# Presentation: 936331

## The Turkey Creek Hydrologic Study

- Using HEC-HMA and HEC-RAS to simulate the hydrology and flooding of the Turkey Creek
- GIS data sets and general modeling
- HEC-HMS (GIS, watersheds, and routing)
- HEC-RAS (Flood Modeling and Hydraulics)

**Notes:**
The Swan Creek Hydrologic Study involves three objectives.

Understanding trends in urbanization
Understanding Stream Hydraulics
Determining if there is a quantifiable link between Urbanization and Flooding

## Turkey Creek Watershed

## Hydric Soil Groups

## Land Use Classification

## Digital Elevation Model

## Contours

## Stream reaches and outlets

- Stream reaches and outlets

## Detailed Watershed Development

## Improving Land Use Study

- The air photos cane be analyzed into classes that are sensitive to the amount of water that will potentially run off.
- The classes should be developed maintaining Anderson II land use classification system
- 2006 and 2005 air photos are available for the land use analysis

**Notes:**
Each of these types of land uses concentrate water to the creek in different ways.
The Classification is a method of determining percent of impervious ground
Each Land- use Class is Given a Manning Number - roughness

## Determining Flow and Flooding 

- HEC-HMS
- Is a numerical model that simulates watershed channel and control structures to predict flow stage and timing.
- HEC-RAS
- Is used to predict stage, velocities and water profiles for land use and flooding scenarios

**Notes:**
Rational Equation
The Rational Equation is a mathematical formula that lets us combine a rain event with the land-use to approximate the water that will flow to the creek.

 the modification is designed based on the techniques of Rossmiller 1980

## Steps in analyzing flow and flooding

- Rain fall parameters
- Known stream flow
- Type storms

- HEC-HMS

- HEC=RAS

## Generate Stream Network

- Define drainage area

- We can densify it through field work and DEM analysis.

## Water in   Water out

- Precipitation and flow data is used as the inputs to the HEC-HMS system
- Gage records
- Regional watershed basin statistical characteristics
- USGS regression equations

## Hydrologic Analysis – Numerical Modeling [1]

- Precipitation data
- Rain gages
- NEXRAD
- Hyetograph

**Notes:**
One primary required input for numerical hydrologic modeling is precipitation data.  This information is typically collected on the ground by rain gages or by radar such as NEXRAD (Next Generation Weather Radar).

In the computer model, these data are input in the form of a hyetograph, which relates rainfall to time, thereby providing a measure of rainfall intensity.

## Hydrologic Analysis - Output

- Discharge
- Hydrograph
- Peak discharge
- Duration

**Notes:**
The main outputs of hydrologic modeling are flood discharge and timing along a reach, both of which are captured by a flood hydrograph.  Although the timing is important, the output most often applied to further analysis is the peak discharge.

## Develop Hydrologic characteristics

- Determines discharge-frequency relationship for each reach in study region
- Gaged reaches: Derive curves from the USGS Streamflow Basin Characteristics File
- Ungaged reaches: Apply USGS regression equations

- Example discharge- frequency curve from stream gage

## Hydrologic Analysis – Regression

- Problem:  many streams contain no USGS gage data
- USGS solution:
- Identify hydrologic regions with similar climatic and hydrologic characteristics and analyze gage records within the region
- Fit functions of basin characteristics to the peak discharges for a particular frequency at each gage
- Technique called multiple regression analysis
- Results are published functions for over 200 hydrologic regions
- For more information, see “Nationwide Summary of U.S. Geological Survey Regional Regression Equations for Estimating Magnitude and Frequency of Floods for Ungaged Sites.” (USGS, 1993) or browse to http://water.usgs.gov/osw/programs/nffp.html

**Notes:**
Here are some of the most commonly applied stream hydraulic models.

## Hydraulic Modeling HEC-RAS

- given discharge and stream channel morphology, compute flood elevations at cross sections
- Common Methods
- Numerical modeling
- Manning’s Equation

## Hydraulic Modeling – Common Models

- HEC-2 (USACE)
- HEC-RAS (USACE)
- WSPRO (USGS)
- SWMM (EPA)
- MIKE11 (DHI)
- UNET (USACE)

- For more information, visit http://www.floodmaps.net/mit/tsd/en_hydro.htm

**Notes:**
Here are some of the most commonly applied stream hydraulic models.

## Hydraulics – Channel Cross Section

- Cross section
- Channel
- Floodplain
- Friction factors

- Discharge
- Flood elevation
- Velocity

- Floodplain

- Floodplain

- Left Bank

- Flood Water Surface

- Right Bank

- Normal Water Surface

-  Main

-  Channel

- _Inputs_

- _Outputs_

**Notes:**
In hydrologic modeling, the watershed is the base unit of analysis and the computations are performed on a reach by reach basis.  In hydraulic modeling, the reach is the base unit of analysis and computations are performed on a cross-section basis.  The two primary inputs to hydraulic modeling are discharge values and cross-sections descriptions.

The channel is typically divided into components of the main channel and floodplain, which are separated by the stream banks.  During flooding, water spills out of the main channel into the adjacent floodplain.  The behavior of the floodwater is dependent primarily upon  the channel slope, cross-sectional geometry, and friction factors for inundated areas.

## Geo-RAS

**Notes:**
Hec - RAS 3.0 from the Army Corps of Engineers was selected as the flood modeling program for this project. 
The GIS data was is integrated using Geo-RAS a Pre-RAS processor which creates a single Hec-RAS import file
 Necessary information included:
Topography, Stream Reaches, Channel position, Bank positions, Flow Direction, Manning Values, Cross Section Lines

## Land-use and Manning Coefficients

- Each segment of the channel was assigned Manning values based on the cross sections and interpolation of the data.

## Hec-RAS Environment

- Hec-RAS Environment

**Notes:**
The Hec-RAS program is a Windows based modeling environment

Hec-RAS allows stream geometry, Cross section development and both Stead Flow and Unsteady Flow Simulations

## Model Output 25 year Flood

**Model Output 25 year Flood**

## Reintegration of the model into the GIS

- Flooding Through Toledo, Oh

**Reintegration of the model into the GIS**

**Notes:**
Reintegration of the model into the GIS
Allows the display of the flood boundaries with the land use maps, air photos and any other GIS data layers that are available 
Including ReCRA and EPA data sets 

## Flood Modeling Results

- 9

- 7

- 3

- 1

- 9

- 8

- 8

- 1

- 9

- 9

- 5

- The 1973, 1988, 1995 model runs for a P50 storm event , showing the extent of flooding within the watershed along tributaries and stream channels.

**Notes:**
1973 P50 storm now causes flooding equal to a P10 storm in 1995
Smaller more frequent storms presently are flooding the same area as larger less frequent storms 30 years ago
Calibration of the model based on the 1973 P100 storm calculated a difference of 0.11 km2

Mention 50 year is now 10 Year

calibration to 1973 event Confidence in numbers 29 acres different