Hydrologic Analysis Techniques ( 87 Manual Hydrology Tools )

Transcription

1 Hydrologic Analysis Techniques ( 87 Manual Hydrology Tools )

2 Objectives Know which wetland applies to which technique Define the Wetland Water Budget Locate data Understand the time step Understand Limitations

3 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 Slide 3

4 Probabilities (What does in a normal year mean?) 50% chance can be: Median Middle number in a population 2-yr Log-Pearson Commonly used for return period of annual peak discharges 50 th Percentile Calculated from a Weibull Plot Slide 4

5 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 Slide 5

6 Simplified Water Budgeting I O = ΔS (Inflow Outflow = Change in Storage) Inflows and Outflows: P = Precipitation R i = Surface Runoff in R o = Surface Runoff out G i = Groundwater discharge in G o = Groundwater recharge out ET = Evapotranspiration

7 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

8 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

9 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) R o 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 G i neglected, G o stops when profile is saturated

10 Monthly Precipitation, P WETS Table Tables

11 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

12 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

13 Surface Runoff Runoff Curve Number Method Curve Numbers Meant for use with daily rainfall Must convert RCN to CN 30 for use with monthly rainfall This method used by the AWM program for feedlot runoff The CN 30 is the 30 day Curve Number CN 30 = CN 1 (CN 1 ((CN1^2.365)/631.79) - 15) log 30 CN of 85 = CN 30 of 67

14 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 CN 30 = 67

15 Solution:

16 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

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18 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.

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20 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

21 File Edit Options Data Projects Field/Pond View Window Help/Tutorial MAIN SCREEN

22 Agricultural Field Hydrology

23 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

24 FIELD Data Inputs Climate: Precip., evap., temp. Crop: Canopy, greeness, roots Soil: depths, textures Management: crop rotations, irrigation

25 Graphical Output Select Variable: Daily Precip. Accum. Precip. Daily runoff Accum. runoff

26 Wetland / Pond / Reservoir

27 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.

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

29 POND Graphical Output Select Variable: Daily Precip. Pond Depth Accum. Evap. Accum. seepage

30 Wetland Statistical Analyses 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 DEPTH (FT): DRY AREA (AC): YEARS (%) : 84% 84% 74% 61% 52% 52% 45% 29% 19% 6% 0%

31 Stream Gage Data Analysis Long Term Ponding Riverine HGM Class Wetland Sites Temporary Flooding Slide 31

32 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

33 Will flood inundation analysis work in your Area? Daily Mean Flow Data is the Default Daily Peak and Minimum Data Sometimes Available Daily Stage Sometimes Available Slide 33

34 Will it work in your Area? Typical Peak Duration? Slide 34

35 Will it work in your Area? Web Soil Survey Flooding Duration Brief 2 to < 7 days Frequency Frequent - >50 times in 100 years Slide 35

36 Western Snowmelt Hydrographs Long Durations But low peaks Slide 36

37 Other Parameters - Peak Discharges Instantaneous Peak Discharges (50% Chance Annual Probability) Fill Floodplain Depressions (Duration from Water Budgeting) Slide 37

38 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

39 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

40 USGS Qualitative Adjectives Assigned to Mean Daily Discharges Excellent - 95% of Daily Discharge Within 5% of Rating Curve Good Fair Poor - 95% of Daily Discharge Within 10% of Rating Curve - 95% of Daily Discharge Within 15% of Rating Curve - Daily Discharges Have Less than Fair Accuracy

41 Data Requirements Flow Data Mean Daily Flow File Gage Datum Slide 41

42 Data Requirements Flow Data Order: Text File, Tab-delimited Can open in Spreadsheet Flow Date Slide 42

43 Data Requirements Channel Rating Gage Height Flow Slide 43

44 NRCS Guidance on Rating Curves Slide 44

45 Site Topography USGS Quad Maps James Huron, South Dakota 15-day, 50% chance Flow obviously Exceeds 10 ft. floodplain contour Site Gage Station Slide 45

46 Water Surface Profiles HEC-GeoRAS Product Slide 46

47 Determine Lowest Flow/Stage for Each Duration 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

48 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

49 Procedures Continued If 50% Chance is Discharge, Relate it to Elevation If Available, Use Computerized Stream Flow Data Determine Area Inundated Critical Duration

50 Day Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

51 Day Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

52 Day Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

53 Day Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

54 Day Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

55 Day Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

56 Year Discharge

57 Rank Discharges

58 Year Discharge Ranked

59 Year Discharge Ranked

60 Year Discharge Ranked Median Value = ( )/2 = 759 cfs

61 Exercise 1. Determine elevation from rating curve 2. Draw Contour on Map 3. What is your answer?

62 HEC Ecosystem Functions Model (EFM) Slide 62

63 Slide 63

64 Slide 64

65 Slide 65

66 Observation Wells

67 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

68 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

69 Site Evaluation Start with a good soil profile description Respect all impermeable layers Plug any holes into or through with impermeable material

70 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.

71 ENDOSATURATION >=200 cm 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.

72 <200cm EPISATURATION <200cm Top of unsaturated zone - 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.

73 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?

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

75 Impermeable layer Piezometers typically installed in confined aquifers for g.w. flow.

76 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.

77 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.

78 Perched Artesian, confined aquifer Ground water flow 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.

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

80 Problems Often Encountered with Observation Wells: 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)

81 Problems Often Encountered with Observation Wells (cont.) 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)

82 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.

83 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

84 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)

85 Drainage Equations

86 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

87 Drainage Equations Apply Directly to MINERAL FLAT Wetlands All water budget vectors are vertical before drainage Drainage introduces horizontal flow

88 Effects of Drainage Systems Estimate the lateral effect of a ditch or subsurface drain on the water table

89 Typical application of observation wells, drainage equations, DRAINMOD ENDOSATURATION

90 Drainage Equations Ellipse Hooghoudt (used in DRAINMOD) van Schilfgaarde Kirkham - removal of surface water (used in DRAINMOD)

91 Figure 1: Example Using The Ellipse Equation m=d-c S = [(4K) (m 2 + 2am) / q] 1/2

92 Ellipse Equation S = [(4K) (m 2 + 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

93 How do we get Lateral Effect out of this? m=d-c Le = S / 2

94 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

95 K1 T1 K2 T2 Drainage K3 T3 Feature Soil A K1 K2 T1 T2 K1 K2 Soil B T1 T2 Choose more restrictive: Soil A or B Drainage K3 T3 K3 T3 Feature

96 Example Problem K = 1.3 in/hr K = 0.9 in/hr 12 in 48 in What hydraulic conductivity do we use? K = 0.15 in/hr 52 in

97 Answer K = 1.3 in/hr * 12 in in/hr * 48 in 60 in K = 0.98 in/hr

98 Ellipse Equation S = [(4K) (m 2 + 2am) / q] 1/2

99 q = q is the drainage rate How much water needs to be removed by when?

100 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 = in/day

101 Table 1. Drainable Porosity for Commerce Soil Water Table Depth of water Drainable Depth Drained Porosity 0 - Depth (cm) (cm) (cm/cm) N/A 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

102 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)

103 Example: Calculate Drainable porosity to 30 cm Water Table Depth of water Drainable Depth Drained Porosity 0 - Depth (cm) (cm) (cm/cm) N/A

104 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 cm)/(0 cm-30 cm) = ( cm)/(-30 cm) = cm/cm

105 Example 2. The drainable porosity if the water table is lowered from 10 cm to 30 cm is: Drainable Porosity = ( cm cm)/(10 cm-30 cm) = ( cm) / (-20 cm) = cm / cm

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

107 Where do you get the Soil data?

108 1.Field Data - Collect soil samples and perform laboratory analysis. Or, 2. NRCS National Soil Information System (NASIS database) % Sand, Silt, and Clay Water 33 kpa and 1500 kpa Moist Bulk density Depth to top and bottom of each layer

109 Rosetta Model (ARS, Riverside, CA) Rosetta uses Pedotransfer functions and the information from the NASIS database to predict: water retention Hydraulic conductivity

110 Values from ROSETTA Class Averages Texture Drained f Ksat Class Vol@30 cm 0-30 cm (cm) (cm/cm) (cm/hr) Clay C Loam Loam L Sand Sand S Clay S C L S Loam Silt Si Clay Si C L Si Loam

111 Hooghoudt Equation S ' = (8K am + 2 4K m 1 2 / q K 1 = weighted hydraulic conductivity above the drainage feature, in/hr K 2 = weighted hydraulic conductivity below the drainage feature, in/hr Note: K 1 and K 2 do not have to be different (also uses an equivalent depth that will be discussed later)

112 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.

113 van Schilfgaarde Equation S = drain spacing m = height of water table above the center of the drain at midplane after time t, ft m 0 = initial height of water table above the center of the drain at t = 0, ft t = time for water table to drop from m 0 to m, days a = depth from free water surface in drainage feature to impermeable layer, ft f = modified drainable porosity d e = equivalent depth

114 f modified drainable porosity f = f + (s/(m o m) s = water trapped on the surface by soil roughness, ft s = ft (0.1 in) would be typical Note: set s = 0 if unsure of appropriate value

115 Surface Ponding (Microtopography) Average depth of storage that occurs before runoff begins. Distributed across the field - average

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

117 Surface Storage Depths Well graded cropland Fair cropland Pasture Improved Forest Native Forest Surface Storage Description 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. 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. 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. 1.5 to 3.0 cm Depressions of varying depth. 2.5 to 5.0 cm Many depressions of varying depth. Widespread ponding that can last for days.

118 Ponding Natural Microtopography

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120 Kirkham s Equation Kirkham s Equation for Parallel Drains For removal of ponding only

121 Figure 2: Pothole With Tile Drainage System

122 Kirkham s Equation

123 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

124 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

125 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)

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127 Graphical Output Mineral Flat Willamette Valley, OR Wet Prairie

128 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

129 Questions?