Rush River Assessment ProjectHydrologic Flow Study

Sibley County SWCD

Presentation to the Minnesota River Research Forum

March 10, 2005

Today’s Take Home Messages Well calibrated, less data intensive, and adaptable

watershed response models can be created on reasonable budgets

Accurate modeling hydrologic flows from agricultural watersheds is strongly dependent upon:

Accounting for the landscape’s changing runoff characteristics over the course of the year

Defining the relationship among surface flow, flow into tile intakes, and subsurface flow (good monitoring data required)

Retention storage is the key to reducing flows in the Rush River

Where’s the Rush?

The Rush River Watershed is one of six subwatersheds within the Lower MN River Subwatershed

Goal: Locate storage areas within watershed to alter peak flowsHydrologic Study was part of the RRAP

which had the goal of determining:

Pollutant sources and amounts

Actions necessary to reduce pollutant levels to obtain water quality standards and designated uses

Actions to reduce river flows

The RRAP involved extensive monitoring

Project constraints revolved around budget and scale

The budget and scale allowed: USGS topographic maps

Ditch cross-sections and crossing elevations

Culvert and bridge plans

Flow monitoring – Scott Matteson RRAP Coordinator

Project constraints revolved around budget and scale

Project constraints revolved around budget and scale

The budget and scale did not allow:

Tile sizes, location and capacity

Smaller tributary ditches and crossings

2’ or better topographic information

Even if we had the data we could not have used it effectively

XP-SWMM: A sewer model goes ag Why use SWMM?

Hydraulics are important

Hydrologic capabilities are in same interface

It accounts for ditch storage

XP-SWMM: A sewer model goes ag Model structure

Conduits

Nodes

XP-SWMM: A sewer model goes ag Model statistics

165 discrete channels and culverts, 142 nodes

977,266 feet / 185 miles

1.4 billion cu. ft. storage in channels

560 million cu. ft. storage in basins

Furthest upstream ditch: 1042 MSLRush River at Minnesota River: 720 MSL

Some hydrologic parameters had to be assumed

Simplifying assumptions

Flood simulation: SCS composite CN = 75

One tile intake per 33 acres

Minimal retention on landscape

Chart 3.2Hydrological Flow Comparison

0

100

200

300

400

500

600

700

800

900

1000

0 10 20 30 40 50 60 70 80

Time (Hours)

Flo

w (

cfs)

Non-Tiled Runoff (cfs)

Tiled Runoff (cfs)

Land Use Acreage Percent of Total

Cultivated Land 232,337 90

Woodland/Forest 9,272 4

Urban Rural Development

5,804 2

Grassland 4,005 2

Wetland 2,561 1

Water 1,899 1

Conservation Land

1,821 1

Other 77 0

Total 257,775 100

The “Design Storms” required adjustment

Area to point rainfall relationships are important

Rush River watershed is 400 sq. miles 9% reduction

in 24-hour point rainfall

45% reduction in ½-hour point rainfall

Areal to Point Rainfall RelationshipsVarious Storm Durations

From Bulletin 71, Huff and Angel

50%

55%

60%

65%

70%

75%

80%

85%

90%

95%

100%

0 50 100 150 200 250 300 350 400

Area (Square Miles)

Per

cen

t o

f P

oin

t R

ain

fall

0.5 1 2 3

6 12 24 48

Hydrologic assumptions tested against monitoring data in a iterative process Sites monitored in 2003

Compare monitored flows to modeled flows to discover limitations

Hydrologic assumptions tested against monitoring data in a iterative process Correlation #1

assumptions

Five RRAP rain gauges

1 tile intake per 33 acres

10% direct surface connection to ditches

SCS average CN = 75

Chart 3.3RP5 Guaging Station

Comparison of Monitored versus Modeled Flows

0

200

400

600

800

1000

4/1/2

003

4/8/2

003

4/15

/2003

4/22

/2003

4/29

/2003

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003

5/13

/2003

5/20

/2003

5/27

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003

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/2003

6/17

/2003

6/24

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003

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7/29

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003

8/12

/2003

8/19

/2003

8/26

/2003

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003

9/9/2

003

9/16

/2003

9/23

/2003

9/30

/2003

Date

Flo

w (

cfs)

Modeled

Monitored

Chart 3.4RP1 Gauging Station

Comparison of Monitored versus Modeled Flows

0

600

1200

1800

2400

3000

4/1/2

003

4/8/2

003

4/15

/2003

4/22

/2003

4/29

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003

5/13

/2003

5/20

/2003

5/27

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003

6/10

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6/17

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6/24

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003

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7/15

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7/22

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7/29

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8/5/2

003

8/12

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8/19

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8/26

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9/2/2

003

9/9/2

003

9/16

/2003

9/23

/2003

9/30

/2003

Date

Flo

w (

cfs)

Modeled

Monitored

Hydrologic assumptions tested against monitoring data in a iterative process Correlation #2

assumptions

Five RRAP rain gauges plus 5 additional rain gauges

1 tile intake per 33 acres

10% direct surface connection to ditches

SCS average CN = 75

Hydrologic assumptions tested against monitoring data in a iterative process Correlation #3 assumptions

Five RRAP rain gauges plus 5 additional rain gauges

1 tile intake per 33 acres

10% direct surface connection to ditches

SCS average CN = 75

Separation of drainage areas into quick and lagging runoff components

Chart 3.7RP1 Guaging Station

Comparison of Monitored versus Modeled Flowswith Area Distribution Calibration

0

600

1200

1800

2400

3000

4/1/2

003

4/8/2

003

4/15

/2003

4/22

/2003

4/29

/2003

5/6/2

003

5/13

/2003

5/20

/2003

5/27

/2003

6/3/2

003

6/10

/2003

6/17

/2003

6/24

/2003

7/1/2

003

7/8/2

003

7/15

/2003

7/22

/2003

7/29

/2003

8/5/2

003

8/12

/2003

8/19

/2003

8/26

/2003

9/2/2

003

9/9/2

003

9/16

/2003

9/23

/2003

9/30

/2003

Date

Ave

rage

Dai

ly F

low

(cf

s)

Monitored

Modeled

Hydrologic assumptions tested against monitoring data in a iterative process Correlation #4

assumptions

Separation of drainage areas into quick and lagging runoff components

Use of changing CN through the season

Season ConditionSCS Curve Number

Runoff Depth for 5.4-inch Rainfall

Spring Fallow 86 3.8

Summer Average 75 2.8

Late Summer/Fall Mature 64 1.8

Hydrologic assumptions tested against monitoring data in a iterative process Correlation #5 assumptions

Use of changing CN through the season

Use of storage instead of quick and lagging runoff components for drainage areas

Goal: Locate storage areas within watershed to alter peak flows Originally pursued track of single large

projects Problem: feasibility and upstream impacts Problem: dozens of projects needed

Revised track is programmatic approach – subwatershed by subwatershed 5% / 40% 10% / 80%

Goal: Locate storage areas within watershed to alter peak flows Where are the restorable surface waters -

everywhere

Goal: Locate storage areas within watershed to alter peak flows

Existing

Conservation

5/40

10/80

Goal: Locate storage areas within watershed to alter peak flows

Reach

Existing Conservation 5% Wetland/Storage 10% Wetland/Storage

(ac-ft) (ac-ft) (%) (ac-ft) (%) (ac-ft) (%)

North Branch 27,100 18,200 67.2% 8,800 32.5% 2,600 9.6%

Middle Branch 24,100 16,100 66.8% 7,700 32.0% 2,300 9.5%

North Fork, South Branch 23,000 15,700 68.3% 7,600 33.0% 2,200 9.6%

South Fork, South Branch 21,600 14,600 67.6% 7,000 32.4% 2,100 9.7%

Rush River Mouth 110,900 74,700 67.4% 36,000 32.5% 10,600 9.6%

Average Annual Flow Volume Comparison

Goal: Locate storage areas within watershed to alter peak flows

100-Year Event Comparison

Reach

Existing Conservation 5% Wetland/Storage 10% Wetland/Storage

(cfs) (cfs) (%) (cfs) (%) (cfs) (%)

North Branch 1,707 1,257 74% 765 45% 265 16%

Middle Branch 4,153 3,268 79% 2,129 51% 611 15%

South Branch 4,716 4,565 97% 2,817 60% 808 17%

Rush River Mouth 9,085 8,042 89% 5,097 56% 1,458 16%

What do you do when the basin is filled?

Basin Design Criteria

•Watershed to basin area of 8 to 1•Average bounce of 2.5 feet•Retention equivalent to runoff from 100-year rainfall•Evaporation and infiltration as only outlets•Possible inclusion of valved drawdown (not modeled)

100%

90%

80%

70%

60%

50%

40%

30%

20%

10%

0%

0

0.5

1

1.5

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2.5

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3.5

4

4.5

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Date

% o

f B

asin

Sto

rag

e U

tili

zed

Pre

cip

itat

ion

(in

ches

)

Storage w/Evaporation

Storage w/Evap. & Infiltration

Precipitation

Where are the areas of focus for restoration activity?

What should the restoration goal be?

Looking beyond the Rush River Assessment Project

Identify funding sourcesUSFWSStateClean Water

PartnershipPrivate entities

Identify, assess, and implement pilot project

Summary

Model correlation is a must but it can be done using sound hydrologic concepts – i.e with less data.

Good monitoring data allowed us to acccurately reflect the changing landscape conditions and the relationship between surface and subsurface drainage.

Mitigation strategies emphasize the programmatic approach rather than the big project approach and emphasize retention and not rate control.