Transcript Soil and Water Management

2015 PE Review:
Soil & Water Management
Michael C. Hirschi, PhD, PE, CPESC, D.WRE
Senior Engineer
Waterborne Environmental, Inc.
[email protected]
also Professor Emeritus
University of Illinois
Acknowledgements:
Chris Henry, I-C PE Review (2006-2009)
Rod Huffman, past PE Review coordinator
Session Topics
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Soil & Water Basics Review
Evapotranspiration
Subsurface Drainage
Irrigation
Nutrient Management
S&W Basics Review
• Soil makeup
• Infiltration & soil-water
• Soil-Water-Plant Relations
Subsurface Drainage
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Basic issues
Design considerations
System sizing
System installation
Irrigation
• Plant water use
• Types of irrigation
– Sprinkler
– Flood
– Drip
• Design considerations
Nutrient Management
• Soil loadings
• Application issues
A few comments
• Material outlined is about 3 weeks or more in a
3-semester hour class. I’m compressing at least
6 hours of lecture and 3 laboratories into 2
hours, so I will:
– Review highlights and critical points
– Do example problems
• You need to:
– Review and tab references
– Do additional example problems, or at least
thoroughly review examples in references
Basics – Soil Make Up
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Mineral
Water
Air
Organic Matter
Infiltration & soil-water
• Infiltration is the passage of water through the
soil-air interface into pores within the soil matrix
• Movement once infiltrated can be capillary flow
or macropore flow. The latter is a direct
connection from the soil surface to lower
portions of the soil profile because of root holes,
worm burrows, or other continuous opening
• Infiltrated water can reappear as surface runoff
via “interflow” and subsurface drainage
Soil, water, air
The inter-particle space (voids) is filled with
either water or air. The amount of voids
depends upon the soil texture and the
condition (ie. tilled, compacted, etc.).
Water (moisture) content
• Special terms reflect the fraction of voids filled
with water (all vary by texture and condition):
– Saturation: All voids are filled with water
– Field Saturation: Natural “saturated” moisture content
which is lower than full saturation due to air that is
trapped.
– Field capacity: Water that can leave pores by gravity
has done so (0.1 to 0.33 bars)
– Wilting point: Water that is extractable by plant roots
is gone (15 bars)
– Hygroscopic point: Water that can be removed by all
usual means is gone (but some remains, 30 bars)
Saturated (all pores filled)
Field Capacity
(Some air, some water)
Wilting point
(water too tightly held for plant use)
Water States by Soil Texture
Volumetric Water content
60
50
40
Gravitational
30
Plant Available
20
Unavailable
10
0
Sand
Sandy
Loam
Loam
Silt Loam
Clay
Loam
Clay
Any questions on general
soil and water basics?
Evapotranspiration (ET)
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Evaporation
Crop water use
Reference Crops
Pan Evaporation
Crop Coefficients
Evaporation
• Transfer of water from liquid to vapor state
• Tabulated as “lake evaporation” across the
US.
Generally, evaporation
exceeds precipitation
west of the Mississippi
River.
Example
• The mean annual lake evaporation in
inches in Amarillo, TX (panhandle), is
most nearly:
A. 50
B. 65
C. 75
D. 85
Evaporation
Fangmeier et al. (2006), pg 56
Evaporation
The mean annual lake evaporation in inches
in Amarillo, TX (panhandle), is most
nearly:
A. 50
B. 65
= 1900mm/25.4 mm/in = 75 in, so answer is C
C. 75
D. 85
Evapotranspiration (ET)
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Combined Evaporation and Transpiration
Also called “consumptive use”
Useful to predict soil water deficit
Estimation methods (predict ETo, which is
for Reference Crop)
– Evaporation Pan
– Penman-Monteith (see example in Fangmeier
et al., 2006, pages 64-66)
ET vs. Precipitation
Reference Crops
• Alfalfa (comparable to field crops)
• Grass (easy to maintain under weather
station, data can be related to alfalfa data)
Crop Coefficients
• Relate crops at various stages of growth to
reference crops
• ETc = Kc x ETref
Crop Coefficients
Both figures: Fangmeier et al. (2006)
page 70
Crop Coefficients, by crop & stage
Fangmeier et al. (2006)
page 71
Crop growth stages
Fangmeier et al. (2006) page 71
Example
Estimate ETc for corn (maize) in Sioux City,
Iowa if the ETref is 8mm/day on July 1.
Planting date was April 15.
A: 8mm
B: 9mm
C: 10mm
D: 11mm
Solution
ETc = Kc x ETref
Initial growth stage is 20 days, to May 5
Development stage is 40 days, to June 9
Mid stage is 50 days, to July 29
So, on July 15, in Mid-stage, so Kc is 1.2
ETc = Kc x ETref = 1.2 x 9 = 10.8mm, or 11mm (D)
Hint: Follow Fangmeier example 4.4
Any questions on ET?
Drainage
• Removal of excess water
• Benefits include
– More days to work in field
– Less crop stress due to high moisture
– Early germination because of warmer soil
• Liabilities include
– Expense
– Potential water quality issues
– Outlet required, may need pump
Objective of Drainage is
Financial Benefit
• Optimize crop growth
– Increase yield
– Reduce wetness-based disease
– Reduce variability within fields and from year to year
• Improve timeliness of field work
– May use smaller equipment
– May increase acreage
– May reduce labor costs
• Increase value of land
Drainage types
• Surface
– Basic enhancement of flow patterns
– Surface grading/planing
– Surface ditching
• Subsurface
– Irregular
– Regular
• Watertable Management
Subsurface Drainage
• Removes gravitational water only
• Degree of drainage specified as depth/day
• System design dictated by crop, soil,
location, topography and more…
• Can be used to manage watertable down
or up
• Changes hydrologic response of field and
if widely installed, the watershed
HYDROLOGIC CYCLE (with tiles)
Design Considerations
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Soil type
Crop to be grown
Outlet
Topography

Crop Yield
Rate of Return
100
Profitability
Cost or Yield Ratio (%)
Cost/Acre
Tile Density
Spacing
Drainage system design
• Capacity to remove water is expressed as
depth/day (eg. 3/8 in/day)
• Spacing, maximum and minimum depth
(absolute minimum of 24” without special
protection), and maximum and minimum
slope are dictated by soil and topography
Depth/Spacing Choices
Excellent Reference:
ASABE Standards
The material that follows is directly from
ASABE EP480, issued MAR1998 (R2008),
“Design of Subsurface Drains in Humid
Areas”
Drain Spacing
Diagram for Hooghoudt Eq.
Drain Spacing by Hooghoudt Eq
Area
Drained
CPT
Capacity
Example
A subsurface drainage system is to be installed on
a square 160 acres (1/4 section) in East Central
Illinois. The Drainage Coefficient is 3/8”/day and
the Illinois Drainage Guide indicates a 120’
spacing at 4’ depth. The proposed slope is
0.1%. What diameter CPT is needed for each
lateral?
A: 3”
B: 4”
C: 5”
D: 6”
Solution
A square 160 acres is a ½ mile on each side, or
2640’. A spacing of 120’ gives an area for each
lateral of 120x2640 or 316800 sq.ft. If the
system removes 0.375”/day, the flow rate
needs to be
316800ft2*0.375in/day/12in/ft/24hr/day/3600s/hr
or 0.115 cfs.
Enter the chart
Answer: D, 6”
Irrigation
• Supplements rainfall
• Need and design dictated by crop, soil, location,
topography, water availability, energy price, and
more…
• Simplistic description: Use the soil as your water
tank
– Deplete it to some predetermined safe level
– Refill it as needed
– Don’t overtop and waste water (runoff)
• Plant Available Water is soil moisture held
between Field Capacity and Wilting Point.
Irrigation methods
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Sprinkler (entire area is covered)
Surface (flood, furrow)
Drip (trickle, only plant root zone is watered)
Subirrigation
Information needed for design
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Soil texture and profile water storage
Soil infiltration rate
Water source
Available flow and pressure
Water quality
Water cost
Irrigated area
Elevation changes on site
Plants to be irrigated, root depth
Plant water use (inches/day)
Design decisions and specific
computed data needs
• How much do we let the soil-water deplete prior to irrigation
(“management allowed depletion”, MAD, % as decimal, typically 4050%, though can vary depending upon crop and climate)?
• How much water is available to the plant within its root zone (total
amount is “available water”, AW, in inches)?
• How much water will we replace with each irrigation (equal to MAD *
AW or “readily available water”, RAW, in inches)?
• How much total water do we need per irrigation cycle (equal to
RAW*total irrigated area/efficiency)?
• How often do we need to irrigate the same area of plants (“irrigation
interval”, equal to AW/(plant water use, in/day))?
All these concepts and equations are in any basic book or chapter on
irrigation, such as Fangmeier et al. (2006).
Available Water, AW
• Soils vary in their characteristics by depth
• Soil surveys have information on each soil by
depth
• For example, consider the AW with depth for two
Illinois soils (data from WebSoilSurvey):
Layer
Drummer SiCL
Plainfield Sand
0-9”
0.18 in/in
0.07 in/in
9-18”
0.17 in/in
0.06 in/in
18-27”
0.16 in/in
0.06 in/in
27-36”
0.16 in/in
0.06 in/in
AW for Corn
• If we assume a 36” rooting depth for corn
on either soil, we get the following AW:
• Drummer: AW=0.18*9+0.17*9+0.16*18=
6.03”, so 6.0” in root zone
• Plainfield: AW=0.07*9+0.06*27=2.25”, so
2.3” in root zone
Irrigation Interval
• So, given those 2 soils, and corn has a
0.25 in/d water use, if no rain, how many
days before all available water is
depleted?
• Drummer: 6”/.25ipd = 24days
• Plainfield: 2.3”/.25ipd=9days
Now you know why there are many irrigated acres of
Plainfield and few irrigated acres of Drummer
Example
You are designing a sprinkler irrigation system for
a pick-your-own strawberry field. Your
references indicate that strawberries use 0.25
in/day. The soil profile has a field capacity value
of 0.36 in/in and a wilting point value of 0.24
in/in. The rooting depth of strawberries is 9”.
You don’t wish to deplete your soil moisture
below 50% available water. How much will you
irrigate and how often? Assume 100% efficiency
A: 1” every 7 days; B: 0.5” every 2 days; C: 0.25”
every day; D: Not enough information
Solution
Plant available water (AW) in the root zone
is (0.36in/in-0.24in/in)*9in = 1”. The
amount of water you wish to replace is half
that amount (MAD), or 0.5” (RAW), which
is your irrigation depth. Given the
strawberries use 0.25 ipd, you will have to
irrigate 0.5” (irrigation depth) every 2 days
(irrigation interval) if it doesn’t rain.
Answer: B
Lateral Size
• Assume you will use a single lateral of pipe that you are
able to move across the strawberries. It is Schedule 40
PVC and you chose four Rainbird 20JA impact
sprinklers. The technical specs indicate the nozzles
deliver 4.5gpm at 40psi while delivering water to a radius
of 40’. Your plan for the lateral is to have the 1st
sprinkler at 20’, then at 40’ intervals. What size PVC do
you need between each sprinkler if your planned
variation in pressure from high to low is +/- 10%?
Lateral Size
Use the friction factor equation to determine how much
loss/100’ of pipe is allowable and choose lateral sizes
accordingly:
Ff = (Po)*(Pv)/Lc
Where:
Ff is the maximum pipe friction factor (psi/100’),
Po is the design operating pressure (psi),
Pv is the allowable pressure variation (+/-, as decimal, psi),
and
Lc is the critical length (distance to furthest sprinkler, ft)
Lateral Size
Now, Po is 40psi, Pv is +/- 10% or 0.2 expressed as
decimal, Lc is 20’+40’+40’+40’ = 140’, So, Ff = 40*0.2/140 =
0.057 psi or 0.05 psi
The first section of pipe has flow for all four nozzles, or
18gpm. The next section has three nozzles flow, or
13.5gpm, the last two sections have 9gpm and 4.5gpm,
respectively
Standard tables are available in many texts for pressure
loss in pipes due to friction. Such a standard table is on
the next page (from Rainbird website).
Lateral Size
• So, if we are to keep friction factor at 0.05
psi/100’ or less, we need to begin with 3”
PVC, and it needs to stay 3” after the first
nozzle, but can reduce to 2” after the
second nozzle. If a bit more variation is
OK (eg. +/- 15%, or 0.086psi/100’), the
lateral can reduce to 2-1/2” after the first
nozzle, 2” after the second and 1-1/2” after
the third.
Example
You have determined that you will have to
supply 2” of water every 10 days to meet a
corn field water demand. You will use a
lateral move system to apply the water in a
16-hr period every 10 days. The field in
question is 20 acres (933 feet square).
Assume an 80% sprinkler efficiency. How
much water will you apply each irrigation
and at what flow rate?
Solution
2” every 10 days means volume is
2”/12 in/ft*933ft*933ft = 145081 ft3 or 1,085,200
gal
Prior to efficiency being considered, flow rate is
1,085,200gal/(16hr*60min/hr) or 1130 gpm
At 80% efficiency, 1085200/.8 gal need to be
sprayed or 1,356,500gal for a flow rate of 1413
gpm
Reference Recommendations
• ASABE Standards
• Fangmeier et al. (2006) or Schwab et al.
(1993)
• MWPS Sprinkler Irrigation Manual
Questions on irrigation?
Nutrient Management
•
One feeder pig produces 10.3 lbs of manure
per day. Assuming that manure has the same
density as water, how much manure, in cubic
feet, is most nearly produced annually from a
1000 head barn that has 3 sets (or turns) per
year.
a)
b)
c)
d)
40,000
70,000
76,000
257,000
Nutrient Management
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a)
b)
c)
d)
One feeder pig produces 10.3 lbs of manure
per day. Assuming that manure has the same
density as water, how much manure, in cubic
feet, is most nearly produced annually from a
1000 head barn that has 3 sets (or turns) per
year.
40,000
60,000
76,000
257,000
Answer B,
10.3/62.4*1000*365=60,248
Nutrient Management/Facilities
• The maximum loading rate (pounds of
volatile solids per 1000 cubic foot per
day) for an anaerobic lagoon for animal
waste in West Central Illinois is most
nearly:
a) 2.0
b) 3.0
c) 4.0
d) 5.0
Nutrient Management/Facilities
• The maximum loading rate for an
anaerobic lagoon for animal waste in
West Central Illinois is most nearly:
a) 2.0
b) 3.0
C, 4.0, EP403.3
c) 4.0
d) 5.0
Loading of Soils Conversions
K
1.2 K2O
N
4.43 NO3
P
2.29 P2O5
N
1.29 NH4
cu ft
7.48 gallons
Questions?