Runoff Volume Controls in Harris County, Texas

Sustainable Urban Water Workshop June 4, 2015

Burton L. Johnson, PE, CFM

Burton Johnson Engineering, Inc.

North Texas LID Competition - 2012

Northwest Crossing • Mixed use

Residential/Commercial • Large site • Highly impervious soils • Aggressive prairie

restoration to control volume

Cypress Creek Overflow Management Plan

• Project Sponsor – Harris County Flood Control District – Texas Water Development Board

• Project Team – Burton Johnson Engineering – Michael Baker International – SWA Group – Mitigation Resources

Upper Cypress Creek and Addicks Watersheds

Study Area = 277 square miles

Cypress Creek Overflow Management Plan – Study Area

• Harris County Flood Control District

• Harris County Public Infrastructure Department

• Harris County Precinct 3 • Harris County Precinct 4 • City of Houston

• Waller County • Corps of Engineers • Bayou Preservation

Association • Katy Prairie Conservatory • West Houston

Association

Steering Committee

Early Houston Floods

1929

1935

1940 Corps Project Plan

1940 Corps Project Plan

• Addicks, Barker, and White Oak Reservoirs – Addicks and Barker ungated – Peak combined discharge of 15,700 cfs

• Cypress Creek Levee • Brickhouse Gully Bypass • North and South Canals

1940 Corps Project Plan

• Addicks, Barker, and White Oak Reservoirs – Addicks and Barker ungated gated – Peak combined discharge of 15,700 cfs

6,000 cfs 2,000 cfs (@ Piney Point gage)

• Cypress Creek Levee Increased Addicks land acquisition

• Brickhouse Gully Bypass • North and South Canals Buffalo

Bayou Channel Improvements

Un-gated Conduits

April 27, 1944

Gating of Conduits

Barker Gate

Flow at Piney Point <2,000 cfs •Addicks Release •Barker Release •Local Flows Piney Point Gage 9 miles DS

1944

2003

Current Development Around Addicks Reservoir

Current Development Around Barker Reservoir

4

3

2 1

5

Location Elev (ft)

Approx. Return Interval

1 – SH 6 96 5-Yr

2 – Eldridge Pkwy 97 12-Yr

3 – Clay Rd 92 2-Yr

4 – Patterson Rd 90 <2-yr

5 – Westhemier Pkwy 93 20-yr

Addicks Reservoir Trends

1977 Hydrology Study

The “Ratcheting Effect” – 1991-1992 Event (1973 datum adj) Pool Elevations

0

2

4

6

8

10

12

70

75

80

85

90

95

100

105

110

12/21 12/26 12/31 1/5 1/10 1/15 1/20 1/25 1/30 2/4 2/9 2/14 2/19 2/24 2/29 3/5

Rain

fall

(inch

es)

Pool

Ele

vatio

n

Date

Rainfall 1992 w 70.8% Runoff 1992 w 80% Runoff 1992 w 90% Runoff 100-year Government Land

The “Ratcheting Effect” – 1991-1992 Event (1973 datum adj) Storage Volumes

0

2

4

6

8

10

12

0

20,000

40,000

60,000

80,000

100,000

120,000

140,000

12/21 12/26 12/31 1/5 1/10 1/15 1/20 1/25 1/30 2/4 2/9 2/14 2/19 2/24 2/29 3/5

Rain

fall

(inch

es)

Stor

age

Volu

me

(ac-

ft)

Date

Rainfall 1992 w70.8% Runoff 1992 w80% Runoff 1992 w 90% Runoff 100-year Government Land

Non “Ratcheting” Event – 2009 Event (1973 datum adj) Pool Elevation

0

2

4

6

8

10

12

70

75

80

85

90

95

100

105

110

4/16 4/17 4/18 4/19 4/20 4/21 4/22 4/23 4/24 4/25 4/26 4/27 4/28 4/29 4/30

Rain

fall

(inch

es)

Pool

Ele

vatio

n

Date

Rainfall 1992 w 70.8% Runoff 1992 w 80% Runoff 1992 w 90% Runoff 100-year Government Land

Extrapolate to Estimate 75-day Rainfall Depth

Rainfall from TP-40 and TP-49 used to develop trendline equations

Estimate 1991-92 75-day Rainfall to Approximate a 38-year event

The “Ratcheting Effect” – 1991-1992 Event Rainfall Increased to Simulate 100-yr Event

Pool Elevations

0

2

4

6

8

10

12

70

75

80

85

90

95

100

105

110

12/21 12/26 12/31 1/5 1/10 1/15 1/20 1/25 1/30 2/4 2/9 2/14 2/19 2/24 2/29 3/5

Rain

fall

(inch

es)

Pool

Ele

vatio

n

Date Rainfall 1992 adj to 1% w 82% runoff 1992 adj to 1% w 90% runoff1992 adj to 1% w 100% runoff 100-year Government Land

• Development policy requires detention basins to offset increase in peak runoff..

• Detention addresses “flow” more than “volume”.

Development Volume Impact

• Region 1 – 0% to 40%, impact is 1.8 inches

• Most single family subdivisions - 40% to 50% impervious

• Impact is about 2” of runoff

Effect of Prairie Grass on Runoff Literature Review A Bunch of Googling

• Often cited – native prairie grass increases infiltration capacity of soil

• All citations point back to only two studies – Both studies were related to agricultural impact on soil

infiltration – Compared to native prairie and restored prairie

NRCS Research Sites

Source: Fennessey, Miller, and Hamlett

Town State Stations/ Watersheds

Land Use Used for CN?

Amot Forest New York 2 Idle, wooded

College Park Maryland 4 Pasture, Wooded

Watkinsville Georgia 1 Pasture

Statesville North Carolina 1 Wooded

Edwardsville Illinois 1 Pasture Yes

Elmwood Illinois 6 Pasture

Lafayette Indiana 6 Pasture, Wooded

East Lansing Michigan 1 Wooded

Bethany Missouri 3 Pasture

Coshocton Ohio 8 Pasture, Wooded, Meadow Yes

Hamilton Ohio 1 Pasture Yes

Zanesville Ohio 2 Pasture, Wooded

LaCrosse Wisconsin 2 Pasture

Bentonville Arkansas 3 Pasture, Wooded Yes

Guthrie Oklahoma 4 Wooded, Idle, Pasture

Muskogee Oklahoma 1 Pasture Yes

Stillwater Oklahoma 1 Rangeland

Garland Texas 1 Meadow Yes

Tyler Texas 2 Pasture, Wooded

Vega Texas 2 Pasture Yes

Hays Kansas 1 Pasture

Hastings Nebraska 3 Pasture, Meadow Yes

NRCS Curve Numbers Cover Description Hydrologic Soil Group

Cover Type Hydrologic Condition A B C D

Pasture, grassland, or range-continuous forage for grazing

Poor Fair Good

68 49 39

79 69 61

86 79 74

89 84 80

Meadow-continuous grass protected from grazing and generally mowed for hay

Good 30 58 71 78

Brush-brush-forbs-grass mixture with brush the major element

Poor Fair Good

48 35 30

67 56 48

77 70 65

83 77 73

Woods-grass combination (orchard or tree farm) Poor Fair Good

57 43 32

73 65 58

82 76 72

86 82 79

Woods Poor Fair Good

45 36 30

66 60 55

77 73 70

83 79 77

Herbaceous-mixture of grass, weeds and low-growing brush, with brush the minor element

Poor Fair Good

80 71 62

87 81 74

93 89 85

Sage-grass-sage with an understory of grass Poor Fair Good

67 51 35

80 63 47

85 70 55

Preliminary Conclusions

• Research suggests that native prairie has substantially better absorption capability, even in “poorly draining” soil

• Agricultural activity (row crops, grazing) has a substantial and adverse impact to soil infiltration

• Prairie restoration has the potential to notably increase soil infiltration – estimate a 1:1 development/mitigation ratio

• More study desired – HCFCD engaged Mitigation Resources, LLC to study in greater detail

Prairie

Open Space

Developed Property

Each site is equipped with a monitoring station

All runoff flows through a known

discharge point

Measurements include:

Rainfall Runoff Groundwater

Using these measurements, the

volume of runoff storage for the site can be calculated

Monitoring station Runoff Discharge

Point

Investigation of Prairie Restoration for Flood Control

-

1

2

3

4

5

March 10,2013

April 2, 2013 April 27, 2013

Developed Average Absorption 39%

Investigation of Prairie Restoration for Flood Control

-

1

2

3

4

5

March 10,2013

January 8,2013

April 27, 2013

Open Space Average Absorption 77%

-

1

2

3

4

5

March 10, 2013 April 2, 2013 April 27, 2013

Native Prairie Average Absorption 88%

Inch

es

Absorption (in) Runoff (in) Rainfall (in)

Reducing the Curve Number: Decreased Volume of Runoff Increased Infiltration Capacity

**Development impact can be offset in part by restoring Native Prairie

0

25

50

75

100

Native Prairie Open Space Developed

Calculated Curve Numbers by Land Cover Type

53

73

87

Native Prairie Open Space Developed Residential/Commercial

97

Investigation of Prairie Restoration for Flood Control

• Require developments to manage the increase in runoff volume, just as they do the increase in flow rate

• Options – Retention of first 2” of runoff (can be released if

reservoirs are not threatened) – Prairie restoration – Re-use of first 2” of runoff – Low Impact Development – Other, subject to HCFCD approval

• Currently working with engineering and development community to implement

General Strategy- Policy

Why is Retention Needed in Upper Cypress Creek

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

0 20 40 60 80 100 120

Flow

Rat

e (c

fs)

Time (hrs) Existing OF Developed OF Detention OF

No increase in peak OF flowrate, but increaese in duration of overflow results in increased volume

Stormwater Volume Control

• Initial Resistance – Just don’t want to! • Lack of Understanding

– Need agreement on problem before consensus on solution! – Multiple workshops (Greater Houston Builders Association,

West Houston Association, ACEC)

• Stakeholder solutions • Flexibility • Variations of Solution

– Regional – Banking – Re-use – “All Clear” signal

l h l!

Implementation of Policy - Challenges

Burton Johnson, PE, CFM burton@bjeengineering.com

281-773-7184