Hydrologic Analysis Techniques (‘87 Manual “Hydrology Tools”)€¦ · Know which wetland applies to which technique Define the Wetland Water Budget Locate data Understand the

Hydrologic Analysis Techniques (‘87 Manual “Hydrology Tools”)

Objectives

Know which wetland applies to which technique

Define the Wetland Water Budget

Locate data

Understand the “time step”

Understand Limitations

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Objective Criteria

Farmed Wetland (FW) •Inundated for 15 Continuous Days •In most years (50% chance or more) •During Growing Season

•USACE Groundwater Monitoring for Wetland (W) •Saturated Within 12” of surface •50% Annual Probability •During Growing Season •15 Continuous Days

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•50% chance can be: •Median

•Middle number in a population •2-yr Log-Pearson

•Commonly used for return period of annual peak discharges

•50th Percentile •Calculated from a “Weibull Plot”

Probabilities (What does “in a normal year” mean?)

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Probability/Duration Analysis

Analysis can be performed on: •Stream gage records •Groundwater levels •Lake Stages •Ponded Storage •Example Results: •50% Chance annual probability of 7 days of continuous inundation •80% Chance annual probability of 20 days of saturation within 6” of the surface •80% Chance probability of inundation to depth of 3’

I – O = ΔS (Inflow – Outflow = Change in Storage) Inflows and Outflows: P = Precipitation Ri = Surface Runoff in Ro = Surface Runoff out Gi = Groundwater discharge in Go = Groundwater recharge out ET = Evapotranspiration

“Simplified” Water Budgeting

The Time Step

Monthly • Simplified Water Budgeting Daily • Most hydrology modeling techniques,

including SPAW Model Sub-Hourly • DRAINMOD – Converts Daily Precipitation

to sub-hourly distribution

Wetland Storage

Surface Storage • Topographic Storage using Stage-Storage

Curve • Depth of Storage – if topography is

relatively flat and area of inundation changes little with increasing depth in the

• “Surface Roughness” Storage Soil Storage • Use Available Water Capacity in Simplified

Method

Applicable Wetland Type – “Simplified” • Limited to Recharge DEPRESSION HGM Class • Monthly Time Step • Soil Storage Loss stops when moisture is at

Permanent Wilting Point • Soil is “full” at saturation (higher than field

capacity) • Ro occurs when topographic storage depth is

exceeded • Depression area varies little with depth, volume

is expressed as depth • All other water budget parameters expressed as

depth • Gi neglected, Go stops when profile is saturated

Monthly Precipitation, P

WETS Table Tables

Soil Storage

0 to 5 inches – 0.23 in/in 5 to 32 inches – 0.16 in/in Assume root depth (24”?) (5 x 0.23) + (19 x 0.16) = 4.19”

Monthly Evapotranspiration NOAA Atlas 34 – Data for Scottsbluff, NE

January – 1.51 February – 1.89 March – 3.14 April – 5.10 May – 6.95 June – 8.46 July – 9.77 August – 8.60 September – 6.04 October – 4.32 November – 2.38 December – 1.59

Animal Waste Management (AWM) Software has monthly evaporation files

Surface Runoff

• Runoff Curve Number Method • Curve Numbers Meant for use with daily

rainfall • Must convert RCN to CN30 for use with monthly

rainfall • This method used by the AWM program for

feedlot runoff • The CN30 is the “30 day Curve Number”

CN30 = CN1 – (CN1 – ((CN1^2.365)/631.79) - 15) log 30

CN of 85 = CN30 of 67

Example: Use: • WETS Monthly Rainfall • Monthly Evaporation Data

Given • Soil Storage of 4.19”

Assume: • Overflow Depth of 1 feet • Watershed to Depression

Ration of 20:1 • CN30 = 67

Solution:

SPAW -- A DAILY HYDROLOGIC MODEL

FOR FIELDS AND PONDS

A Numerical Model for Recharge Depressions

K. E. Saxton USDA/ARS Pullman, WA

Patrick Willey USDA/NRCS Portland, OR

SPAW MODEL Applications

Daily hydrologic budgets of agricultural fields, ponds, and wetlands.

Realistic and accurate water budgets with general site descriptions, data and parameters.

Long-term simulations and analyses with reasonable computer time.

MODEL CONFIGURATION

SPAW: Soil-Plant-Air-Water model providing daily vertical water budget of agricultural fields.

POND: Model providing daily inundated pond water budget.

FIELD: Model providing daily soil moisture balance, runoff and recharge

Pond budget linked to field(s) hydrology -- precipitation, runoff, interflow, evaporation

MAIN SCREEN •File •Edit •Options •Data •Projects

•Field/Pond •View •Window •Help/Tutorial

Agricultural Field Hydrology

SPAW FIELD ANALYSES

Daily water budgets of dryland and irrigated fields.

Crop water stress, irrigation water requirements and schedules.

Runoff, percolation, soil water profiles Nitrogen budgets

FIELD Data Inputs

•Climate: Precip., evap., temp. •Crop: Canopy, greeness, roots •Soil: depths, textures •Management:

•crop rotations, irrigation

Graphical Output

•Select Variable: •Daily Precip. •Accum. Precip. •Daily runoff •Accum. runoff

Wetland / Pond / Reservoir

SPAW-POND Analyses •Daily ponded water budgets—inflows, storage, evaporation, seepage, outflows. •Wetland frequency and duration of inundation. •Lagoon design and operations. •Water supply design for livestock or irrigation.

POND Description

•Field(s) hydrology •Depth-Area relationship •Infiltration, seepage •Depths: outlets, spillways, pumps inlets •Watertable depths •Pumping rates & times

POND Graphical Output

Select Variable: •Daily Precip. •Pond Depth •Accum. Evap. •Accum. seepage

DEPTH (FT): DRY 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00

AREA (AC): 1.00 1.25 1.50 1.75 2.00 2.63 3.25 3.88 4.50 5.25 6.00

YEARS (%) : 84% 84% 74% 61% 52% 52% 45% 29% 19% 6% 0%

PERCENTAGE OF YEARS POND DEPTH GREATER THAN GIVEN DEPTHS(10% INTERVALS)FOR 14 CONSECUTIVE DAYS DURING THE WETLAND GROWING SEASON: Apr 1 TO Sep 30

Wetland Statistical Analyses

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Stream Gage Data Analysis

Temporary Flooding

Long Term Ponding

Riverine HGM Class Wetland Sites

Training Session Objective

To demonstrate how gage data can be used in the wetland determination process

To show how gage data information can be useful in hydrology restoration planning

To Show how other data can be statistically analyzed

To Introduce the HEC-EFM Software

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• Daily Mean Flow Data is the Default

• Daily Peak and Minimum Data Sometimes Available

• Daily Stage Sometimes Available

Will flood inundation analysis work in your Area?

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Will it work in your Area?

Duration?

Typical Peak

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Will it work in your Area? Web Soil Survey Flooding •Duration

•Brief – 2 to < 7 days •Frequency

•Frequent - >50 times in 100 years

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Western Snowmelt Hydrographs

Long Durations – But low peaks

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Other Parameters - Peak Discharges

Instantaneous Peak Discharges (50% Chance Annual Probability)

Fill Floodplain Depressions (Duration from Water Budgeting)

Data Requirements for Floodplain Inundation Analysis

Continuous Flow Values for 10 years (minimum) up to 30 years

Topographic Information for potential wetland site

Cross Section of Stream Channel or Channel Rating Information

Water Surface Profile Information if Site is not adjacent to gage

Sources of Data

USGS-NWIS

COE, TVA, BOR, NOAA

State Water Resource Agencies

Data usually includes Daily Mean Flow

May Include Stage, Peak Flows, Minimum Flows, Flow Statistics

USGS Qualitative Adjectives Assigned to Mean Daily Discharges

Excellent - 95% of Daily Discharge Within 5% of Rating Curve

Good - 95% of Daily Discharge Within 10% of Rating Curve

Fair - 95% of Daily Discharge Within 15% of Rating Curve

Poor - Daily Discharges Have Less than Fair Accuracy

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Data Requirements Flow Data

Mean Daily Flow File Gage Datum

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Order: Text File, Tab-delimited Can open in Spreadsheet

Flow

Date

Data Requirements Flow Data

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Data Requirements Channel Rating

Gage Height

Flow

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NRCS Guidance on Rating Curves

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Site Topography USGS Quad Maps

James River @ Huron, South Dakota 15-day, 50% chance Flow obviously Exceeds 10 ft. floodplain contour

Site

Gage Station

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Water Surface Profiles – HEC-GeoRAS Product

Procedures:

• Determine the Growing Season

• Determine the Appropriate Duration of Inundation

• Locate the Closest Stream or Lake Gage

• Obtain Mean Daily Flow Values for Growing Season

• Determine Lowest Flow/Stage for Each Duration

Procedures Continued:

• Determine the Highest of the Annual Low Duration Flows for Each Year

• Tabulate Flow/Stage in Descending Order

• Determine the Median Value of Flow/Stage

• Associate Median Value With Elevation

Procedures Continued

• If 50% Chance is Discharge, Relate it to Elevation

• If Available, Use Computerized Stream Flow Data

• Determine Area Inundated Critical Duration

Day Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep1 87 427 459 797 1380 674 1210 12100 303 483 297 2582 94 367 506 819 1200 723 1050 10200 304 365 275 4673 99 267 508 772 1120 1060 874 4120 365 281 213 5504 93 299 508 657 1050 1460 810 1590 421 257 365 4815 93 359 495 556 978 1640 729 2020 377 241 490 3376 64 1610 526 622 936 1680 710 2890 326 144 543 2437 50 5360 564 868 898 1390 670 3830 307 210 807 2048 85 7490 881 921 860 1200 588 4400 394 165 1190 1719 103 6970 687 1190 802 1190 588 3770 791 131 780 126

10 71 5490 508 1660 815 2920 539 2950 941 179 754 14111 80 2260 448 2670 802 4850 550 3430 826 208 738 16012 108 977 412 3520 749 6120 561 3620 624 223 547 18713 121 706 366 3020 727 6400 533 2180 426 380 451 21914 153 572 413 2810 764 6330 555 1500 317 370 598 19015 141 494 754 3760 786 5630 544 1900 306 275 892 19316 87 452 1090 4400 783 2200 513 2450 259 1170 1320 15117 117 426 1610 4490 819 1550 470 1830 195 2230 709 12818 125 396 1220 3230 833 1330 553 1340 246 3400 404 15719 94 404 1230 3040 870 1150 1030 1040 264 3340 222 13120 106 331 1410 6040 839 1020 1630 863 153 1130 207 5621 104 330 1460 7260 773 1000 1370 723 263 604 195 12622 158 320 1670 7300 756 940 1080 624 125 441 204 8324 391 333 2130 5870 721 820 646 541 394 281 165 14325 886 349 1270 3180 739 760 515 440 341 790 162 51926 666 409 1030 2620 711 1100 2210 455 307 1250 160 45727 177 409 1010 3510 675 2200 6170 432 510 1750 138 20728 943 411 897 4420 622 3120 8650 416 1360 1270 222 21629 2400 407 739 5110 3550 9440 417 1630 650 171 20130 1150 349 660 5560 2450 11100 249 937 445 133 10631 623 744 2980 1520 308 382 157

674


10 71 5490 508 1660 815 2920 539 2950 941 179 754 14111 80 2260 448 2670 802 4850 550 3430 826 208 738 16012 108 977 412 3520 749 6120 561 3620 624 223 547 18713 121 706 366 3020 727 6400 533 2180 426 380 451 21914 153 572 413 2810 764 6330 555 1500 317 370 598 19015 141 494 754 3760 786 5630 544 1900 306 275 892 19316 87 452 1090 4400 783 2200 513 2450 259 1170 1320 15117 117 426 1610 4490 819 1550 470 1830 195 2230 709 12818 125 396 1220 3230 833 1330 553 1340 246 3400 404 15719 94 404 1230 3040 870 1150 1030 1040 264 3340 222 13120 106 331 1410 6040 839 1020 1630 863 153 1130 207 5621 104 330 1460 7260 773 1000 1370 723 263 604 195 12622 158 320 1670 7300 756 940 1080 624 125 441 204 8324 391 333 2130 5870 721 820 646 541 394 281 165 14325 886 349 1270 3180 739 760 515 440 341 790 162 51926 666 409 1030 2620 711 1100 2210 455 307 1250 160 45727 177 409 1010 3510 675 2200 6170 432 510 1750 138 20728 943 411 897 4420 622 3120 8650 416 1360 1270 222 21629 2400 407 739 5110 3550 9440 417 1630 650 171 20130 1150 349 660 5560 2450 11100 249 937 445 133 10631 623 744 2980 1520 308 382 157

674

723


10 71 5490 508 1660 815 2920 539 2950 941 179 754 14111 80 2260 448 2670 802 4850 550 3430 826 208 738 16012 108 977 412 3520 749 6120 561 3620 624 223 547 18713 121 706 366 3020 727 6400 533 2180 426 380 451 21914 153 572 413 2810 764 6330 555 1500 317 370 598 19015 141 494 754 3760 786 5630 544 1900 306 275 892 19316 87 452 1090 4400 783 2200 513 2450 259 1170 1320 15117 117 426 1610 4490 819 1550 470 1830 195 2230 709 12818 125 396 1220 3230 833 1330 553 1340 246 3400 404 15719 94 404 1230 3040 870 1150 1030 1040 264 3340 222 13120 106 331 1410 6040 839 1020 1630 863 153 1130 207 5621 104 330 1460 7260 773 1000 1370 723 263 604 195 12622 158 320 1670 7300 756 940 1080 624 125 441 204 8324 391 333 2130 5870 721 820 646 541 394 281 165 14325 886 349 1270 3180 739 760 515 440 341 790 162 51926 666 409 1030 2620 711 1100 2210 455 307 1250 160 45727 177 409 1010 3510 675 2200 6170 432 510 1750 138 20728 943 411 897 4420 622 3120 8650 416 1360 1270 222 21629 2400 407 739 5110 3550 9440 417 1630 650 171 20130 1150 349 660 5560 2450 11100 249 937 445 133 10631 623 744 2980 1520 308 382 157

674

723

1060


10 71 5490 508 1660 815 2920 539 2950 941 179 754 14111 80 2260 448 2670 802 4850 550 3430 826 208 738 16012 108 977 412 3520 749 6120 561 3620 624 223 547 18713 121 706 366 3020 727 6400 533 2180 426 380 451 21914 153 572 413 2810 764 6330 555 1500 317 370 598 19015 141 494 754 3760 786 5630 544 1900 306 275 892 19316 87 452 1090 4400 783 2200 513 2450 259 1170 1320 15117 117 426 1610 4490 819 1550 470 1830 195 2230 709 12818 125 396 1220 3230 833 1330 553 1340 246 3400 404 15719 94 404 1230 3040 870 1150 1030 1040 264 3340 222 13120 106 331 1410 6040 839 1020 1630 863 153 1130 207 5621 104 330 1460 7260 773 1000 1370 723 263 604 195 12622 158 320 1670 7300 756 940 1080 624 125 441 204 8324 391 333 2130 5870 721 820 646 541 394 281 165 14325 886 349 1270 3180 739 760 515 440 341 790 162 51926 666 409 1030 2620 711 1100 2210 455 307 1250 160 45727 177 409 1010 3510 675 2200 6170 432 510 1750 138 20728 943 411 897 4420 622 3120 8650 416 1360 1270 222 21629 2400 407 739 5110 3550 9440 417 1630 650 171 20130 1150 349 660 5560 2450 11100 249 937 445 133 10631 623 744 2980 1520 308 382 157

674

723

1060

1190


10 71 5490 508 1660 815 2920 539 2950 941 179 754 14111 80 2260 448 2670 802 4850 550 3430 826 208 738 16012 108 977 412 3520 749 6120 561 3620 624 223 547 18713 121 706 366 3020 727 6400 533 2180 426 380 451 21914 153 572 413 2810 764 6330 555 1500 317 370 598 19015 141 494 754 3760 786 5630 544 1900 306 275 892 19316 87 452 1090 4400 783 2200 513 2450 259 1170 1320 15117 117 426 1610 4490 819 1550 470 1830 195 2230 709 12818 125 396 1220 3230 833 1330 553 1340 246 3400 404 15719 94 404 1230 3040 870 1150 1030 1040 264 3340 222 13120 106 331 1410 6040 839 1020 1630 863 153 1130 207 5621 104 330 1460 7260 773 1000 1370 723 263 604 195 12622 158 320 1670 7300 756 940 1080 624 125 441 204 8324 391 333 2130 5870 721 820 646 541 394 281 165 14325 886 349 1270 3180 739 760 515 440 341 790 162 51926 666 409 1030 2620 711 1100 2210 455 307 1250 160 45727 177 409 1010 3510 675 2200 6170 432 510 1750 138 20728 943 411 897 4420 622 3120 8650 416 1360 1270 222 21629 2400 407 739 5110 3550 9440 417 1630 650 171 20130 1150 349 660 5560 2450 11100 249 937 445 133 10631 623 744 2980 1520 308 382 157

674

723

1060

1190


10 71 5490 508 1660 815 2920 539 2950 941 179 754 14111 80 2260 448 2670 802 4850 550 3430 826 208 738 16012 108 977 412 3520 749 6120 561 3620 624 223 547 18713 121 706 366 3020 727 6400 533 2180 426 380 451 21914 153 572 413 2810 764 6330 555 1500 317 370 598 19015 141 494 754 3760 786 5630 544 1900 306 275 892 19316 87 452 1090 4400 783 2200 513 2450 259 1170 1320 15117 117 426 1610 4490 819 1550 470 1830 195 2230 709 12818 125 396 1220 3230 833 1330 553 1340 246 3400 404 15719 94 404 1230 3040 870 1150 1030 1040 264 3340 222 13120 106 331 1410 6040 839 1020 1630 863 153 1130 207 5621 104 330 1460 7260 773 1000 1370 723 263 604 195 12622 158 320 1670 7300 756 940 1080 624 125 441 204 8324 391 333 2130 5870 721 820 646 541 394 281 165 14325 886 349 1270 3180 739 760 515 440 341 790 162 51926 666 409 1030 2620 711 1100 2210 455 307 1250 160 45727 177 409 1010 3510 675 2200 6170 432 510 1750 138 20728 943 411 897 4420 622 3120 8650 416 1360 1270 222 21629 2400 407 739 5110 3550 9440 417 1630 650 171 20130 1150 349 660 5560 2450 11100 249 937 445 133 10631 623 744 2980 1520 308 382 157

674

723

1060

1190

1590

Year Discharge 1981 0 1982 973 1983 545 1984 1360 1985 137 1986 3750 1987 1280 1988 33 1989 1100 1990 79

Rank Discharges

Year Discharge Ranked 1981 0 3750 1982 973 1360 1983 545 1280 1984 1360 1100 1985 137 973 1986 3750 545 1987 1280 137 1988 33 79 1989 1100 33 1990 79 0

Year Discharge Ranked 1981 0 3750 1982 973 1360 1983 545 1280 1984 1360 1100 1985 137 973 1986 3750 545 1987 1280 137 1988 33 79 1989 1100 33 1990 79 0

Year Discharge Ranked 1981 0 3750 1982 973 1360 1983 545 1280 1984 1360 1100 1985 137 973 1986 3750 545 1987 1280 137 1988 33 79 1989 1100 33 1990 79 0 Median Value = (973+545)/2 = 759 cfs

1. Determine elevation from rating curve

2. Draw Contour on Map

3. What is your answer?

Exercise

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HEC – Ecosystem Functions Model (EFM)

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Observation Wells

Objectives Upon completion of the training you will be able to: - Describe the parts of an observation well and the

materials used to install them - Install observation wells to document duration and

frequency of saturation - List and explain uses of observation wells and

piezometers - Gather and interpret monitoring well data needed

to obtain statistically significant results - List general guidelines for reviewing well

selection, installation and data collection procedures, and data analysis

Observation Wells Monitoring a Shallow Water Table

• Correct instrumentation

(observation well or piezometer)

• Correct installation

• Correct data collection, daily readings during growing season critical time

• Correct interpretation of data

Site Evaluation

• Start with a good soil profile description

• Respect all impermeable layers

• Plug any holes into or through with impermeable material

Water Table

The upper surface of the zone of saturation is called the water table. The hydraulic pressure at any level within a water-table aquifer is equal to the depth from the water table to the point in question and may be expressed as hydraulic head in feet of water.

Typical application of observation wells, Scope and Effect equations, DRAINMOD Endosaturation: The soil is saturated with water in all layers from the upper boundary of saturation to a depth of 200 cm or more from the mineral soil surface.

>=200 cm

ENDOSATURATION

<200cm

Top of unsaturated zone

<200cm

- Episaturation: The soil is saturated with water in one or more layers within 200 cm of the mineral soil surface and also has one or more unsaturated layers, with an upper boundary above a depth of 200 cm, below the saturated layer. - The zone of saturation , i.e., the water table, is perched on top of a relatively impermeable layer.

EPISATURATION

• Care must be taken in applying Scope and Effect equations, DRAINMOD to this situation.

• Which water table is being analyzed? • How do you install observation wells and interpret data?

• Well Points no longer recommended, leave bottom open. • 15” max. length now recommended for wells in wetlands.

Impermeable layer

• Piezometers typically installed in confined aquifers for g.w. flow.

• Monitoring wells do not penetrate a confining layer.

• Piezometers by definition have perforated interval installed below a confining layer. No confining layer, no piezometer.

• Always need a good soil profile description.

• Monitoring well penetrates a confining layer. Erroneous readings will result.

• Piezometer’s perforated interval installed below a confining layer. Correct reading on piezometric head in lower layer. Artesian condition in piezometer. Does not read perched water table.

Ground water flow

Perched

Artesian, confined aquifer

• Monitoring wells used in water table aquifers. Open to atmosphere.

• Piezometers are installed in confined aquifers. Artesian if water level rises above confining layer, flowing artesian if water comes to soil surface. Water flows from higher to lower piezometric head.

Correct Incorrect

Identifying a Perched WT Using Piezometers (after Sprecher, 1993)

1. Cap too tight (use 3”on 2” pipe)

2. Displacement of water in well by measuring device misrepresents true water level (2” dowel rod in 3” pipe)

3. Infrequent readings (readings on day 1 and 14 doesn’t describe what happens in between, continuous duration)

4. 1 year of data (cannot establish frequency, 50% of years)

5. No soil profile description (what the heck is being monitored)

Problems Often Encountered with Observation Wells:

6. No replication (one well only, can’t detect problems)

7. Well screen plugged (no water movement)

8. Frost heaving (re-install well)

9. Cracking soil (macropore flow)

10. No on-site raingage (well/rainfall interaction, moving infiltration)

Problems Often Encountered with Observation Wells (cont.)

Figure 4.14 Hypothetical example in which soil is continuously saturated in the root zone during

A. Normal and

B. Above normal precipitation conditions.

• In the case of A., the area may qualify as a jurisdictional wetland.

• In the case of B., more conclusive evidence would be needed to determine that the area is a jurisdictional wetland.

Observation Well Data

• Minimum 10 years required if used alone

• Minimum of 5 years if used with WETS table normalization procedure

• Less than 5 years can be used with extreme caution, using normalization procedure if precipitation is below normal and water table exists to meet criteria

• One year of data should be compared to DRAINMOD analysis of site using Reference Wetland Simulation procedure

Observation Wells

• Must have soil profile description of each well site

• Install wells in pairs to confirm readings are correct

• Local rainfall gage needed - on-site if possible - recording tipping bucket rain gage ideal

• Note date of leaf out in spring if wooded site, senescence in fall (ET can drop water table significantly)

Drainage Equations

Chapter Objectives

Introduce the 4 Drainage Equations Explain the conditions for use of each List and describe the inputs for each Prepare for an Ellipse Equation Exercise

Drainage Equations Apply Directly to MINERAL FLAT Wetlands

• All water budget vectors are vertical before drainage • Drainage introduces horizontal flow

Effects of Drainage Systems

Estimate the lateral effect of a ditch or subsurface drain on the water table

Typical application of observation wells, drainage equations, DRAINMOD

ENDOSATURATION

Drainage Equations

Ellipse

Hooghoudt (used in DRAINMOD)

van Schilfgaarde

Kirkham - removal of surface water (used in DRAINMOD)

Figure 1: Example Using The Ellipse Equation

S = [(4K) (m2 + 2am) / q]1/2

m=d-c

Ellipse Equation

S = [(4K) (m2 + 2am) / q]1/2

K and q must be in same units, e.g. in/hr, ft/day

S will be in units of a and m

Le = S / 2

m=d-c

How do we get Lateral Effect out of this?

Hydraulic Conductivity

Where K and T Are the Saturated Hydraulic Conductivity and Thickness of Each Layer

(flow being evaluated is horizontal flow only, so flow is by layers)

Turns isotropic layers to anisotrophic profile

K1 T1

K2 T2

K3 T3

DrainageFeature

K1 T1

K2 T2

K3 T3

DrainageFeature

K1 T1

K2 T2

K3 T3

Soil A Soil BChoose more

restrictive: Soil A or B

Example Problem

K = 1.3 in/hr

K = 0.9 in/hr

K = 0.15 in/hr

12 in

48 in

52 in

What hydraulic conductivity do we

use?

Answer

K = 0.98 in/hr

K = 1.3 in/hr * 12 in + 0.9 in/hr * 48 in 60 in

Ellipse Equation

S = [(4K) (m2 + 2am) / q]1/2

q =

q is the drainage rate How much water needs to

be removed by when?

For wetland hydrology determination, q is evaluated as water that must be removed by drainage in lowering water table (drained volume) divided by the time to remove.

Example: lower water table from surface to 12” in 14 days.

Drained volume is 0.01” (WT 0” to -12”)

q = 0.01 in/14 days = .00071 in/day

Water Table Depth of water DrainableDepth Drained Porosity 0 - Depth

(cm) (cm) (cm/cm).0000 .0000 N/A10.0000 .0582 0.0058220.0000 .1819 0.0091030.0000 .4054 0.0135140.0000 .7358 0.0184050.0000 1.1632 0.0232660.0000 1.6767 0.02795

Table 1. Drainable Porosity for Commerce Soil

Values shown for Water Table Depth and Depth of Water drained have already integrated data for multiple soil layers into one “soil”

Drainable Porosity is a function of drawdown, NOT a soil property

Calculation of Drainable Porosity

The drainable porosity if the water table is lowered from Depth 1 to Depth 2 is:

(Drained Volume Depth 1 — Drained Volume Depth 2)

Drainable Porosity Depth 1 - Depth 2 = ------------------------------------------------------------------

(Depth 1 — Depth 2)

Water Table Depth of water DrainableDepth Drained Porosity 0 - Depth

(cm) (cm) (cm/cm).0000 .0000 N/A10.0000 .0582 0.0058220.0000 .1819 0.0091030.0000 .4054 0.0135140.0000 .7358 0.0184050.0000 1.1632 0.0232660.0000 1.6767 0.02795

Example: Calculate Drainable porosity to 30 cm

Example 1. The drainable porosity if the water table is lowered from 0 cm to 30 cm is

Drainable Porosity 0-30

f = (0.0 cm -.4054 cm)/(0 cm-30 cm)

= (-0.4054 cm)/(-30 cm) = 0.0135 cm/cm

Example 2. The drainable porosity if the water table is lowered from 10 cm to 30 cm is: Drainable Porosity10-30 = (0.0582 cm - .4054 cm)/(10 cm-30 cm) = (-0.3472 cm) / (-20 cm) = 0.01736 cm / cm

Drainable Porosity Use in Scope and Effect Equations • Drainable porosity (f) is used directly in the van

Schilfgaarde equation.

• In the Ellipse and Hooghoudt equations it is used as follows to calculate a drainage rate q.

(f *depth water table lowered) + rainfall -evapotranspiration q = t t = time to lower water table for most critical period during the growing season

Where do you get the Soil data?

1.Field Data - Collect soil samples and perform laboratory analysis.

Or,

2. NRCS National Soil Information System (NASIS database)

• % Sand, Silt, and Clay • Water capacity @ 33 kPa and 1500 kPa • Moist Bulk density • Depth to top and bottom of each layer

Rosetta Model (ARS, Riverside, CA)

Rosetta uses Pedotransfer functions and the information from the NASIS database to predict: • water retention • Hydraulic conductivity

Texture Drained f Ksat Class Vol@30 cm 0-30 cm (cm) (cm/cm) (cm/hr) Clay 0.317 0.0106 0.615 C Loam 0.413 0.0138 0.341 Loam 0.248 0.0083 0.502 L Sand 1.231 0.0410 4.383 Sand 1.318 0.0439 26.779 S Clay 0.470 0.0157 0.473 S C L 0.470 0.0157 0.549 S Loam 0.761 0.0254 1.595 Silt 0.131 0.0044 1.823 Si Clay 0.397 0.0132 0.401 Si C L 0.192 0.0064 0.463 Si Loam 0.074 0.0025 0.760

Values from ROSETTA Class Averages

qmKamKS /48(' 212 +=

• K1 = weighted hydraulic conductivity above the drainage feature, in/hr

• K2= weighted hydraulic conductivity below the drainage feature, in/hr Note: K1 and K2 do not have to be different

• (also uses an equivalent depth that will be discussed later)

Hooghoudt Equation

NRCS Modified van Schilfgaarde Equation NRCS uses a modified version of the van Schilfgaarde

equation in which the drainable porosity is replaced with an adjusted drainable porosity, which accounts for the water storage (s) by surface roughness. If surface roughness is ignored (s=0), the equation is identical to the original van Schilfgaarde equation.

van Schilfgaarde Equation

S = drain spacing m = height of water table above the center of the drain at midplane

after time t, ft m0 = initial height of water table above the center of the drain at t =

0, ft t = time for water table to drop from m0 to m, days a = depth from free water surface in drainage feature to

impermeable layer, ft f’ = modified drainable porosity de = equivalent depth

f’ – modified drainable porosity

f’ = f + (s/(mo – m) s = water trapped on the surface by

soil roughness, ft s = 0.0083 ft (0.1 in) would be typical

Note: set s = 0 if unsure of appropriate

value

Surface Ponding (Microtopography)

Average depth of storage that occurs before runoff begins.

Distributed across the field - average

Surface Storage is often the most critical factor – will make or break a determination

Surface Storage Depths

Surface Storage

Description

Well graded cropland

0.1 to 0.5 cm Surface relatively smooth and on grade so that water does not remain ponded in field after heavy rainfall. No potholes and adequate outlets.

Fair cropland

1.0 to 1.5 cm Some shallow depressions, water remains in a few shallow pools after heavy rainfall. Microstorage caused by disking or cultivation may cause surface drainage to be only fair even when field surface is on grade.

Pasture 1.5 to 2.5 cm Many depressions or potholes of varying depth. Widespread ponding of water after heavy rainfall. Or inadequate surface outlets such as berms around field ditches.

Improved Forest

1.5 to 3.0 cm Depressions of varying depth.

Native Forest

2.5 to 5.0 cm Many depressions of varying depth. Widespread ponding that can last for days.

Natural Microtopography

Ponding

Kirkham’s Equation

Kirkham’s Equation for Parallel Drains

For removal of ponding only

Figure 2: Pothole With Tile Drainage System

Kirkham’s Equation

Organic Soils • Difficult to determine Ksat and f • Most organic soils are on discharge

wetlands • Lateral groundwater flow in • Does not match vertical hydrodynamics

of Mineral Flats

Drainmod

Explain major DRAINMOD features List major DRAINMOD inputs List major DRAINMOD outputs Interpret basic wetland hydrology

output Select the HGM class applicable to

DRAINMOD

DRAINMOD Program Features

DRAINMOD was developed by Dr. R. Wayne Skaggs at North Carolina State University (1980)

• DRAINMOD is a computer model (program) that is used to simulate the hydrology of high water table soils on an hourly basis for long periods of record (typically > 20 years)

Graphical Output Mineral Flat – Willamette Valley, OR – “Wet Prairie”

HGM Class Applicable to DRAINMOD

The DRAINMOD model is applicable to wetlands in the MINERAL FLATS wetland class. DRAINMOD accurately models removal

of water from shallow depressions within MINERAL FLAT wetlands

DRAINMOD is not appropriate for modeling deep depressions within the DEPRESSION HGM class

Questions?

Documents

Hydrologic Analysis Techniques (‘87 Manual “Hydrology Tools”)€¦ · Know which wetland applies to which technique Define the Wetland Water Budget Locate data Understand the