data access and engineering modeling - kamm · hydraulic modeling guidance cross sections must be...

Data Access and Engineering

Modeling

KAMM Regional Training

Overview

Study Area Identification

Study Method Factors

Floodplain Mapping Process Overview

Available Methodology and Analysis

General Requirements, Guidelines and

Standards

Important Terms

Method Examples and Selection Process

Data Sources

http://www.kymitigation.org/http://www.kymitigation.org/

Study Area Identification and



Identifying Study Areas

CNMS status is Unverified

New Data

Topographic -LiDAR

Hydrologic – Gages, regression equations,

design storm changes

Unmapped areas affected by flooding

1 square mile of drainage area

Physical changes

Recent or planned development

Stream changes – fill, migration, deposition,

channelization, dredging

Structure changes – culverts added or

removed, road construction, flood control

structure changes

Modeling Errors

Software upgrades (i.e. HEC-1 to HEC-HMS)



Budget

Population Affected

Risk

Community Request


Study Method Factors Cont.

Previous Effective

Zone/Mapping, up and

downstream models

Nature of Overbank and

Channel Flow (1-D versus 2-D)

Flow analysis – depth and/or

velocity vary with time

Data available

Hydraulic structures

In general, the simplest model that can

solve the problem with accuracy should be

the one selected.


Floodplain Mapping Process

Overview


Floodplain Mapping Overview

Data Required

Topographic Data

Flow Data – multiple

recurrence intervals

Channel delineation

and flow direction

Cross Section Data


Topographic Data


Flow Data


Channel and Cross Sections


Model Results


Floodplain Results


Available Methodology and Analysis


Available Riverine Hydrology Study Methods

Compute hydrograph from

spatial and temporal rainfall

data, calibration

Sub-basins connected through

system of stream reaches

Statistical analysis of stream

gage data

Analysis based on regional

regression equations for rural

or urban watersheds

Increasing Level of Detail


Riverine Hydraulic Study Analysis

Steady State Zone AE Zone AE

(without floodway)

Zone A

Analysis

Zone A

Analysis

BLE

Unsteady State

(1-D)

Zone AE

1D Unsteady

Analysis

Combined 1D/2D

Unsteady Analysis

Unsteady State

(2-D)

Zone AE

2D Unsteady

Analysis

Zone A

Analysis 2D

BLE

Increasing Level of Detail

Hydraulic Method

More detailed is not always the best choice.


General Requirements, Guidelines

and Standards


Topographic Data Requirements and Considerations

Updated topographic data is required to update flood data.

Consider the following:

Contour interval — should be 4 feet or better (2 feet in flat terrain).

Currency of data—whether significant changes (e.g., hydraulic

structures, significant channel modification, development near

channel) have occurred since the data was acquired. If significant

changes not included, supplement with field survey.

SID #44 requires all elevation data to be processed to the bare earth

terrain in the vicinity of floodplains that will require hydraulic

modeling.

Additionally, SID #50 requires that digital terrain model input for a two-

dimensional model must cover the entire 2-D study area and the

derivation or development of the grid must be clearly documented.

See Elevation Guidance


Floodplain Mapping with LiDAR

• High resolution topographic data creates more accurate

floodplains


Hydraulic Modeling Guidance

Cross sections must be placed perpendicular to flood flow and

extend beyond the most extreme event modeled.

Cross sections must be spaced so that the geometry and hydraulic

roughness of the reach between adjacent cross sections varies

gradually and that variation can be estimated as linear.

Not required but generally spaced 1,000 feet or less for AE

analysis.

Cross Section Guidance being prepared will include cross section

and structure survey guidance.

See General Hydraulics Considerations Guidance Document and

Hydraulics 1D or 2D guidance.


General Hydraulic Standards

SID # 54 - Where flood elevations are produced

from a hydraulic model, they can be published

as BFEs unless the responsible engineer

documents why they should not be issued.

SID # 74 - The hydrologic, hydraulic, and coastal

analyses and the final regulatory products must

be certified by a registered professional

engineer.


Riverine Model Requirements SID #90 - The methods and models used to evaluate the flood

hazard must be technically reliable, must be appropriate for

flood conditions and produce reasonable results.

Software list available on fema.gov includes: HEC-RAS

3.1.1 and up, HEC-2 4.6.2.1, XP-SWMM 8.52 and up, ICPR

2.20, FLO-2D 2007.06/2009.06, etc.


Riverine Study Requirements

SID # 84 requires all riverine engineering Flood Risk Projects

consist of a hydraulic model with multiple frequencies:

(0.2%, 1%, 2%, 4%, 10%, and 1% plus annual-chance

exceedance events).


Important Terms


1% +

1% Plus

For flooding sources where discharges

were estimated using regression

equations, the 1% annual chance

discharge has an associated average

predictive error percentage. This

error is then added to the 1% annual

chance discharge to calculate the 1%

plus discharge.

For flooding sources with gage- or

rainfall-runoff-based discharge

estimates, the upper 84-percent

confidence limit of the discharges is

used to compute the 1% plus flood

elevations.


1% -1% Minus

This error is then subtracted

from the 1% annual chance

discharge to calculate the 1%

minus discharge.

These calculations help provide a

confidence range within which

the actual 1% annual-chance

discharge at a location is likely

to fall.

If falls within the 68-percent

confidence interval of the gaged

data, then considered

reasonable.

Often used with automated

engineering for CNMS checks.


Future-Conditions 1%Future-Conditions Communities experiencing urban growth may use

future conditions hydrology and hydraulics.

For example increase in impervious area, structures

modifications, future land-use determinations

Some communities regulate based on future

conditions.

When requested by community officials, FEMA allows

inclusion of future conditions on FIRMs and FIS

usually shown as shaded Zone X.

Pros: Eliminates two sets of maps for communities

who enforce future condition regulations, increases

ownership of FIRMs, provides CRS credit, reduction

in future losses, and better partnership with FEMA.

Cons: projected conditions, increase in appeals, and

greater expense.

Not used for flood insurance purposes.


Steady vs. Unsteady Flow

Steady Unsteady

Gradually varying flow Flow attenuation

No flow attenuation Reversed flow during flooding

Rapidly varied flow

Depth of flow/velocity vary with time

Inflow entered as hydrographs


1-D vs 2-D

Majority of studies are steady-state flow, 1-D hydraulic

models

Increasing number of unsteady flow, 1-D and 2-D

hydraulic models being prepared

1-D 2-D

Confined flow Unconfined, split/diverted flows

Flow generally in one direction Flow moving in multiple directions

Wide and flat floodplains

Shallow flooding

High resolution topographic data

required


Floodway

A regulatory floodway is used to regulate development

to ensure there are no increases in upstream flood

elevations.

The community is responsible for maintaining the

floodway

RIVER

SURCHARGE = 1 FT

1% CHANCE FLOODPLAIN

FLOODWAY


Method Examples and Selection

Process


Example Mapping Method:

Zone AE Redelineation

Low population growth and development potential

Flood risk not significantly changed

Valid effective model

Updated topographic data available

Limited budget

No appeal period since elevations unchanged


Example Method of Analysis:

Zone A

Existing rural, low

population, sparsely

developed area

Minimal future population

growth and development

Lower risk area



Zone AE - Base Level Study

Existing low to moderate

population

Moderate population growth

and development potential

Lower risk area

Can use as-built drawings,

design plans, field measures

for structures if available

Limited budget for survey, use

field measures

No floodway analysis needed

Base Level Study(Channel geometry approximated, based on

drainage area)



Zone AE – Enhanced Study

Dense population and

urban environment

Moderate to large

population growth and

development potential

Higher risk area

Budget for channel and

structure survey

Floodway analysis

needed

Enhanced Study(Channel geometry obtained by tradition survey

methods)



Zone AE 2-D Analysis

Dense population and urban

environment

Moderate to large population

growth and development

potential

Higher risk area

Flat topography

Detailed risk data needed

Water surface elevation

computed for every grid cell

Delineation of maximum

water surface computed


1-D/2-D Combined

2-D

Area


2-D FEMA Guidance

Please review the Hydraulics: Two-Dimensional Analysis Guidance

Decision Process outlines whether a 2-D model is appropriate:

Standard Engineering Factors to consider

Cell size, computation time, model stability, calibration,

Factors which impact FEMA products

Population density, regulatory floodway, community expertise and

ease of reporting

Technical (qualitative or quantitative assessment)

Will a 2-D analysis (as oppose to 1-D analysis) result in more

accurate flood elevations on NFIP maps given the conditions on

the ground?

Programmatic (qualitative or quantitative assessment)

What are the benefits to the community and property owners

from a 2-D analysis

Sections on Maintenance and Floodway will be more detailed in future

cycles


Method Selection Example 1

City of Grand

Junction in Greene

County, IA

Effective Data

9/1/1996

Current Effective

Zone A

CNMS Status =

Unverified


New Available Data

2011 imagery

available

2010, 2 foot contour

LiDAR available

Google Earth 2016


Factor Evaluation

Factor Evaluation

Budget Limited

PopulationLow population surrounding

existing floodplains

Risk Low risk

Future Low growth expected, existing

farmland areas

Effective Zone A

Hydraulic Structures Low

Gage Data None

Flow Confined, gradually varying


Result: Updated 1-D Steady Zone A Analysis

Current Effective April 19, 2016


Method Selection Example 2

City of Elizabethtown

in Hardin County, KY

Effective Data

8/16/2007

Current Effective

Zone A

CNMS Status =

Unverified


New Available Data

2015 imagery

available

2012, 2 foot contour

LiDAR available

Google Earth 2016


Factor Evaluation

Factor Evaluation

Budget Moderate

PopulationModerate population

surrounding existing floodplains

Risk Moderate risk

Future

Growth occurred, new

subdivision upstream, growth

projected

Effective Zone A

Hydraulic Structures 10

Gage Data None

Flow Confined, gradually varying


Result

Updated 1-D Steady Zone AE Analysis planned

with survey data and floodway analysis


Data Sources


FEMA Map Service Center Cont.


Getting to the GeoPlatform


FEMA GeoPlatform


Risk MAP Portal Statewide floodplains in a single map

Displays the same floodplain as the FEMA

GeoPlatform Map

Phase I: Zone A BFE (43 counties)

1% annual chance BFE

determinations in the A Flood Zones

with a simple click on the stream

centerline

Hydrologic & Hydraulic reports and

models available for download

FIS and Shapefiles also available

Phase II and Beyond

Hydraulic models and BFE

determination available statewide

Depth grids and other RiskMAP

products

Dam safety information

http://watermaps.ky.gov/RiskPortal/


Product and Data Sources FEMA

https://msc.fema.gov/portal

http://fema.maps.arcgis.com/home/is.com/home/

KDOW http://watermaps.ky.gov

http://watermaps.ky.gov/RiskPortal/

KY GIS

http://kygeonet.ky.gov/

USGS

https://waterdata.usgs.gov/ky/nwis/uv/?site_no=380249084295001&PARAmeter_cd=00045

https://waterdata.usgs.gov/ky/nwis/current?group_key=basin_cd&sort_key=site_no&format=html_table&P

ARAmeter_cd=STATION_NM,DATETIME,00045&precipitation_interval=p01h_va,p04h_va,p12h_va,p24h_va,p05d_va

https://streamstatsags.cr.usgs.gov/streamstats/

http://water.usgs.gov/osw/flood_inundation/

NWS

http://water.weather.gov/ahps/

http://www.kymitigation.org/http://www.kymitigation.org/https://msc.fema.gov/portalhttp://fema.maps.arcgis.com/home/is.com/home/http://kygeonet.ky.gov/https://waterdata.usgs.gov/ky/nwis/uv/?site_no=380249084295001&PARAmeter_cd=00045https://waterdata.usgs.gov/ky/nwis/current?group_key=basin_cd&sort_key=site_no&format=html_table&PARAmeter_cd=STATION_NM,DATETIME,00045&precipitation_interval=p01h_va,p04h_va,p12h_va,p24h_va,p05d_vahttps://streamstatsags.cr.usgs.gov/streamstats/http://water.usgs.gov/osw/flood_inundation/http://water.weather.gov/ahps/

Questions?

Mike Greene

Project Manager

[email protected]

859-422-3079

Katherine Osborne

Project Engineer

[email protected]

859-422-3047

data access and engineering modeling - kamm · hydraulic modeling guidance cross sections must be...

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