a) More data / longer record - Home - Reduce FloodingPresentation by W. R. Dupre’ (UH) 2018...

9/9/2018

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Houston Geological Society Presents

Flooding and Floodplains in the Houston Area:Past, Present, and Future: Part 2

An Informational Workshop

Presented August 24, 2018@ Kingwood, TX

Dr. William R. Dupre’Professor Emeritus

Earth & Atmospheric SciencesUniversity of [email protected]

6) The “100-year” rain/flood/floodplain can change w/time!

……but why?

a) More data / longer recordb) Changing land usec) Structural changesd) Changing climate

Presentation by W. R. Dupre’ (UH) 2018

1940-1975

U.S. GEOLOGICAL SURVEYFact Sheet 229-96 Presentation by W. R. Dupre’ (UH) 2018

55 years of record

a) More data / longer record

25 years of record 1977

1961

1964Presentation by W. R. Dupre’ (UH) 2018

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Texas


Duration

Precipita

tion (in

ches)

2 yr

5 yr

10 yr

25 yr

50 yr

100 yr

Precipita

tion (in

ches)

1% flood(“present”)

4 day

24 hr

6 hr

2 hr

?

Depth-Duration-Frequency (DDF) Curves


Duration

Precipita

tion (in

ches)

Precipita

tion (in

ches)

1% flood *(after Atlas 14)

1% flood(“present”)

4 day

24 hr

6 hr

2 hr

?


> 5” inc.

Depth-Duration-Frequency (DDF) Curves

*https://riparianhouston.com/2017/11/24/harris‐county‐close‐up‐of‐preliminary‐atlas‐14‐data/

b) Changing Land Use- Urbanization

Increased impervious surfaces:- decreased infiltration (increases runoff)- faster runoff (decreases lag time)

Bridges – (impediments to flow)Storm drains (decrease lag time)Failure of storm drains

- Deforestation/agricultural changesPresentation by W. R. Dupre’ (UH) 2018

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Urbanization of Drainage BasinU.S. GEOLOGICAL SURVEY

Fact Sheet 229-96 Presentation by W. R. Dupre’ (UH) 2018

17 years*

21 years

* Note longer record isn’t always better!

Time (minutes)

Intensity

(mm/hou

r)

Infiltration capacity

Rainfall Intensity

Rainfall Excess

= Runoff


highInfiltration is ....

lowRunoff is .....

Surface Slope low steepSoil Type sandy clay‐richPpt. Intensity gentle heavySoil Saturation low high Vegetation hi % low %Land Use natural urbanized

low

highPresentation by W.R. Dupre’, Univ. of Houston, 2018

After Urbanization

Before

After


1) Decreased Lag Time2) Increased Peak Stage/Discharge1) Decreased Lag Time2) Increased Peak Stage/Discharge3) Increased Volume of Runoff

Time

Stage or Disc

harge

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1949

1960Hydrographs from Similar Sized Stormson Brays Bayou

U.S. GEOLOGICAL SURVEY Presentation by W. R. Dupre’ (UH) 2018

Harvey


Peak Floods – Brays Bayou 08075000

1946

1958

Harvey

By the 1980s, > 95 % of the Brays Bayou watershed was developed.

Greater Houston Strategies for Flood Mitigation, 2018

Allison

1978

Meyerland


Peak Floods – Brays Bayou 08075000

1958

1935

1929

1929

HarveyHarvey1935 ?

Post Addicks Dam

Annual Daily Peak Discharge (cfs)

Brays Bayou@ Rice Ave

Buffalo Bayou@ Shepard


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https://waterdata.usgs.gov/nwis/uv?site_no=08068000

Post Lake Conroe

10/19948/2017

11/1940

5/201611/1998

4/1926

1913


Annu

al Pea

k Discha

rge (cfs)

West Fork San Jacinto River near Conroe

1000 ft

https://www.harriscountyfws.org/ Presentation by W. R. Dupre’ (UH) 2018

Roads & Bridges can act like Dams!

http://sspeed.rice.edu/sspeed/downloads/2018_Conference/presentations/D2‐13.%20Brand.pdf

Add

Addicks

Barker

Impervious surface in Harris County increased by 25 % 1996 to 2011

Land developed 2001‐2010

Remaining Coastal Prairie 2010

https://projects.propublica.org/houston‐cypress/ Presentation by W. R. Dupre’ (UH) 2018

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Remnant Prairie in Study Area

Texas Water Development Board Contract Report Number 1248321466 Presentation by W. R. Dupre’ (UH) 2018

Drainage DivideRoots to 15’

Atticks Watershed

UpperCypress Creek Watershed

Texas Water Development Board Contract Report Number 1248321466

Coastal P

rairie

Agric

ulture

Develope

d

Increased runoff with loss of coastal prairie D

irect ru

noff (inche

s)

6.4” (Residential)

2.6”


Restoration of 1 acre of prairie would:

‐ increase the infiltration capacity of undeveloped land by~3.5 inches in a 100‐year flood event…

‐ offset the volume impact of ~ 2 acres of a single‐family subdivision, or ~ 1 acre of commercial or retail development.

Texas Water Development Board Contract Report Number 1248321466

Decreased Runoff due to Prairie Restoration


c) Structural Changes

1) Dams

2) Levees

3) Channelization

4) Detention/Retention Basins


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Dam built in 1961U.S. GEOLOGICAL SURVEYFact Sheet 229-96 Presentation by W. R. Dupre’ (UH) 2018

32 years24 years

* Note longer record isn’t always better!

1) Effect of Dams on Flooding12/31/1977

10/28/2017 Effects of Building a Dam:Inceased deposition

(and flooding) upstream

Decrease flooding & increased erosion

downstream

Why???Other implications??

Press & Siever, 2004 Presentation by W. R. Dupre’ (UH) 2018

Kingwood! ??

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River Profile Before Dam

BaseLevel

River Profile After Dam

OldBaseLevel

New Base Level

Backwater curve

Increasedflooding

Increased backwater due to deposition of sediment

Kissling et al., 2018

Delta progradation into Lake Constance, Austria

Deposition of River Mouth Bar

Increased backwater due to deposition of sediment

Kissling et al., 2018

Delta progradation into Lake Constance, Austria

Deposition of River Mouth Bar

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TWDB (2013)Volumetric and Sedimentation Survey of LAKE HOUSTON December 2011 Survey

1954 1960 1970 1980 1990 2000 2010

150,000

100,000

125,000

Total R

eservoir Ca

pacity (a

cre‐feet)

50,000

158,553 acre‐feet146,769 acre‐feet

136,381 acre‐feet124,661 acre‐feet

~ 21% filled in 57 years


Growth of subaerial delta

Deposition of lake‐bottom sediments

Half‐life ~135 years

@ US‐59

@ H‐99

@ I‐45

KingwoodLake

Houston

LakeConroe1/1/1973

1/1/1954


Cypress Creek near Westfield

W. Fork San Jacinto near Conroe

Spring C.

Cypress C.

Suspended Sediment Rating Curve* Cypress Creek near Westfield, TX USGS 08069000

Brown & Root Services (2000) Regional Flood Protection Study Lake Houston Watershed Flood Program (Final Report) Presentation by W. R. Dupre’ (UH) 2018

* Establishes a relationship between measured suspended sediment discharge with measured water discharge to allow

extrapolation to periods when only water discharge is measured.

Suspended Sediment Rating Curve West Fork San Jacinto River near Conroe, TX USGS 08068000

Brown & Root Services (2000) Regional Flood Protection Study Lake Houston Watershed Flood Program (Final Report)

West Fork San Jacinto River near Conroe, TX (post Lake Conroe)

Cypress Creek near Westfield, TX

~10x increase


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Basin Range % Total

Cypress Creek 70,000-160,000 52-58%Spring Creek 30 000-65,000 22-24%W. Fork SJ 35,000-50,000 26-18%

Total 135,000-275,000 100%

West ForkSan Jacinto

East ForkSan Jacinto

Spring

1204101

Buffalo – San Jacinto

1204102

KingwoodSpring Creek

Cypress Creek

Anticipated Sediment Loads (tons/year)

“…the major source of the total sediment load, [into Lake Houston] …is contributed

by Cypress Creek….” [BUT]

Presentation by W. R. Dupre’ (UH) 2018Brown & Root Services (2000)

West ForkSan Jacinto

East ForkSan Jacinto

Spring

1204101

Buffalo – San Jacinto

1204102Kingwood

Spring Creek

Cypress Creek


Caveats:These data are the only ones presently available for measuring the relative sediment load of major tributaries. However, they do not:

1) …measure sediment during high flood flows when most sediment is transported.

2) …reflect any impact of post‐1999 changes in land use.

3) …measure transport of bedload sedimentTherefore, more data are needed before an accurate estimation of the sediment

budget can be made!Brown & Root Services (2000)

Collins et al., Formulating Guidelines for Reservoir Stability. Presentation by W. R. Dupre’ (UH) 2018 Presentation by W. R. Dupre’ (UH) 2018

Lane’s Balance between Sediment & Energy

Lane, 1955, The Importance of Fluvial Morphology in Hydraulic Engineering

ADD

REMOVE

INCREASE

LOWER

Sediment(size & supply)

Energy(slope & discharge)

EROSION

EROSION

DEP

OSITION

DEP

OSITION

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Suspended Sediment Rating Curve West Fork San Jacinto River near Conroe, TX USGS 08068000

West Fork San Jacinto River near Conroe, TX (pre Lake Conroe)


West Fork San Jacinto River near Conroe, TX (post Lake Conroe)

Average sediment load (pre‐dam)59,722 tons/yr

Average sediment load (post‐dam)44,738 tons/yr~25 % decrease

Suspen

ded Sedimen

t Disc

harge (ton

s/da

y)

River Discharge (cfs)Brown & Root Services (2000) Regional Flood Protection Study Lake Houston Watershed Flood Program (Final Report)

•River Bar deposition

•Overbank deposition

•Delta Bar deposition

•Obstructions to flow

• Sand Pits

Sites of Sedimentation


Sources of Sediment

•River Erosion

•Urbanization

• Sand Mining

Causes of Changes in Sediment & Sedimentation

•Building Dams•Increased Runoff

•due to urbanization•due to climate change [“non‐stationary climate”]

•Sand Mining•Construction•Constrictions (local sites of deposition)


Deposition

Erosion

Erosion

Deposition


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1‐22‐1995500 feet


12‐22‐1995 500 feet1‐23‐2017

1995

10/2017

300 ft


1995

500 feet

NET EROSION

NET DEPOSITION

River Bank Changes: 1995‐2017

300 ft(~13.5 ft/yr)

350 ft(~16 ft/yr)


500 feet

1) It can damage or destroy homes well above and outside the regulatory floodplain.

2) It can destroy both structures and property, making rebuilding impossible.

3) It can occur progressively during floods smaller than the 1% flood, resulting in cumulative, long‐term losses.

ASFPM Arid Regions Committee Riverine Erosion Hazards White Paper December 22, 2010

Riverine erosion may be even more problematic than flood inundation because:


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Required FEMA evaluate the technological feasibility of

mapping Erosion Hazard Areas (both coastal and riverine) and the economic impact on the National Flood Insurance

Program.

National Flood Insurance Reform Act (NFIRA) of

1994:

FEMA: Riverine Erosion Hazard Areas (1999) Presentation by W. R. Dupre’ (UH) 2018

Effect of Changing Land Use on Sediment Production

Wolman, 1967 Presentation by W. R. Dupre’ (UH) 2018

Morris & Fan, 2010, Reservoir Sedimentation Handbook (after Livesey, 1975)

Schematic Sequence of Changes in Sediment Yield:Rural Watershed to Urbanized Basin


Time (years)

Annu

al Sed

imen

t Yield

3/10/2011100 ft.


4/22/2012

100 ft.

Sediment entering West Fork from urbanization in the tributary.

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https://communityimpact.com/houston/development‐construction/2015/08/26/development‐strains‐san‐jacinto‐river‐ecosystem/

Riparian BufferRiver Sand Pit

Types of River Sand Mining Pits:

Sandercock & Ladson, 2014, Review of floodplain mining impacts and risks

In‐stream pitFloodplain wet pit

Terrace pit


Terrace pit

In‐StreamMining


1‐14‐2006

500 ft

Brazos River

3‐31‐2006“- Channel modifications such as widening or deepening the

channel, creation of deep pools, loss of riffles, alteration of bedload, alteration of channel flow, and degraded aesthetics.

- Upstream and downstream erosion and related impacts.- Modifications of aquatic habitat including spawning beds, nursery habitat, shellfish habitat, and riparian habitat.

- Degradation of water quality including increased turbidity, reduced light penetration, increased temperature, and resuspension of organic or toxic materials.

- Bridge scour and other impacts to infrastructure”

Possible In-stream Sand Mining Impacts


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Floodplain Mining‐“The main hazard is pit capture, via: lateral migration of river channel into the pit, sub‐surface piping into pits and subsequent failure of pit walls, or spill of water into and through the pit.”

‐“Pit capture impacts on a rivers geomorphic characteristics, sediment transport, hydraulics, hydrology, water quality and aquatic habitat, with these impacts extending upstream and downstream of the pit as well as the area of the pit itself.”

Jacobs & Moroka, 2014, Review of floodplain mining impacts and risks

‐“After pit capture the stream will deposit its bedload in the pit,” which may result in both upstream and downstream erosion.”


Guidelines for Maricopa County, Arizona

Presentation by W. R. Dupre’ (UH) 2018Jacobs & Moroka, 2014, Review of floodplain mining impacts and risks

Avoid siting pits in a ‘channel migration zone’“In Washington State and Arizona , floodplain mine regulators have adopted the concept of a Channel Migration Zone to assist in the identification of suitable sites (Rapp & Abbe, 2003).

This considers the dynamism of the river channel through historical analysis of channel migration to identify areas that are disconnected from river migration.

Mining is restricted to floodplain terraces or areas of the floodplain where there are structural measures in place to limit the migration of the channel.”

Presentation by W. R. Dupre’ (UH) 2018Jacobs & Moroka, 2014, Review of floodplain mining impacts and risks

Erosion Hazard Area

“An area where, based on erosion rate information and other historical data, [lateral] erosion or avulsionis likely to result in damage or loss of buildings or infra‐structure within a 60 year period*. “

(Section 577 of National Flood Insurance Reform Act of 1994)

FEMA: Riverine Erosion Hazard Areas (1999)

* Time period may vary with statute


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100 feet


12‐31‐2001 1‐25‐2004

Narrow (<25’), non‐vegetated buffer: HIGH erosion (and pit capture) hazard.

7‐31‐2015

100 ft.

BSpit formed by sediment entering the pit

Q ~55 cfs


April 2015flood breach

1‐23‐2017

100 ft.

B


Post 4/2016fill

New spit formed by sediment entering the pit during Tax Day Flood

April 2015flood breach

Post 8/2015fill


Mosaic artifact

1000 ft

500 m

Mosaic artifa

ct


Turbidity plumes indicating water and sediment flow into the sand pits during Hurricane Harvey on August 30, 2017

Edge‐enhanced Google Image

Color‐enhanced Google Image

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2) Effect of Levees

Before

After

But !1- Encourages development on prior floodplain

2- Levees can fail, either by: - overtopping, - poor maintenance, - erosion, - subsidence, or - under-seeping!

3- Levees can act as dams, trapping water & flooding homes


3) Early Channelization Approaches

•Increase channel cross section area to hold more water (widening & deepening);

•Increase flow velocity, e.g.•Concrete lining channel• Straightening channel• Improving cross sectional efficiency

Presentation by W.R. Dupre’, Univ. of Houston, 2018

y y ,Brays Bayou, 1916

Beechnut

Stella Link

Renw

ick

Brays Bayou, 1976Brays Bayou, 1976

Presentation by W.R. Dupre’, Univ. of Houston, 2018

1 foot contour interval

Beechnut

Chim

ney Ro

ck

Stella Link

Renw

ick

1916 Base Map1 foot contour interval


Slope increased by 2xVelocity increased by ~ 1.4x!

1976 Bayou

1916 Bayou

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But isn’t Reduced Flooding Good?

• Concrete-lining & removal of natural vegetation reduces natural habitats.

• Concrete-lined channels look bad and reduce groundwater recharge and baseflow.

• Channelization can increases downstream flooding and erosion!

• Encourages development of floodplainsPresentation by W. R. Dupre’ (UH) 2018

4) Effects of Detention Basins•On‐site: detains storm water on site before it enters the channel

• In‐line [linear]: Deep areas adjacent to the channel that can store floodwater once it begins rising in the channel.

•Regional: built by flood control agencies to address flooding on a larger geographic scale and is funded by taxes or stormwater fees paid by a number of developers. Regional detention is used to reduce existing flooding or help prevent increased flooding from new developments. (may be wet‐bottom or dry‐bottom)

Modified from GHFMC, Strategies for Flood Mitigation, 2018 Presentation by W. R. Dupre’ (UH) 2018

Detention Basin

GHFMC Fact Sheet 3

Pre‐development

Post‐development

With detention


d) Changing Climate

“There has been a growing concern among users of NOAA Atlas 14 products that they …… may not

be appropriate in presence of non-stationary climate.”

ANALYSIS OF IMPACTS OF NON‐STATIONARY CLIMATE ON PRECIPITATION FREQUENCY ESTIMATES

www.nws.noaa.gov/oh/hdsc/current‐projects/progress/201804_HDSC_PR.pdf Presentation by W. R. Dupre’ (UH) 2018

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ANALYSIS OF IMPACTS OF NON-STATIONARY CLIMATE ON PRECIPITATION FREQUENCY ESTIMATES

- The current NOAA Atlas 14 frequency analysis methods are based on the assumption of stationary climate in both historic and future precipitation records.

- As such, they may not be suitable for frequency analysis in the presence of non-stationary climate conditions…

- It has thus become necessary to assess the potential for incorporating non-stationarity in precipitation frequency estimates.

www.nws.noaa.gov/oh/hdsc/current‐projects/progress/201804_HDSC_PR.pdf Presentation by W. R. Dupre’ (UH) 2018

NOAA Atlas 14 and Climate Change•2018 version will assume “stationarity”•Reasons for change from 1961

•Better methods•More stations• Longer data records• Intensifying rainfall

•But: 2018 version will already be “out of date”•Current risk higher, future risk higher still

Texas State Climatologist, John Nielsen‐Gammon, Texas A&M University Presentation by W. R. Dupre’ (UH) 2018

Key Messages1) Harvey was exceptional2) Odds of extreme rainfall have increased and

will continue to increase• Increase in probability (ballpark) by a factor of 3 (2x‐8x) / °C global warming

• Increase in rainfall (ballpark) ~15% (10‐30%) per °C global warming

75Texas State Climatologist, John Nielsen‐Gammon, Texas A&M University

http://climatexas.tamu.edu

Presentation by W. R. Dupre’ (UH) 2018 Presentation by W. R. Dupre’ (UH) 2018van Oldenborgh et al., (2017) Environmental Research Letters

…we conclude that global warming made the precipitation [from Harvey] about 15% (8%–19%) more intense, or equivalently made such an event three (1.5–5) times more likely.

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https://nca2014.globalchange.gov/highlights/report‐findings/extreme‐weather#intro‐section‐2

One measure of heavy precipitation events is a two-day precipitation total that is exceeded on average only once

in a 5-year period.

U.S. Trend in Heavy Precipitation

Relativ

e Num

ber o

f Extreme Even

ts (%

)


Hydrological

Geophysical

Total

Nat

ural

Dis

aste

rs A

nnua

lly

www.munichre.com/topics‐online/en/2018/01/2017‐year‐in‐figures Presentation by W. R. Dupre’ (UH) 2018

Number of Global Natural Disasters: 1980-2017

Structural Responses: (1930’s‐present): e.g.building dams, levees, floodwalls, channelization‐Flood Control Act of 1936.

Floodplain Management: (1960’s‐present):Combined floodplain management with structures‐National Flood Insurance Program of 1968;‐National Disaster Protection Act of 1973;‐Biggert‐Waters Flood Insurance Reform Act 2012.

Post‐flood Non‐structural Mitigation: (1980’s‐present):Includes property acquisition and land use.

Changing Approaches to Flood Control

Presentation by W. R. Dupre’ (UH) 2018 www.uh.edu/class/hobby/harvey/ Presentation by W. R. Dupre’ (UH) 2018

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www.uh.edu/class/hobby/harvey/ Presentation by W. R. Dupre’ (UH) 2018

Increase in property tax? Increase in sales taxes?

www.uh.edu/class/hobby/harvey/ Presentation by W. R. Dupre’ (UH) 2018

No increase

No increase

The 237 Flood Bond Projects Include:$1.2 billion (~50%) for channel improvements $401 million (~15%) for detention basins

$242 million (~10%) for floodplain land acquisition$12.5 million (~5%) for new floodplain mapping$1.25 million for an improved early flood warning system

$500 million (20%) unallocatedHouston Chronicle: Tuesday, August 7, 2018 Presentation by W. R. Dupre’ (UH) 2018

Structural

Non

‐structural

a) More data / longer record - Home - Reduce FloodingPresentation by W. R. Dupre’ (UH) 2018...

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