Transcript of 2012 PE Review: S&W Management Michael C. Hirschi, PhD, PE, D.WRE Senior Engineer Waterborne...
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2012 PE Review: S&W Management Michael C. Hirschi, PhD, PE,
D.WRE Senior Engineer Waterborne Environmental, Inc.
[email protected] also Professor Emeritus University of
Illinois
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Acknowledgements: Chris Henry, I-C PE Review (2006-2009) Rod
Huffman, PE Review coordinator (thru 2011)
A few comments Material outlined is about 3 weeks or more in a
3-semester hour class. Im 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
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Basics Soil Make Up Mineral Water Air Organic Matter
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Mineral Component - Particles Sand Silt Clay Aggregates Silt
& Sand sizes Less dense than primary particles
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Particle Size Classifications
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USDA Texture Triangle
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Example After soil sample dispersal to ensure only primary
particles are measured, a sample is determined to be 20% clay, 30%
silt and 50% sand. What is the USDA soil texture? A: Sandy Clay
Loam B: Sandy Loam C: Loam D: Clay Loam
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Solution Answer: C, Loam 20% Clay 30% Silt
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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
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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.).
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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)
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Soil Water Holding Capacity (inches-water/foot-soil)
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Water States by Soil Texture Gravitational Plant Available
Unavailable
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Commentary Later, when we discuss drainage, it is the
gravitational water that is of interest, eg. saturation down to
field capacity. The volume of this water, the hydraulic
characteristics of the soil in question, and the wet-
condition-tolerance and value of the crop being grown dictate the
drainage system design and its feasibility. When we consider
irrigation, plant available water (AW) is that held between field
capacity and wilting point. It is this water that we manage via
irrigation to supply water to plants. The volume of AW the soil can
hold within the crop root-zone, the crop value and water use, and
the crop tolerance of dry conditions dictate irrigation design and
feasibility.
Evapotranspiration (ET) Evaporation Crop water use Reference
Crops Pan Evaporation Crop Coefficients
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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.
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Example The mean annual lake evaporation in inches in Amarillo,
TX (panhandle), is most nearly: A.50 B.65 C.75 D.85
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Evaporation Fangmeier et al. (2006), pg 56
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Evaporation The mean annual lake evaporation in inches in
Amarillo, TX (panhandle), is most nearly: A.50 B.65 C.75 D.85 =
1900mm/25.4 mm/in = 75 in, so answer is C
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Evapotranspiration (ET) Combined Evaporation and Transpiration
Also called consumptive use Useful to predict soil water deficit
Estimation methods (predict ET o, which is for Reference Crop)
Evaporation Pan Penman-Monteith (see example in Fangmeier et al.,
2006, pages 64-66)
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ET vs. Precipitation
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Reference Crops Alfalfa (comparable to field crops) Grass (easy
to maintain under weather station, data can be related to alfalfa
data)
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Crop Coefficients Relate crops at various stages of growth to
reference crops ET c = K c x ET ref
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Crop Coefficients Both figures: Fangmeier et al. (2006) page
70
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Crop Coefficients, by crop & stage Fangmeier et al. (2006)
page 71
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Crop growth stages Fangmeier et al. (2006) page 71
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Example Estimate ET c for corn (maize) in Sioux City, Iowa if
the ET ref is 8mm/day on July 1. Planting date was April 15. A: 8mm
B: 9mm C: 10mm D: 11mm
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Solution ET c = K c x ET ref 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 K c is 1.2 ET c =
K c x ET ref = 1.2 x 9 = 10.8mm, or 11mm (D) Hint: Follow Fangmeier
example 4.4
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Any questions on ET?
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Drainage Removal of excess water Benefits include More days to
work in field Less crop stress due to high moisture Earlier
germination because of warmer soil Liabilities include Expense
Potential water quality issues Outlet required, may need pump
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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
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
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HYDROLOGIC CYCLE (with tiles)
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Design Considerations Soil type Crop to be grown (value and
response to wet conditions) Outlet Topography
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100 Tile Density Profitability Cost/AcreCrop YieldRate of
Return Cost or Yield Ratio (%) Spacing
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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
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Depth/Spacing Choices
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Excellent Reference: ASABE Standards The material that follows
is directly from ASABE EP480, issued MAR1998 (R2008), Design of
Subsurface Drains in Humid Areas
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Drain Spacing
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Diagram for Hooghoudt Eq.
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Drain Spacing by Hooghoudt Eq
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Area Drained
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CPT Capacity
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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
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Solution A square 160 acres is a 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
316800ft 2 *0.375in/day/12in/ft/24hr/day/3600s/hr or 0.115 cfs.
Enter the chart
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Answer: D, 6
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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
Dont overtop and waste water (runoff) Plant Available Water is soil
moisture held between Field Capacity and Wilting Point.
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Irrigation methods Sprinkler (entire area is covered) Surface
(flood, furrow) Drip (trickle, only plant root zone is watered)
Subirrigation
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Information needed for design 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)
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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 40- 50%, 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).
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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): LayerDrummer SiCLPlainfield Sand 0-90.18
in/in0.07 in/in 9-180.17 in/in0.06 in/in 18-270.16 in/in0.06 in/in
27-360.16 in/in0.06 in/in
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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
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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
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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 dont 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
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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 doesnt rain. Answer: B
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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 1
st 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%?
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Lateral Size Use the friction factor equation to determine how
much loss/100 of pipe is allowable and choose lateral sizes
accordingly: F f = (P o )*(P v )/L c Where: F f is the maximum pipe
friction factor (psi/100), P o is the design operating pressure
(psi), P v is the allowable pressure variation (+/-, as decimal,
psi), and L c is the critical length (distance to furthest
sprinkler, ft)
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Lateral Size Now, P o is 40psi, P v is +/- 10% or 0.2 expressed
as decimal, L c is 20+40+40+40 = 140, So, F f = 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).
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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.
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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?
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Solution 2 every 10 days means volume is 2/12 in/ft*933ft*933ft
= 145081 ft 3 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
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Reference Recommendations ASABE Standards Fangmeier et al.
(2006) or Schwab et al. (1993) MWPS Sprinkler Irrigation
Manual
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Questions on irrigation?
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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)40,000
b)70,000 c)76,000 d)257,000
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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)40,000
b)60,000 c)76,000 d)257,000 Answer B,
10.3/62.4*1000*365=60,248
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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
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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 d)5.0 C, 4.0, EP403.3