Green & Ampt or SCS? · The SCS Curve Number method produced generally lower peak flows than Green...

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Green & Ampt or SCS? A Comparison of Hydrologic Methodologies for the City of Mesquite, Nevada September 6, 2017 Andrew Trelease, PE, CFM , Clark County Regional Flood Control District Clark Barlow, PE, CFM, Atkins Travis Anderson, PE, City of Mesquite 25 September 2017 1 Contains sensitive information

Transcript of Green & Ampt or SCS? · The SCS Curve Number method produced generally lower peak flows than Green...

Page 1: Green & Ampt or SCS? · The SCS Curve Number method produced generally lower peak flows than Green & Ampt but runoff volume was generally higher.* Based on this comparison, it was

Green & Ampt or SCS? A Comparison of Hydrologic Methodologies for the City of Mesquite, Nevada

September 6, 2017Andrew Trelease, PE, CFM , Clark County Regional Flood Control District

Clark Barlow, PE, CFM, Atkins

Travis Anderson, PE, City of Mesquite

25 September 2017 1Contains sensitive information

Page 2: Green & Ampt or SCS? · The SCS Curve Number method produced generally lower peak flows than Green & Ampt but runoff volume was generally higher.* Based on this comparison, it was

2017 Flood Control Master Plan Update, City of Mesquite, NevadaProject Overview

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Project Location

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Page 4: Green & Ampt or SCS? · The SCS Curve Number method produced generally lower peak flows than Green & Ampt but runoff volume was generally higher.* Based on this comparison, it was

Master Plan Overview

• Nevada Revised Statute 543.596 requires that flood control master plans must be reviewed and updated at least every 5 years.

• Previous updates in 1991, 1995, 2001, 2007, 2012 for the City of Mesquite

• 2017 MPU facility recommendations are complete; full MPU being finalized

• The purpose of the update (MPU) is to add new information, assess progress, and recommend changes

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Page 5: Green & Ampt or SCS? · The SCS Curve Number method produced generally lower peak flows than Green & Ampt but runoff volume was generally higher.* Based on this comparison, it was

Master Plan Scope

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Recognize/ Identify

Risk

•Data collection and review•Fieldwork•Flood History

Define and Quantify

Risk

• Hydrologic analysis• Hydraulic analysis

Mitigate Risk

• Plan formulation• Cost estimates• Final document/plan and priorities

Page 6: Green & Ampt or SCS? · The SCS Curve Number method produced generally lower peak flows than Green & Ampt but runoff volume was generally higher.* Based on this comparison, it was

Study Area

• Town Wash• Abbott Wash• Pulsipher Wash• Western Washes• Additional Watersheds• Toquop Wash• Virgin River

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Page 7: Green & Ampt or SCS? · The SCS Curve Number method produced generally lower peak flows than Green & Ampt but runoff volume was generally higher.* Based on this comparison, it was

2017 Hydrologic Model Comparison

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Page 8: Green & Ampt or SCS? · The SCS Curve Number method produced generally lower peak flows than Green & Ampt but runoff volume was generally higher.* Based on this comparison, it was

Model Background

• HEC-1 Model• 2007 Model used Green & Ampt Method• The rest of Clark County uses SCS method

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Page 9: Green & Ampt or SCS? · The SCS Curve Number method produced generally lower peak flows than Green & Ampt but runoff volume was generally higher.* Based on this comparison, it was

Overview of Methods

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SCS Curve Number Method Green & Ampt MethodBased on empirical formula Based on conceptual infiltration

modelRelatively easy to apply More difficult to applyDifficult to verify parameters Field verifiableCommonly used Less common

Page 10: Green & Ampt or SCS? · The SCS Curve Number method produced generally lower peak flows than Green & Ampt but runoff volume was generally higher.* Based on this comparison, it was

Goal of Model Comparison

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Determine Most Appropriate Method for City of Mesquite

SCSUpdate models to

be more consistent with the rest of Clark County

Green & AmptUpdate models to

use prescribed methodology

(Mohave County)

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Land Use Changes

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Page 12: Green & Ampt or SCS? · The SCS Curve Number method produced generally lower peak flows than Green & Ampt but runoff volume was generally higher.* Based on this comparison, it was

2007 Hydrologic Soil Group• Data obtained from

2002/2003 NRCS Soil Survey

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Page 13: Green & Ampt or SCS? · The SCS Curve Number method produced generally lower peak flows than Green & Ampt but runoff volume was generally higher.* Based on this comparison, it was

2017 Hydrologic Soil Group• Data obtained from

2014 NRCS Soil Survey

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Changed from C to B

Changed from C to A

Changed from B to C

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2007 XKSAT Green & Ampt• Dark red = higher

infiltration (less runoff)• Yellow = low infiltration

(high runoff)

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2017 XKSAT Green & Ampt – Dense• Follows Mohave County

Method• Uses a uniform soil density

factor of 1.1 for all lad uses (No distinction between undeveloped and developed areas)

• Slightly lower infiltration than in 2007 for most of the area

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Lower infiltration rates

Lower infiltration rates

Higher infiltration rates

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Model Comparison Strategy

Update 2007 Model to use Green & Ampt Method from neighboring Mohave County*

Develop SCS Model using 2017 data and compare

*for model comparison, SCS UH Transform was used for both models

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Page 17: Green & Ampt or SCS? · The SCS Curve Number method produced generally lower peak flows than Green & Ampt but runoff volume was generally higher.* Based on this comparison, it was

Results of Model Comparison

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2007 v. 2017 Green & Ampt – Hydrograph Comparisons

• 2007 infiltration values for the Lincoln soil group were higher than the dense infiltration for the 2017 soils causing the flows to be higher in this area.

• Infiltration rates were similar over the rest of the area, creating almost identical hydrographs to 2007.

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Abbott Before DB07_G&A 17_G&A_D

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Town Before DB07_G&A 17_G&A_D

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SCS v. G&A

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Town Wash

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Green & Ampt vs. SCS 10T

07_G&A SCS 17_G&A_D

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SCS v. G&A

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Town Wash

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Green & Ampt vs. SCS 40T (Town Before DB)

07_G&A SCS 17_G&A_D

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SCS v. G&A

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Abbott Wash

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Green & Ampt vs. SCS 10A

07_G&A SCS 17_G&A_D

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SCS v. G&A

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Abbott Wash

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Green & Ampt vs. SCS Abbott 40A (Before DB)

07_G&A SCS 17_G&A_D

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SCS v. G&A

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Pulsipher Wash

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Green & Ampt vs. SCS 20P (Pulsipher Before DB)

07_G&A SCS 17_G&A_D

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Observations

The more accurate method can only be determined with calibration data

The SCS Curve Number method produced generally lower peak flows than Green & Ampt but runoff volume was generally higher.*

Based on this comparison, it was decided to continue using the Green & Ampt method in Mesquite

*Using G&A Method with Clark UH (per Mohave County Manual) significantly lowered peak flowrates

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Page 25: Green & Ampt or SCS? · The SCS Curve Number method produced generally lower peak flows than Green & Ampt but runoff volume was generally higher.* Based on this comparison, it was

Goal of Model Comparison

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Determine Most Appropriate Method for City of Mesquite

SCSUpdate models to

be more consistent with the rest of Clark County

Green & AmptUpdate models to

use prescribed methodology

(Mohave County)

Page 26: Green & Ampt or SCS? · The SCS Curve Number method produced generally lower peak flows than Green & Ampt but runoff volume was generally higher.* Based on this comparison, it was

G&A with Clark UH

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Town Wash

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Green & Ampt vs. SCS 10T

07_G&A SCS 17_G&A_D 17_MPU

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G&A with Clark UH

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Town Wash

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Green & Ampt vs. SCS 40T (Town Before DB)

07_G&A SCS 17_G&A_D 17_MPU

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G&A with Clark UH

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Abbott Wash

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Green & Ampt vs. SCS 10A

07_G&A SCS 17_G&A_D 17_MPU

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G&A with Clark UH

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Abbott Wash

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Green & Ampt vs. SCS 40A (Abbott Before DB)

07_G&A SCS 17_G&A_D 17_MPU

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G&A with Clark UH

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Pulsipher Wash

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Green & Ampt vs. SCS 20P (Pulsipher Before DB)

07_G&A SCS 17_G&A_D 17_MPU

Page 31: Green & Ampt or SCS? · The SCS Curve Number method produced generally lower peak flows than Green & Ampt but runoff volume was generally higher.* Based on this comparison, it was

Master Plan Impact

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Page 32: Green & Ampt or SCS? · The SCS Curve Number method produced generally lower peak flows than Green & Ampt but runoff volume was generally higher.* Based on this comparison, it was

Master Plan Impacts

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Windmill Wash Detention Basin

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Windmill Wash Detention Basin Inflow

2017 SCS G&A Normal FLO-2D* 2017 G&A

• 522 ac-ft existing• 887 ac-ft expansion proposed

Page 33: Green & Ampt or SCS? · The SCS Curve Number method produced generally lower peak flows than Green & Ampt but runoff volume was generally higher.* Based on this comparison, it was

Thank you

If you’d like to find out more visit:www.atkinsglobal.com© Atkins Limited except where stated otherwise.

The Atkins logo, ‘Carbon Critical Design’ and the strapline‘Plan Design Enable’ are trademarks of Atkins Limited.

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Page 34: Green & Ampt or SCS? · The SCS Curve Number method produced generally lower peak flows than Green & Ampt but runoff volume was generally higher.* Based on this comparison, it was

Supplemental Slides

Basin Specifics

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Page 35: Green & Ampt or SCS? · The SCS Curve Number method produced generally lower peak flows than Green & Ampt but runoff volume was generally higher.* Based on this comparison, it was

Town

The Dense Green and Amptand the SCS methods are overtopping the Detention Basin for Town wash.

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HEC-1Node

2007 MPU

2017 G&A

2017 G&A

Dense

2017 SCS G&A G&A Dense SCS

A W A W A WT1-A 1405 1280 1813 1169 -9% -19% 29% 63% -17% -37%T1-B 1863 1534 2172 1179 -18% -42% 17% 39% -37% -87%1T 3109 2658 3811 2241 -15% 23% -28%T2 2527 1889 2987 1969 -25% -84% 18% 61% -22% -74%T3 977 781 1096 1062 -20% -29% 12% 18% 9% 13%

10T 3943 2924 4779 3651 -26% 21% -7%T4 926 710 912 777 -23% -15% -2% -1% -16% -10%T5 2556 1490 2154 2134 -42% -139% -16% -53% -17% -55%

20T 3915 2266 4320 4188 -42% 10% 7%T6 2503 1793 2446 2314 -28% -99% -2% -8% -8% -26%

30T 4219 2363 4556 4876 -44% 8% 16%T7 1215 1167 1190 901 -4% -4% -2% -2% -26% -28%T8 946 850 924 742 -10% -10% -2% -2% -22% -21%

40T 4543 2685 4889 5426 -41% 8% 19%TWDB 602 496 1232 3300 -18% 105% 448%T9-A 775 747 762 618 -4% -2% -2% -1% -20% -11%51T 775 747 762 618 -4% -2% -20%T9-C 700 672 684 618 -4% -2% -2% -1% -12% -5%52T 1445 1389 1417 1202 -4% -2% -17%T9-B 1611 1537 1575 1367 -5% -5% -2% -2% -15% -16%

60T (I-15) 2870 2738 2804 2390 -5% -2% -17%T10 604 612 620 453 1% 1% 3% 1% -25% -12%

70T (Virgin River) 3394 3273 3344 2764 -4% -1% -19%T10A 246 260 261 187 6% 1% 6% 1% -24% -4%T11 104 124 128 69 19% 1% 23% 2% -34% -2%

Combined Differences -15% -21% 10% 5% 4% -17%

100-Year Flows for Town Wash

Page 36: Green & Ampt or SCS? · The SCS Curve Number method produced generally lower peak flows than Green & Ampt but runoff volume was generally higher.* Based on this comparison, it was

Abbott

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HEC-1 Node

2007 MPU

2017 G&A

2017 G&A

Dense

2017 SCS

G&A G&A Dense SCS

A W A W A WA1 1217 874 1217 1139 -28% -32% 0% 0% -6% -7%A2 744 517 726 1025 -31% -24% -2% -2% 38% 30%

10A 1566 1055 1547 1494 -33% -1% -5%A3 511 367 501 450 -28% -16% -2% -1% -12% -7%A4 287 220 285 257 -23% -7% -1% 0% -10% -3%

20A 1894 1259 1863 1851 -34% -2% -2%A5 730 722 742 566 -1% -1% 2% 1% -22% -11%

40A5 2033 1401 2008 1983 -31% -1% -2%A6 702 510 686 604 -27% -18% -2% -2% -14% -9%A7 367 278 358 298 -24% -7% -2% -1% -19% -5%

30A 1037 699 1012 881 -33% -2% -15%A8 413 422 428 329 2% 1% 4% 2% -20% -10%

40A 3082 2281 3081 2878 -26% 0% -7%AWDB 334 281 334 658 -16% 0% 97%A9-C 992 994 1019 831 0% 0% 3% 2% -16% -12%41A 992 994 1019 831 0% 3% -16%A9-B 942 887 896 612 -6% -5% -5% -4% -35% -29%

50A (I-15) 1820 1769 1802 1340 -3% -1% -26%A10 548 598 602 455 9% 5% 10% 5% -17% -9%

60A (Virgin River) 2206 2203 2240 1671 0% 2% -24%

Combined Difference -17% -15% 0% 0% -7% -11%

100-Year Flows for Abbott Wash

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Pulsipher

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HEC-1Node

2007 MPU

2017 G&A

2017 G&A

Dense

2017 SCS G&A G&A Dense SCS

A W A W A WP1 944 845 935 745 -10% -9% -1% -1% -21% -18%P2 760 761 770 705 0% 0% 1% 1% -7% -4%10P 1333 1249 1333 1045 -6% 0% -22%P3 1061 1132 1164 951 7% 6% 10% 9% -10% -9%20P 1968 1978 2073 1652 1% 5% -16%

PWDB 148 285 464 209 93% 214% 41%P4 900 914 946 745 2% 1% 5% 4% -17% -14%30P 909 844 875 680 -7% -4% -25%P6 509 365 503 508 -28% -21% -1% -1% 0% 0%P7 622 585 629 532 -6% -4% 1% 1% -14% -9%

40P 1808 1576 1763 1510 -13% -2% -16%P8 479 458 468 413 -4% -1% -2% -1% -14% -4%

50P (I-15) 2105 1871 2058 1753 -11% -2% -17%P9 166 155 163 88 -7% -1% -2% 0% -47% -6%

60P (Virgin River) 2218 1987 2173 1815 -10% -2% -18%

Combined Difference 0% -6% 15% 2% -14% -13%

100-Year Flows for Pulsipher Wash

Page 38: Green & Ampt or SCS? · The SCS Curve Number method produced generally lower peak flows than Green & Ampt but runoff volume was generally higher.* Based on this comparison, it was

Additional

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HEC-1Node

2007 MPU

2017 G&A

2017 G&A

Dense

2017 SCS G&A G&A Dense SCS

A W A W A WAD-1 493 552 559 293 12% 4% 13% 4% -41% -13%A9a 176 170 172 149 -3% 0% -2% 0% -15% -1%AD-2 603 689 691 506 14% 8% 15% 8% -16% -9%10AD 741 821 825 618 11% 11% -17%AD-3 190 205 206 152 8% 1% 8% 1% -20% -3%AD-4 615 730 733 513 19% 11% 19% 12% -17% -10%AD-5 379 437 446 214 15% 6% 18% 7% -44% -17%

Combined Differences 11% 14% 12% 15% -24% -25%

100-Year Flows for Additional Washes

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Western & Unnamed

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HEC-1Node

2007 MPU

2017 G&A

2017 G&A

Dense

2017 SCS G&A G&A Dense SCS

A W A W A WW1 1040 1046 1110 971 1% 1% 7% 8% -7% -8%W2 147 146 148 125 -1% 0% 1% 0% -15% -1%W3 564 525 542 405 -7% -3% -4% -2% -28% -11%W4 240 240 243 224 0% 0% 1% 0% -7% -1%W5 306 316 319 293 3% 1% 4% 1% -4% -1%

W6a 808 545 858 1063 -33% -46% 6% 9% 32% 45%W6b 1136 778 1091 1012 -32% -62% -4% -8% -11% -22%10W 1805 1208 1810 1947 -33% 0% 8%

Combined Difference -13% -21% 1% 2% -4% 0%

100-Year Flows for Western Wash

100-Year Flows for Unnamed Wash

HEC-1Node

2007 MPU

2017 G&A

2017 G&A

Dense

2017 SCS

G&AG&A Dense SCS

U1 (I-15) 740 733 733 581 -1% -1% -21%