Alabama Irrigation InitiativeEnvironmental Meeting

10/31/2008

Ecological Approach

• Original approach was to statistically analyze volumetric withdrawals.

• Ecologically, the area of inundation is potentially just as important as volumetric flow

• Revised approach to analyze total flood plain affected by withdrawals

Center for Freshwater Studies Area of Interest – Sipsey River Swamp

Approach

USGS Historic Data & Rating Curves

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

0 1000 2000 3000 4000 5000

Interpolated Gage Height

Actual Gage Height

Rating CurveRating curve based on USGS dataRelates discharge (known) to gage height (needed)

• USGS provides table of Discharge versus Gage Height

• Estimated gage height in region of interest (approximately 4.5 miles downstream of Elrod station)

• Interpolation routine for Rating data is statistically accurate.

• Currently have rating data 11 & 12 (1995 – present).

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

0 1000 2000 3000 4000 5000

Interpolated Gage Height

Actual Gage Height

Area of Interest – GIS Model

GIS Area Model

ArcGIS Area Data

• Similar to the Rating Curve table, the “Area Curve” table is used to estimate the area of inundation from a “synthetic” withdrawal.

• The interpolation routine for area data is accurate.

0.00

2000.00

4000.00

6000.00

8000.00

10000.00

12000.00

14000.00

16000.00

-20.00 -10.00 0.00 10.00 20.00 30.00 40.00

Gage Height (above 185.66')

Acr

es Area (acres)

Interpolated Area (acres)

Statistical Analysis Method

• The Wilcoxon Rank-Sum test is used– The Wilcoxon rank-sum

test is a nonparametric alternative to the two sample t-test

– The null hypothesis is that the means of the two samples are statistically equal.

– If the shift is greater than the confidence level (α). For a two-tailed test (A=B versus A≠B), confidence level is α/2

Statistical Analysis Spreadsheet 365 vs. 120 day analysis

2001 365-day Analysis

• Before withdrawal in orange (burnt?)

• After withdrawal in blue (39.5% of discharge withdrawn)

• This was the highest flow day during withdrawal period (January through April)

2001 120-day Analysis

• Before withdrawal in orange…

• After withdrawal in blue (16.7% of discharge withdrawn)

• This was the highest flow day during withdrawal period (January through April)

Approximate Area before/after Synthetic Withdrawal

0.00

1000.00

2000.00

3000.00

4000.00

5000.00

6000.00

7000.00

8000.00

9000.00

10000.00

1 19 37 55 73 91 109 127 145 163 181 199 217 235 253 271 289 307 325 343 361

Area of inundation BW (acreas)

Area of Inundation AW (acres)

Discharge (cfs)

Discharge AW (cfs)

• Withdrawal set at 12% of discharge.• That equates to 44225 acre-ft• Withdrawal period is Jan-April 1995 (Rating

Curve 11)

Year Total Withdrawal (acre-ft)

1995 44,225

1996 50,466

1997 45,025

1998 53,154

1999 47,435

2000 29,458

2001 65,731

2002 44,230

2003 55,296

2004 69,879

2005 31,039

2006 60,150

2007 35,963

2008 41,419

   

Average= 48,105

Max= 69,879

Min= 29,458

Scaling Up to the AL and TN RiversPercent Withdrawan Year Total Acre Feet

12.00% 1995 1,429,140

12.50% 1996 2,059,965

13.00% 1997 1,891,070

10.50% 1998 2,163,854

11.00% 1999 937,516

8.70% 2000 541,633

16.65% 2001 2,419,211

15.70% 2002 1,138,976

12.90% 2003 1,543,614

17.85% 2004 1,202,672

11.30% 2005 1,395,497

15.05% 2006 1,239,750

19.25% 2007 862,494

19.90% 2008 960,040

   

  Average= 1,413,245

  Max= 2,419,211

  Minimum= 541,633

Percent Withdrawan Year Total Acre Feet

12.00% 1995 1,533,024

12.50% 1996 2,163,887

13.00% 1997 2,296,935

  1998  

  1999  

8.70% 2000 643,248

16.65% 2001 1,347,570

15.70% 2002 1,584,510

12.90% 2003 1,841,181

  2004  

11.30% 2005 1,344,564

  2006  

  2007  

  2008  

   

  Average= 1,594,365

  Max= 2,296,935

  Minimum= 643,248

Alabama River - Claiborne Tennessee River - Whitesburg

Perspective

• The minimum available water from the AL and TN rivers could irrigate ~1,000,000 acres.

• That is approximately ~3% of the total area of Alabama

Conclusions/Issues

• Basing withdrawals on the cyclic inundation of a floodplain attempts to take the river ecology into account

• The method shows that statistically insignificant fractions are available that are within the total, annual variability of the river

• Each river is unique and analysis may have to be modified to account for different channel/floodplain characteristics