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LOWER BLACK EARTH CREEK Modeling conceptual stream restoration plans Lauren V. Brown

November 17, 2010

I chose to use my research paper as an opportunity to engage in a modeling exercise to become more

familiar with stream restoration tools. I wanted to learn how to transfer proposed stream restoration

geometries into Hydrologic Engineering Center’s River Analysis System (HEC-RAS) and to model the

hydrological effects of different flood recurrence intervals for two conceptual stream restoration plans.

The goal was not to create a sophisticated model, but to familiarize myself with new software and

modeling processes as well as to assess the limitations of the tools. For the purpose of the modeling

exercise, I chose to use a project I’m currently working on located along Black Earth Creek (BEC) for my

Water Resources Management (WRM) practicum. To begin I will provide some background for the

project by sharing research and methods that were used to develop the stream restoration options. For

the next portion of the paper I will share the process, results and comments from the HEC-RAS modeling

exercise.

PART ONE: STREAM RESTORATION BACKGROUND & DESIGN

The WRM project is located in the Black Earth Creek watershed, in the township of Mazomanie, WI.

Lower Black Earth Creek is currently impounded by an existing dam structure – the Mazomanie Dam -

which was originally installed in 1855 to divert water from BEC into a mill pond, providing power for the

local feed mill. The dam was recently deemed structurally unsound by the Wisconsin DNR and as a

response, they’ve asked the Village of Mazomanie to remove, replace or repair the dam. For the past

year there has been much deliberation by the Village over which course of action to take. As of last

week, November 9th, 2010, the Village finally made the decision to remove the dam with the DNR’s

$400,000 dam removal grant.

The dam and impounded stream length is located on Mr. Fred Wolf’s property. Mr. Wolf has been an

active proponent for removing the dam and restoring the stream, wetland and floodplain within his

property. He is willing to dedicate a portion of his land along BEC for restoration and recreation

including public access and connected hike and bike trails. The Village’s declaration for removing the

dam is a major step towards moving the restoration of Black Earth Creek forward (see Figure 1).

WRM students devoted part of their efforts this summer investigating the impacts of the dam upon the

immediate upstream floodplain and stream, as well as developing stream restoration options (see Figure

4). The Mazomanie dam has impounded BEC for over 150 years. The meandering stream was

straightened, and the width to depth ratio increased. In addition, cultural (post-settlement) soils have

deposited behind the dam creating a wedge effect of accumulated sediments. As field-measured this

summer, the accumulation is roughly six feet deep directly behind the dam - tapering to a foot and a half

near the first upstream meander (see Figure 3).

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Figure 1: WRM Project area and conceptual easement and stream restoration plan by L. Brown

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Figure 2: Stream & floodplain restoration sketch by L. Brown

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Figure 3: Wedge effect of accumulated cultural sediments upstream of dam

Figure 4: Study area and impounded reach of BEC

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Restoring a meandering stream channel within the study reach involves taking up roughly 7.25 feet of

vertical grade change between the existing upstream and downstream elevations by excavating through

the wedge of accumulated sediments behind the dam. To create a relationship between the average

daily water surface elevation in the channel and a 1.5 year flood recurrence bankfull elevation involves

carving into the relatively flat surface of the floodplain. The Public Land Survey records, NRCS soil maps,

and buried wetland (fibric) soils found beneath cultural soils in the floodplain indicate that the study

area was historically a wetland. Further excavation may be required to restore a wetland floodplain,

which typically floods more frequently than the 1.5 year event (0.5-1 year) (see Figure 2).

Two stream restoration options were developed. The first explores emulating the plan and cross-

sectional morphologies found in a BEC reference reach upstream of our study area. Plan geometries

from the reference reach were used to inform the conceptual stream alignment. For example, radius of

curvature (which varied from 50 – 90’) and belt widths (which ranged from 200-250 feet) informed the

plan layout, while width-to-depth ratios (ranging from 12-27) informed stream width and cross-sectional

shape. The valley slope of the reference reach was very similar to the area of our study reach (roughly

0.3%); therefore I chose a similar channel slope (0.16%) (See Figure 5).

Figure 5: Reference reach - plan geometries

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The general goal of the first stream option was to create as much meander in the floodplain area as

possible to take up the 7.25 foot grade differential. I began upstream, at the southeast corner of the

site, drawing a high sinuosity, low gradient stream in the floodplain. The 0.16% slope was not sufficient

to take up the grade difference however, and a straighter, steeper reach with a 0.625% slope was used

to transition to BEC below the dam. This transition fits well with the existing conditions, as the

floodplain is more constricted by the presence of the dam and retaining wall structure to the southwest

and the steep slope to the farm fields to the northeast. In contrast, the wider area between the existing

railroad berm and farm fields in the majority of the study area seems to be an ideal location for a wide,

flat, wetland floodplain. In order to allow for increased inundation of the wetland floodplain in this

area, bankfull was designed to be roughly one foot above the average water surface (see Figure 6).

Channel length for stream option A is 3000 feet (2400 lf @ 0.152% and 600 lf @ 0.625%).

Figure 6: Stream Option A - Hand-drawing by L. Brown (n.t.s.)

In stream restoration option B I explored a steeper, single gradient stream with less meander and

greater riffle-pool sequences. Stream Option B has a channel slope of 0.3% and a channel length of

2500 ft. Top of bank was established at 1.2 feet above daily average water surface (see Figure 7).

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Figure 7: Stream Option B - Hand-drawn sketch by L. Brown (n.t.s.)

PART TWO: STREAM MODELING

For the purpose of this research topic, I thought it would be interesting to model the response of stream

restoration Option A and Option B to hydraulic flows based upon common recurrence interval flood

discharges such as the 1, 1.5, 2, 10, 100, 200 and 500 year floods. The goal was to compare the

floodplain’s response to the discharges between the two stream options using HEC-RAS. To do so

required inputting the hand-drawn geometric data into HEC-RAS.

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STEP ONE: DISCHARGE VOLUMES

The first step was to gather the discharge data for the lower Black Earth Creek flood recurrence

intervals. Luckily, I already completed this step as part of an earlier homework assignment using peak

flow data derived from gauge station information at BEC near Black Earth, WI. (Discharges for the

recurrence intervals are shown in the chart below.) In addition to flood recurrences, I needed a base

flow discharge for the stream in order to test my stream cross-sections. The chart below shows the

daily discharges in cubic feet per second (cfs) for BEC at the Black Earth gauge station. It appears that

average discharge has increased since the 1950s, with an approximate average of 35 cfs in the latest

period between 1994 and 2006. I therefore chose to use 35 cfs as the profile for the base flow in the

HEC-RAS model. It is interesting, however, to note a jump in daily discharges after 2007, with the lowest

daily discharges mostly exceeding 20 cfs, whereas in the period between 1955 and 1970 the daily low is

closer to 6-7 cfs.

Recurrence 1 yr 1.5 yr 2 yr 10 yr 100 yr 200 yr 500 yr

Discharge (cfs) 55.8 325.7 445.4 1023 1838 2215 2426

Figure 8: BEC daily discharge at Black Earth, WI gauge station

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STEP TWO: DIGITIZING THE HAND-DRAWINGS

The next step involved digitizing the hand-drawn information into a format that could be used by the

modeling programs. The hand-drawings were traced over two-foot contours made available courtesy of

Dane County 2009 Fly Dane aerial survey and printed from ArcGIS. Proposed contours in half foot

intervals were interpolated and hand-drawn based upon the proposed stream alignment, desired bank-

full height and desired floodplain dimensions. The first step in the process was to scan the 24x36 inch

trace paper hand-drawings with a large format scanner. The second step was to digitize the contours.

This was achieved by exporting the two-foot contours from the ArcGIS shape file. The contours were

clipped to the study area and exported into a .dwg or AutoCAD format using ArcGIS Toolbox’s ‘export to

CAD’ conversion tool. This essentially exported the polyline data into a format readable by Autodesk’s

AutoCAD software, maintaining the spatial coordinates and polyline elevations.

The scanned hand-drawings were then inserted into the AutoCAD file and spatially referenced to the

contour data by aligning parcel lines exported from GIS. The proposed contours were then traced or

digitized into AutoCAD, connecting to existing contours at the edges of the study area. Clipped existing

contours were erased, so that the new plan represents only the proposed floodplain elevations. The

proposed stream alignment was also digitized including the stream centerline, 100 ft station nodes, and

left and right bank lines. After digitizing new data was completed, the file was saved to AutoCAD

version 2007 for compatibility and given a coordinate system by importing the coordinates from the

original Fly Dane contour shape file (see Figure 9).

Figure 9: Digitized stream alignment and contours re-imported into ArcGIS

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STEP THREE: CONVERTING GEOMETRIES TO HEC-RAS FORMAT USING HEC-GEORAS

The next step was to import the geometries for the stream and proposed surface of the floodplain into

HEC-RAS. Luckily, a tool was created just for this purpose. HEC-GeoRAS is an extension of the HEC-RAS

software that provides specific tools for converting and importing data from ArcGIS to HEC-RAS readable

layers. HEC-GeoRAS creates an .sdf file of geometric data for import into HEC-RAS from ArcGIS features

such as stream centerlines and bank polylines. HEC-GeoRAS also requires a digital terrain model (DTM)

for the floodplain surface represented by a triangular irregular network (TIN) or a GRID (USACE, 2009).

My digitized contours did not represent a complete 3-dimensional surface, just two-dimensional

polyines with single elevations. However, the contours could be used to interpolate a TIN surface.

ArcGIS’s toolbox contains a 3D analyst tool that can create a TIN from contours and therefore allowed

me to create the needed surface. At first the model showed strange dips along the stream. This was

caused by the presence of the stream bank and centerline (with elevation 0) on the contour layer.

Separating the stream polylines from the contour layer solved the TIN modeling problem as well as

made it simpler to define the Geo Ras layers (see Figure 10).

Figure 10: TIN Model - interpolated from stream contours Option B

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HEC-GeoRAS is displayed as a toolbar feature in ArcGIS. After creating the TIN and separating the

stream bank and stream centerline polylines, the next step was to create the GeoRAS layers. GeoRAS

creates a personal geodatabase (.mdb) file and allows you to create all the layers at once or individually.

Only four layers are required for the model and include: river (stream centerline), banks (both left and

right banks, flow lines (equivalent of stream centerline and left and right banks) and section cuts.

Geometric information can either be created in ArcGIS using the Editor toolbar, or imported from other

shape files. In my case, since the stream information had already been drawn in AutoCAD and

converted to GIS, I chose to import the data. This involved using ArcCatalog to select the features within

the .mdb file and import the data from the stream banks and centerline files I previously created. Cross-

sections were created in ArcGIS by using the pencil editor tool and must be drawn from left bank to right

bank and from downstream to upstream. For the sake of time, I chose to cut eight sections for each

stream option. After populating the RAS layers with the geometries and assigning them HydroID’s

(required and automated by a button) the next step was to run through a list of RAS commands that

automatically converted the GIS data to a HEC-RAS format. This involved specifying the TIN model,

which most importantly was used to define the elevations of the stream banks and interpolation of the

cross-sections. The end product is an .sdf file, a file legible as geometric data in HEC-RAS. .sdf files

were created for both stream Option A and Option B (see Figure 11).

Figure 11: HEC-GeoRAS toolbar, screen capture in GIS of Option B and cross-sections

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STEP FOUR: IMPORTING & MODIFYING GEOMETRIC DATA IN HEC-RAS

Separate HEC-RAS projects were created for stream Option A and Option B. ArcGIS stream geometries

and cross-sections were then imported into HEC-RAS within the geometric schematic window. The

resulting import shows the meandering stream center line, cross-sections, and the locations of the bank

lines (indicated by the red dots) (see Figure 12).

Figure 12: Geometric Data imported into HEC-RAS from GIS .sdf file

The TIN model however did not contain the in-stream cross-sections, as only water surface and bank

elevations were determined. The profile of the stream bed profile however is an important piece of

information in the HEC-RAS model which determines the stream cross-sectional area, and therefore its

capacity to transport different volumes or discharges of water. To add the stream cross-sections, I

referred to BEC channel cross-sectional data that was field-surveyed this summer with Samantha

Greene (see Figure 13). Sam and I measured stream cross-sections at the meander crest and upstream

and downstream arms in our reference reach. I used this information as the benchmark for determining

stream maximum, mean and minimum water depths, as well as cross-section shape in HEC-RAS.

Within the cross-section dialog box of HEC-RAS I was able to manipulate the in-stream cross-sections by

hand by clicking on the points and dragging them (see Figure 14). More accurate depths of certain

points could be given using the cross-section table (see table below that was used to determine cross-

section values). Within this window, I was also able to select bank points and insert a roughness

coefficient of 0.05 outside of the banks and 0.035 within the channel.

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Figure 13: BEC Reference Reach field surveyed cross-sections (summer 2010)

Reach/ Station

Water Surface Max. Depth Mean Depth Min. Depth Reference

A-1 776 774.23 774.82 775.34 Meander Arm DN

A-2 777 775.23 775.82 776.34 Meander Arm DN

A-3 778.5 775.83 777.11 777.88 Meander Crest

A-4 779 776.43 777.47 778.55 Meander Arm UP

A-5 780 778.23 778.82 779.34 Meander Arm DN

A-6 781.05 778.38 779.66 780.43 Meander Crest

A-7 781.5 779.73 780.32 780.84 Meander Arm DN

Reach/ Station

Water Surface Max Depth Mean Depth Min Depth Reference

B-1 775.5 772.83 774.11 774.88 Meander Crest

B-2 776 773.43 774.47 775.55 Meander Arm UP

B-3 777 774.33 775.61 776.38 Meander Crest

B-4 778 775.33 776.61 777.38 Meander Crest

B-5 779 776.33 777.61 778.38 Meander Crest

B-6 780 778.23 778.82 779.34 Meander Arm DN

B-7 781 779.23 779.82 780.34 Meander Arm DN

B-8 781.5 778.93 779.97 781.05 Meander Arm UP

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Figure 14: HEC-RAS Cross-section Editor screenshot

STEP FIVE: MODELING THE FLOW DATA

After modifying the stream cross-sections, the next step was to add the flow data. I originally entered

seven profiles for the flood recurrence intervals for the 1, 1.5, 2, 10, 100, 200 and 500 year floods using

data derived from the gauge station peak flow information (see chart in step 1). For the boundary

conditions I used a normal depth with a slope of 0.003. This was an average slope at the downstream

portion of the stream (1200 linear feet from contour 775.5 to 772 = 0.0029). A subcritical flow was

modeled. Boundary conditions were recommended by Water Resources Engineering Graduate Student

Chad Heimerl who previously modeled the existing conditions for BEC.)

Upon modeling and observing the cross-sections, I realized that I also needed to model the base flow to

determine if the cross-sections were approximated well. At this point I entered an eighth profile for the

35 cfs base flow and found that most of my cross-sectional areas were too large – the modeled water

surface at base flow was lower than what I intended. This required me to manually manipulate the

cross-sections again by trial and error to achieve the desired water surface elevations at base flow. (due

to time, I only was able to modify x-sections in Option B).

After updating the cross-sections so that they represented base flow, I then ran the model again to see

how the other flood recurrence intervals behaved in the proposed surface of the excavated floodplain.

The 1.5 year flood recurrence exceeded the channel bank, spilling into the wetland floodplain as

intended (see Figure 17). The 100 year flood recurrence was contained mostly within the northern berm

of the property owner’s fields and spilled into some of the eastern fields as expected. I was surprised

however to see the flood overtop the railroad berm (see Figure 18). Some problems with the model

however became apparent immediately. For example the model does not appear to run the flow

through the stream channel first but through the entire cross-section. Cross-section 4 cuts through not

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only the stream, but two exposed groundwater depressions in the floodplain. The cross-section view of

the model shows how the flow fills all of the depressions to an even level versus filling the stream

entirely before it spills into the floodplain (see Figure 15). In addition, the x-y-z perspective plot shows

the water surface extending entirely across the floodplain at this section, not just in the low lying

depressions. It also shows how HEC-RAS models at the cross section locations only and does not

interpolate between cross sections. Thus you see straight lines connecting the cross section water

surfaces, resulting in a segmented surface of the flood area. Cutting a greater number of cross-sections

would improve the accuracy (see Figure 16).

Although time limited my ability to fulfill the original research question to compare the floodplain

behavior of Option A and B under similar discharges, I felt I accomplished my goal to familiarize myself

with the software, and was surprised and pleased with the amount I accomplished. The data is now

available for further modeling under a stream restoration expert’s guidance; and with the Village of

Mazomanie’s recent approval to remove the dam; the project is closer to reality.

Figure 15: Option B, X-section 4, base flow (35cfs)

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Figure 16: Option B, Base flow (35 cfs), x-y-z perspective plot

Figure 17: Option B - 1.5 year recurrence interval (35 cfs)

2472.799

2252.015

1880.368

1639.549

1289.178

823.6736

511.0740

BEC_OptB Plan: RunB2 11/16/2010

Legend

WS daily avg

Ground

Bank Sta

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I'd like to acknowledge Chad Heimerl for his guidance in ArcGIS and HEC-RAS and Sam Greene for stream

and floodplain field surveying.

Sources:

US Army Corps of Engineers (USACE), Hydrologic Engineering Center, HEC-GeoRAS GIS Tools for support of HEC-RAS

using Arc GIS, User’s Manual, Version 4.2, September 2009.

Figure 18: Option B - base flow on top of 100 year recurrence interval