We assume it is an intrinsic characteristic of the

watershed; Propriedade intrínseca da bacia hidrográfica / Assume-se que é independente da precipitação, dependendo apenas das condições de

escoamento desde o ponto mais afastado até à secção final;

• Depends on the watershed characteristics / Na prática assume-se

que depende das características da bacia hidrográfica:

– Watershed area / Área da bacia (A);

– Length of the main watercourse / Comprimento do curso de água principal (L);

– Watershed average heigth / Altura média da bacia (hm);

– Slope of the main watercourse /Declive médio do curso de água principal (dm);

– Altitude difference along the main watercourse /Diferença de cotas do

talvegue do curso de água principal (H);

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 30 17-11-2015

Time of concentration estimation methods

• Analysis of observed hyetographs and hydrographs / Análise

dos hietogramas e hidrogramas observados;

• Cinematic computation based on distance travelled and

water velocity estimation / Cálculo cinemático: Cálculo do tempo de

escoamento do ponto cinematicamente mais afastado até à secção de referência,

aplicando por exemplo a fórmula de Manning-Strickler tendo em conta as condições de

escoamento ao longo das encostas e nos cursos de água de ordem crescente;

• Empirical formulas (for small watersheds) / Fórmulas empíricas

(para pequenas bacias hidrográficas):

– Giandotti:

– Temez:

– Kirpich (segundo Chow):

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 31

m

ch

LAt

8,0

5,14

76,0

25,03,0

m

cd

Lt

385,0

155,1

95,0H

Ltc

• tc (h) – Time of concentration

• A (km2) – Area of watershed

• L (km) – Length of main river

• hm (m) – Avg heigth of watersh

• dm (-) – Avg slope of main river

• H (m) – Altitude difference along main river

17-11-2015

Exercise

A net precipitation with intensity IA, IB, IC and ID occurred in each of the areas of

the represented watershed. The following table presents such distribution with I0

representing a reference intensity and tc the time of concentration of the

watershed. Determine the direct flow hydrograph resulting from such

precipitation in I0xA0 units. Em cada uma das zonas da bacia hidrográfica representada ocorreu precipitação útil de acordo com as

intensidades IA, IB, IC e ID que se apresentam no quadro seguinte, onde I0 representa uma intensidade de

referência e tc, o tempo de concentração da bacia hidrográfica. Determine o hidrograma do caudal do

escoamento directo resultante de tal precipitação, em unidades de I0 A0.

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 32

t/(tc/4) (-) 0 - 1 1 - 2 2 - 3 3 - 4 4 - 5

IA/I0 (-) 0.0 0.0 0.0 0.5 0.0

IB/I0 (-) 0.0 0.0 0.5 0.5 0.0

IC/I0 (-) 0.0 0.5 0.5 0.0 0.0

ID/I0 (-) 1.0 0.5 0.0 0.0 0.0

17-11-2015

Exercise

In particular river basin, with 290 km2, in prolonged periods without rainfall, the

flow rate in the reference section follows the following law / Em determinada bacia

hidrográfica, com 290 km2, em períodos prolongados sem precipitação, o caudal na secção

de referência segue com bastante aproximação uma lei de esgotamento do tipo.

Knowing that at 9 am of March 4 and March 13 the flow rate at the outlet of this

basin was respectively 10.9 and 7.3 m3/s and assuming that no precipitation

occurred between these two dates, estimate the volume of water that has passed

through the outlet from the latter date until full depletion of the basin. Express

this volume in water height evenly distributed over the basin / Sabendo que nessa

bacia hidrográfica, às 9 horas de 4 de Março e de 13 de Março o caudal era respectivamente

de 10,9 e 7,3 m3/s e admitindo que não ocorreu precipitação, estime o volume de água que

passou na secção de referência desde a última data até ao total esgotamento da bacia.

Exprima esse volume em altura de água uniformemente distribuída sobre a bacia.

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 33

)tt(k0

0eQQ

17-11-2015

Empirical formulas for peak

discharge estimation

Empirical formulas

• Iskowski (1886)

• Giandotti

• Soil Conservation Service

• Mockus

• Meyer

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 35

APmKQ Not a function of the return period

ct

h

AQ

pt

hk

A277,0Q

cc tt

hk

6,0

A277,0Q

ct2

Q – Peak flow (m3/s)

A – Watershed area (km2 )

h – Event precipitation (mm)

k – Peak factor in the range of 1 and 0,5

tp – Peak time = 0,5 D + 0,6 Tc

D – Duration of precipitation

Assumes a critical precipitation duration of

αACQ

Q – Peak flow (m3/s)

K – Coeficient dependent on soil type, land cover and orography

m – Coeficient dependent on the area of the watershed

P – Average annual precipitation (m)

A – Watershed area (km2)

Q – Peak flow (m3/s)

A – Watershed area (km2)

Tc – Time of concentration

– Coeficient dependent on the area of the watershed

h – Precipitation (mm)

Q – Peak discharge; (m3/s)

C – Coeficient dependent on the watershed characteristics and return period;

a –Coeficient dependent on the watershed characteristics (0.4 < a < 0.8)

A –Watershed area (km2)

17-11-2015

Rational formula

• C –Coeficient dependent on the watershed characteristics and return period / Coeficiente dependente das características da bacia (tipo de solo e uso do solo) e do período de retorno:

– C smaller for permeable soils and LU and larger watersheds / C menor para solos e uso de

solos mais permeáveis; bacias maiores;

– C greater for impervious soils and LU and higher return periods / C maior para solos e uso de

solos menos permeáveis; maiores períodos de retorno;

• i –Precipitation intensity / Intensidade de precipitação;

• A –Watershed area / Área da bacia;

• f - Majoration coeficient to consider non-uniform precipitation events / Factor de

majoração para considerar distribuições não uniformes da precipitação;

• n –Exponent of the rain depth-duration-frequency curve / Expoente da curva de

possibilidade udométrica;

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 36

nf 2

ntaP AiCQ

AiCfQ A

Precipitation rate, i

Peak

discharge

Q = C i A

17-11-2015

Linear reservoirs

Linear reservoirs:

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 37

𝒅𝑺

𝒅𝒕= 𝑰 − 𝑶

𝑶 = 𝒌 ∙ 𝑺

Inflow, I

Outflow, O

Storage, S

Outflow, O

Storage, S

𝒅𝑺

𝒅𝒕= 𝑰 − 𝒌 ∙ 𝑺

𝒊𝒇 𝑰 = 𝟎 𝒕𝒉𝒆𝒏 𝑺 = 𝑺𝒐 ∙ 𝒆−𝒌∙𝒕

S

t

Inflow, I

Outflow, O

Storage, S

Delay or lag

Attenuation

17-11-2015

Factor C

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 38 17-11-2015

Chow et al, 1988

Department of Water Affairs and

Forestry, Africa do Sul

What is the critical precipitation duration ?

Assuming that the precipitation falls uniformly

over the whole watershed (valid for small

watersheds):

• A small increase of the precipitation duration

leads to an increase in the area of the

watershed contributing to the flow at the

outlet;

• When the duration is higher than the time of

concentration there is an instant where the

whole watershed contributes to the flow at

the outlet;

• An increase of the duration of the

precipitation event leads to a reduction in

the average precipitation rate for a given

probability (return period);

• Therefore, precipitation events with

durations close to the time of concentrations

are the ones that lead to higher peak flows.

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 39 17-11-2015

Exercise

Use the rational formula to determine the peak flow associated with a

return period of 100 years from a watershed with 80 km2 and a time of

concentration of 2.5 h. Assume that 15% of the precipitation is lost to

infiltration and there is a peak flow attenuation through the watershed of

20%. Assume the following precipitation-duration curve, with P in mm and

t in min:

Utilize a fórmula racional para estimar o caudal de ponta de cheia associado a um

periodo de retorno de 100 anos, gerado numa bacia hidrográfica com 80 km2 de

área e 2,5 h de tempo de concentração. Assuma que 15% da precipitação é

perdida por infilitração e que há uma atenuação do caudal de ponta de cheia de

20%. Assuma que a linha de possibilidade udométrica para esse período de

retorno, com P em mm e t em min, é

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 40 17-11-2015

45,0t4P

45,0t4P

C = 0.8 x 0.85 = 0,68

D = tc = 2,5 h = 150 min

P = 4 x 150 0.45 = 38 mm

i = P / D = 15 mm/h

Q = C x i x A = 0,68 x 15 x 10-3 / 3600 x 80 x 106 = 230 m3/s

Exercise

Use the Temez formula and the rational formula to determine the peak

flow for T = 100 years of a rural watershed with 80 km2, where the

main river has 8 km and an average slope 0f 0.005. Assume the

following precipitation-duration curve for T=100 years, with P in mm

and t in min, is:

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 41

45,0t4P

17-11-2015

Exercise

Compute the design flow of an infra-structure whose functionality should

not be affected more 10 times in a century. The watershed of the infra-

structure has an area of 40 km2 and its main water course flows along 4 km

with an average steepness of 0.002. Use the Temez equation and the

rational formula with correcting factor, assuming a C coeficient of 0,5. The

watershed lies within a region with the following Precipitation Depth-

Duration-Frequency curve (P in mm and D in min).

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 42

D (h) T=10 T=50 T=100 T=500

a n a n a n a n

0,5 h – 6 h 37.837 0.398 50.233 0.368 55.673 0.360 67.615 0.344

6 h – 48 h 33.867 0.473 41.092 0.501 44.068 0.509 51.207 0.523

17-11-2015

Exercise

During a rainfall event, the flow capacity of a spillway, estimated in 120 m3/s,

was almost exceeded. The watershed of that spillway na área of 60 km2 and its

main waterscourse flows along 10 km, with an average steepness of 0.0008. The

watershed lies within a region with the following IDF curve (i em mm/h e D em

min). Compute the order of magnitude of the return period of the rainfall event,

using the rational formula and the Kirpich formula. Assume a C coeficient of 0,5.

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 43

t (min) T=10 T=50 T=100 T=500

a b a b a b a b

5 min – 30 min 567 -0,665 742 -0,652 815 -0,649 987 -0,643

30 min – 6 h 445 -0,602 668 -0.632 765 -0.640 992 -0.656

6 h – 48 h 293 -0,527 317 -0.499 329 -0.491 361 -0.477

17-11-2015

Exercise

A linear reservoir with a constant k = 15x10-6 s-1, has at a certain moment a

volume of water V0 = 105 m3. From that moment onwards the inflow is

represented by the hydrograph presented in the table is below, Determine the

hydrograph of the reservoir outflow (Q) from the starting time up to 18 h later

and plot the two hydrographs (I and Q).

Um reservatório linear, com uma constante k=15x10-6 s-1, apresenta em determinado

instante um volume de água V0=105 m3. Sabendo que a partir desse instante foi alimentado

de acordo com o hidrograma que se apresenta no quadro que se encontra abaixo,

determine o hidrograma do caudal saído do reservatório (Q) desde o instante inicial até 18

h depois e represente graficamente os dois hidrogramas (I e Q).

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 44

t (h) 0 1 2 3 4 5 6 7

I (m3/s) 0 14 20 30 46 28 12 0

17-11-2015

Unit hydrograph

The concept of unit hydrograph

• Provides the relationship between the

flood hydrograph and the originating

precipitation / Relaciona a resposta da bacia

(hidrograma de cheia) com a precipitação que

lhe deu origem;

• We assume it is an intrinsic characteristic

of the watershed / It is the hydrograph

produced by a unit net precipitation that fall

during a certain duration;

• Assume-se que é uma propriedade

íntriseca da bacia, independente da

precipitação / É o hidrograma resultante de

uma chuvada de um valor unitário de

precipitação útil e com uma determinada

duração;

• Each unit hydrograph is associated with a

given duration / Está associado a uma

determinada duração da chuvada. IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 46 17-11-2015

Caudal, Q

Precipitação, P

1

How to apply the unit hydrograph (Additivity and proportionalities principles)

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 47 17-11-2015

0 1 2 3 4 5 6 7 8 Tempo / dt

q, u / umax

1

1

Precipitação útil (mm)

2

dt dt

Hidrograma unitário

para uma duração dt

0 1 2 3 4 5 6 7 8 Tempo / dt

q, u / umax

1

1

Precipitação útil (mm)

2

dt dt

Hidrograma unitário

para uma duração dt

Unit hydrograph for

a duration dt

Unit hydrograph for

a duration dt

Net precipitation (mm) Net precipitation (mm)

Application of the unit hydrograph

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 48 17-11-2015

0

.

8

447

34436

2433425

142332414

1322313

12212

111

q

Puuq

PuuPuuq

PuuPuuPuuq

PuuPuuPuuPuuq

PuuPuuPuuq

PuuPuuq

Puuq

4321 ,,, PuPuPuPu

0,,,,,0 543210 uuuuuu

0 1 2 3 4 5 6 7 8

Unit hydrograph characteristics

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 49 17-11-2015

Tc

Precipitation of 1 unit

ocurring in t

Unit hydrograph for

a duration of t

t

Corresponds to a precipitation

intensity of 1/t

The volume of the unit hydrograoh is equal

to 1 x A, where A is the watershed area.

When discretized in t

intervals, it has Tc/T values

that are different from 0.

mm

min

min

(m3/s)/mm

Synthetic unit hydrographs

How to estimate a unit hydrograph

• The UH can be estimated from / O hidrograma

unitário pode ser estimado:

– Observed records from previous

precipitation events (hyetographs and

hydrographs) / A partir de registos observados

de precipitação (hietograma) e de caudal

(hidrograma) de um evento de cheia;

– From watershed characteristics using

synthetic unit hydrographs proposed by

different authors / A partir das características

da bacia – Hidrograma unitário sintético.

• Different authors have proposed synthetic unit

hydrographs / Vários autores avançaram com várias

propostas de hidrogramas unitários sintéticos:

– Giandotti

– Clark;

– Snyder;

– Soil Conservation Service;

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 51 17-11-2015

0 1 2 3 4 5 6 7 8 Tempo / dt

u / umax

1

1

Precipitação útil (mm)

(D + tc) / dt

ta / dt

D = dt

.

Giandotti unit hydrograph

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 52

Hidrograma de Giandotti

t

Q

ta tbtc tt

Qmax

Qmed

t

medt

APψQ

medmax QρQ

ct tγt

ca tρ

1ρt

cb tρ

ρ1)(γt

17-11-2015

A

(km2)

(-)

(-)

(-)

(-)

]0, 300] 10 4.0 0.50 1.25

]300, 500] 8 4.0 0.50 1.00

]500, 1000] 8 4.5 0.40 0.71

]1000, 8000] 6 5.0 0.30 0.36

]8000, 20000] 6 5.5 0.25 0.27

]20000, 70000] 6 6.0 0.20 0.20

Quintela aconselha que se adopte para A < 500 km2

= 6.5

= 4.0

= 0.50

O que corresponde a C = = 0.81

Snyder unit hydrograph

• Parâmetros:

– Lag (h), Tp

– Peak Coeficient, Cp

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 53

Mais informação em HEC-HMS Technical

Reference Manual, Cap. 6

Lag, Tp

Up

Caudal

Tempo

p

pp

T

C

A

U72,2

ccp TTT 75,05,0

17-11-2015

Clark unit hydrograph

• Parameters:

– Time of concentrarion (h), Tc

– Storage coeficient (h), R

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 54

More information in HEC-HMS Technical

Reference Manual, Cap. 6

Diagrama

tempo-área

Reservatório

fictício

tc

Área

Tempo de escoamento

para a secção de refência

17-11-2015

SCS unit hydrograph

• Parameters: Lag (h), Tlag

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 55

See more in HEC-HMS Technical

Reference Manual, Cap. 6

Lag, Tlag

Up

Caudal

Tempo

D

p

pT

AU 08.2

clag TT 6,0

lagp TD

T 2

17-11-2015

SCS triangular unit hydrograph

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 56

0

1

2

Pre

cip

ita

çã

o ú

til (m

m)

0

0.2

0.4

0.6

0.8

1

1.2

0 1 2 3

Tempo / ta

u /

um

ax

2

Dt0.6t ca

ab t3

5t

?Dttt bac a

maxt

A0.208u

ta tb 17-11-2015

Exercise

A continuous and constant net precipitation of 60 mm/h over a given watershed

generates the following hydrograph of direct flow. Please estimate:

– Time of concentration of the watershed.

– Area of the watershed.

– Unit hydrograph of the water for 0.25 h. Em determinada bacia hidrográfica, em resultado de uma precipitação útil com grande duração e

intensidade constante de 60 mm/h, obteve-se o hidrograma do escoamento directo indicado no quadro.

– Determine a área da bacia hidrográfica.

– Determine o hidrograma unitário para a duração de 0.25 h.

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 57

t (h) 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 …

Qd (m3/s) 0 60 150 280 320 340 350 350 …

17-11-2015

Exercise

A precipitation event with a duration of 1,5 h and net precipitation amounts of

5 mm, 10 mm and 3 mm in 3 successive 0.5h time periods over a given

watershed, generates the following hydrograph of direct flow. Please estimate:

– Time of concentration of the watershed.

– Unit hydrograph of the water for 0.5 h.

– Area of the watershed. Em determinada bacia hidrográfica, em resultado de precipitação útil que de 30 min em 30 min foi 5

mm, 10 mm e 3 mm, obteve-se o seguinte hidrograma do escoamento directo.

– Determine o tempo de concentração da bacia.

– Determine o hidrograma unitário para a duração de 0,5 h.

– Calcule a área da bacia, em km2.

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 58

t (h) 0,0 0,5 1,0 1,5 2,0 2,5 3,0

Qd (m3/s) 0 15 70 99 44 6 0

17-11-2015

Exercise

A precipitation event with a duration of 0,5 h and net precipitation amounts of

15 mm and 5 mm in 2 successive 0,25h time periods, generates the following

hydrograph of direct flow. Please estimate the unit hydrograph of the water for

0.5 h. Em determinada bacia hidrográfica, em resultado de uma precipitação útil de 15 mm em 15 min e de 5

mm nos 15 min seguintes, obteve-se o seguinte hidrograma do escoamento directo. Determine o

hidrograma unitário para a duração de 30 min.

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 59

t (h) 0.00 0.25 0.50 0.75 1.00 1.25 1.50

Qd (m3/s) 0 150 275 225 125 25 0

17-11-2015

Exercise

The table presents the unit hydrograph of a given watershed for unit hyetograph

with a duration of 0,5h. Please estimate:

– Time of concentration of the watershed.

– Area of the watershed.

– The direct hydrograph generated by an event with a net precipitation of

20 mm, 30 mm e 12 mm, in 3 successive intervals of 30 min.

– Unit hydrograph of the water for 1 h. Apresenta-se no quadro seguinte o hidrograma unitário de determinada bacia hidrográfica para a

precipitação útil com a duração de 0.5 h.

– Determine o tempo de concentração da bacia hidrográfica.

– Determine a área da bacia hidrográfica.

– Calcule o hidrograma do escoamento directo que resultaria na secção de referência dessa bacia

hidrográfica de uma precipitação útil de 20 mm, 30 mm e 12 mm, em intervalos sucessivos de 30

min.

– Calcule o HU para uma duração de 1 hora.

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 60

t (h) 0.0 0.5 1.0 1.5 2.0 2.5

u (m3/s/mm) 0 15 34 17 9 0

17-11-2015

Design hyetograph

What is the critical precipitation duration ?

Assuming that the precipitation falls uniformly

over the whole watershed (valid for small

watersheds):

• A small increase of the precipitation duration

leads to an increase in the area of the

watershed contributing to the flow at the

outlet;

• When the duration is higher than the time of

concentration there is an instant where the

whole watershed contributes to the flow at

the outlet;

• An increase of the duration of the

precipitation event leads to a reduction in

the average precipitation rate for a given

probability (return period);

• Therefore, precipitation events with

durations close to the time of concentrations

are the ones that lead to higher peak flows.

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 62 17-11-2015

Design hyetograph:

How to arrange the precipitation blocks?

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 63 17-11-2015

Q1=Pu1∙u1Q2=Pu2∙u1+Pu1∙u2

Q3=Pu3∙u1+Pu2∙u2+Pu1∙u3

….

• To maximize a given Qi:

– Multiply the largest u by the largest Pu;

– Multiply the 2nd largest u by the 2nd largest

Pu;

– ….

Precipitação útil (mm)

Tempo (h)

Precipitação útil (mm) Precipitação útil (mm) Precipitação útil (mm)

Tempo (h)Tempo (h)Tempo (h)

Caudal, Q

Tempo (h) Tempo (h) Tempo (h) Tempo (h)

Caudal, Q Caudal, Q Caudal, Q

Hietogramas com o mesmo volume útil Qual é a distribuição temporal que

conduz ao maior caudal de ponta?

Hidrogramas com o mesmo volume de cheia

What is the precipitation distribution patterns

that leads to the highest peak flow?

All hyetographs have the

same total ammount of

precipitation and this is the

same as the flood volume of

all hydrographs. Only the

time distribution changes.

Maximization of the flood peak

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 64 17-11-2015

nk

i

iproj

k

i

n

n

n

DaPPdtD

PPPdtaPdt

PPPdtaPdt

dtaPdt

11

121233123

112212

1

.........

33

22

n u Ordem u P Pu

0 0

1 u1 (5) P7 Pu7

2 u2 (2) P6 Pu6

3 u3 (1) P4 Pu4

4 u4 (3) P3 Pu3

5 u5 (4) P1 Pu1

6 u6 (6) P2 Pu2

7 u7 (7) P5 Pu5

8 0

0 1 2 3 4 5 6 7 8

u / umax

1

Precipitação útil (mm)

0 1 2 3 4 5 6 7 8

0 1 2 3 4 5 6 7 8

u / umax

1

Precipitação útil (mm)

0 1 2 3 4 5 6 7 8 The graphs are simetric around its

maximum value / Gráficos

simétricos em torno do seu máximo

Exercise

The unit hydrograph of a given watershed is indicated in the table. Assuming a

rainfall depth-duration-frequency curve for T=100 years equal to , with P in

mm and t in min, please compute:

• The hyetograph that maximizes the peak flow;

• The peak flow of resulting hyetograh;

• The peak flow that would result from a precipitation event with a uniform

precipitation rate. O hidrograma unitário de determinada bacia hidrográfica encontra-se representado no seguinte quadro.

Desprezando as perdas da precipitação e sabendo que a linha de possibilidade udométrica para o período

de retorno de 100 a na região é com P em mm e t em min, determine:

– a distribuição temporal da precipitação que maximiza o caudal de ponta de cheia para esse período de

retorno,

– o referido caudal máximo de ponta de cheia,

– o caudal de ponta de cheia que resultaria de uma precipitação com distribuição temporal uniforme.

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 65

5.05 tP

t (h) 0.0 0.5 1.0 1.5 2.0 2.5 3.0

u (m3/s/mm) 0 10 30 25 12 6 0

17-11-2015

5.05 tP

Transformation of the unit

hydrograph

Unit hydrograph transformation

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 67 17-11-2015

One unit of net precipitation

during dt produces the UH for dt. Precipitação unitária com uma duração

de dt e hidrograma unitário para uma

duração de dt.

One can compute the flood

hydrograph produces by a rainfall

event discretized in dt. O hidrograma resultante de um

hietograma com um intervalo de

cálculo dt pode ser calculado a partir

de umhidrograma unitário para uma

duração de dt.

What should we do when the

precipitation is discretized in a

time interval distinct from dt? O que fazer quando o intervalode de

cálculo é diferente de dt? ?

0 1 2 3 4 5

u

0 1 2 3 4 5

Q

6 7 8

Estimation of unit hydrograph for a dt2 distinct from dt1

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 68 17-11-2015

Curva S

Curva S

UHs for dt1 Hidrogramas unitários para uma

precipitação unitária de duração

dt1

UHs for dt2 Hidrogramas unitários para uma

precipitação unitária de duração

dt2

Hydrograph from a continuous

long with an intensity of 1/dt1 Hidrograma resultante de uma

precipitação constante com

intensidade 1/dt1

Hydrograph from a continuous

long with an intensity of 1/dt2 Hidrograma resultante de uma

precipitação constante com

intensidade 1/dt2

(1) (2)

(3)

HU for dt1

Sum of

various HU

S curve for a precipitation

intensity of 1/dt1

S curve movement (translation)

by dt2 and subtraction of the

two S curves

HU for dt2

Multiplication by dt1/dt2

S curve for a precipitation

intensity of 1/dt2

S-curve shift and HU computation

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 69 17-11-2015

Ordinates of the UH for dt2

dt2

S’ curve for i=1/dt2

S’ curve for i=1/dt2 translated by dt2

Tempo Curva S Curva S' Tempo Curva S Curva S HU dt2

i=1/dt1 i=1/dt2 i=1/dt2 desfas. dt2

0.000 0 0.00 0.00 0.0 0.00 0

0.143 1 0 0.58 0.42 0.2 0.75 0.00 0.75

0.286 1 1 0 1.75 1.25 0.4 2.25 0.75 1.50

0.429 2 1 1 0 3.50 2.50 0.6 3.65 2.25 1.40

0.571 1 2 1 1 0 4.90 3.50 0.8 4.55 3.65 0.90

0.714 1 1 2 1 1 0 5.95 4.25 1.0 5.00 4.55 0.45

0.857 1 1 1 2 1 1 0 6.65 4.75 1.2 5.00 5.00 0.00

1.000 0 1 1 1 2 1 1 0 7.00 5.00 1.4 5.00 5.00 0.00

1.143 0 0 1 1 1 2 1 1 0 7.00 5.00 1.6 5.00 5.00 0.00

1.286 0 0 1 1 1 2 1 1 0 7.00 5.00 1.8 5.00 5.00 0.00

1.429 0 0 1 1 1 2 1 1 0 7.00 5.00 2.0 5.00 5.00 0.00

1.571 0 0 1 1 1 2 1 1 0 7.00 5.00 2.2 5.00 5.00 0.00

1.714 0 0 1 1 1 2 1 1 0 7.00 5.00 2.4 5.00 5.00 0.00

1.857 0 0 1 1 1 2 1 1 0 7.00 5.00 2.6 5.00 5.00 0.00

2.000 0 0 1 1 1 2 1 1 0 7.00 5.00 2.8 5.00 5.00 0.00

2.143 0 0 1 1 1 2 1 1 0 7.00 5.00 3.0 5.00 5.00 0.00

2.286 0 0 1 1 1 2 1 1 0 7.00 5.00 3.2 5.00 5.00 0.00

2.429 0 0 1 1 1 2 1 1 0 7.00 5.00 3.4 5.00 5.00 0.00

2.571 0 0 1 1 1 2 1 1 0 7.00 5.00 3.6 5.00 5.00 0.00

2.714 0 0 1 1 1 2 1 1 0 7.00 5.00

2.857 0 0 1 1 1 2 1 1 0 7.00 5.00

3.000 0 0 1 1 1 2 1 1 0 7.00 5.00

3.143 0 0 1 1 1 2 1 1 0 7.00 5.00

3.286 0 0 1 1 1 2 1 1 0 7.00 5.00

3.429 0 0 1 1 1 2 1 1 0 7.00 5.00

3.571 0 0 1 1 1 2 1 1 7.00 5.00

Hidrogramas unitários para dt1 desfasado de dt1

Estimation of unit hydrograph for a dt2 distinct from dt1

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 70 17-11-2015

Change of

discretization interval

Multiplication by

dt1/dt2

Translation by

dt2

HU for dt1

Sum

Exercise

Consider the S curve of a given watershed represented in the table. Determine:

– Time of concentration of the watershed

– Area of the watershed

– Unit hydrograph for a duration of 0,5h

O hidrograma em S de determinada bacia hidrográfica encontra-se representado no

seguinte quadro. Com base nesse hidrograma determine:

– o tempo de concentração da bacia hidrográfica;

– a área da bacia hidrográfica;

– o respectivo hidrograma unitário para a duração de 0,5 h.

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 71

t (h) 0,0 0,5 1,0 1,5 2,0 2,5

S (m3/s/mm) 0 2 10 20 36 36

17-11-2015

Exercise

The following direct flow hydrograph was generated from a long,

continuous, uniform precipitation event with a net rate of 600 mm/h.

Determine the unit hydrograph for 0.3 h.

Em determinada bacia hidrográfica, em resultado de uma precipitação útil com grande

duração e intensidade constante de 60 mm/h, obteve-se o hidrograma do escoamento

directo indicado no quadro. Determine o hidrograma unitário para a duração de 0.3 h.

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 72

t (h) 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 …

Qd (m3/s) 0 60 150 280 320 340 350 350 …

17-11-2015

Exercise

The following table shows the unit hydrograph of a given watershed for a

0,5h duration. Determine the unit hydrograph for 20 min.

Apresenta-se no quadro seguinte o hidrograma unitário de determinada bacia hidrográfica

para a precipitação útil com a duração de 0.5 h. Calcule o HU para uma duração de 20 min

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 73

t (h) 0.0 0.5 1.0 1.5 2.0 2.5

u (m3/s/mm) 0 15 34 17 9 0

17-11-2015

Flood attenuation in reservoirs

Reservoir storage zones

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015

Flood storage volume / pool

Volume de encaixe de cheias

Net/useful storage

Volume útil

Dead storage / Volume morto

NPA

NMC

Nme

Discharge Descarga

Turbined flow Volume turbinado

H

Evaporation Evaporação

Inflow Afluências

Uptake/abstraction Captação

Energy Energia

75

NMC –Maximum design storage level / Nível de maxima cheia

NPA – Full storage level or top of conservation pool / Nível de pleno armazenamento

Nme – Minimum operation level / Nível minimo de exploração

17-11-2015

Sizing of the flood control storage zone

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 76

17-11-2015

Encaixe de cheias

Volume útil

Volume morto

NPA

NMC

Nme

Descarga

Tempo Tempo

Qafluente

Qefluente

Volume “encaixado”

Redução do pico da cheia

Inflow

Outflow

Peak reduction

Controled flood volume

Net storage pool

Dead storage pool

Flood storage pool

In a reservoir the outflow is a

function of the store volume and of

the outflow control devices.

For example:

Inflow and outflow discharge

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 77

Inflow from the watershed, obtained from the

flood analysis.

23

_ 2 icali HgbcQe

17-11-2015

i Tempo(h) Qai Vi Hi Qei atrib Qei calc Abs(Qei_atrib-Qei_calc)

0 0 0 0 0 0 0 0

1 dt Qai 1 x x x x x

2 2dt Qai 2 x x x x x

3 3dt Qai 3 x x x x x

4 4dt Qai 4 x x x x x

5 5dt Qai 5 x x x x x

… … … … … … … …

Outflow discharge computation

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 78 17-11-2015

alb

ii

A

VH

dtQeQeQaQa

VV iiiiii

22

111

23

_ 2 icali HgbcQe

Valores

inicialmente

arbitrários

Goal seek: Abs(..)=0

bHgbcQaH 23

max 23

Outflow discharge computation

• For each time step:

• We need to automate this computation !

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 79 17-11-2015

alb

ii

A

VH 1

1

dtQeQeQaQa

VV iiiiii

22

111

23

12ˆ1

iHgbceQi

1iQearbitrar

??01,0ˆ11

ieQQei

1

ˆ1

ieQQei

Stop S

N

Goal seek global via VB

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 80 17-11-2015

Col Qei_atrib Col Abs(…)

Goal seek aplica-se de t=1 a ….

Mathematical modelling

Existing mathematical models

HEC – Hydrological Engineering Center (USACE).

• Hydrologic model:

– Input: Hietogram;

– Output: Hidrogram;

– e.g.: HEC-HMS (ex HEC1);

• Hydraulic model:

– Input: Hidrogram;

– Output: h, U, flooded areas;

– e.g.: HEC-RAS (ex HEC2);

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 17-11-2015

Modelação

hidrológica

Modelação

hidráulica

Análise de registos

históricos

82

Hydrologic model

IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 83 17-11-2015

Hydraulic model

17-11-2015 IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015 84

Hydraulic model - results

17-11-2015 IST: Hydrology, environment and water resources 2015/16 © Rodrigo Proença de Oliveira, 2015

1748.12*1699.07* 1650.01*

1600.96*

1404.74*

1355.69*

1306.63*

1257.58*

1208.53

1179.97

1134.45

1086.27*

1038.10*

989.934*

941.763*

893.591*

845.419*

797.247*

749.076*

700.904*

652.732*

604.560*

556.389*

508.217*

460.045*

411.873*

363.702*

Novas seccoes_ApresntacaoNov2003 Plan: Plan 06 13/11/2003 4:52:18 PMGeom: novasseccoes_testecoordinates Flow: steady1

Legend

WS PF 1

WS PF 2

WS PF 3

Ground

Bank Sta

Ground

1846.23*

1797.17*

1748.12*

1699.07*1650.01*

1600.96*

1551.90*

1502.85*

1453.8*

1404.74*

1355.69*

1306.63*

1257.58*

1208.53

1179.97

1134.45

1086.27*

Novas seccoes_ApresntacaoNov2003 Plan: Plan 06 13/11/2003 4:52:18 PMGeom: novasseccoes_testecoordinates Flow: steady1

Legend

WS PF 1

WS PF 2

WS PF 3

Ground

Bank Sta

Ground

4115.34

4078.38

4024.89

4009.73

4000.74

Novas seccoes Plan: Plan 06 10/10/2003 3:17:13 PMGeom: novasseccoes_testecoordinates Flow: steady1

Legend

WS Max WS

Ground

Bank Sta

85


Recommended