6/25/2012
The Land
&
The Lake
Shoreland Development
&
Water Quality
Paul McGinley
UW-Stevens Point
2012 NW WI Lakes Conference
June 22, 2012
Overview
• Let’s discuss how the lake and the land
are connected – particularly with
respect to the transfer of nutrients
(such as phosphorus) from the land to
the water.
• We will focus on one aspect of
shoreland effects– the movement of
water and conveyance of phosphorus
• There are other important potential
impacts of shoreland development–
such as the impact of septic systems,
movement of sediment and habitat
considerations
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Overview
• Part I – Intro to the Lake and the Land
• Part 2 – Water Quality – Phosphorus
• Part 3 – The Developed Shore
The Lake
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200 acre
10’ average
650,000,000 gallons
200 acre
10’ average
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• Where did this water come from?
• Where does it go?
The Land (the watershed)
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1000 acres (example)
32”/year
Baseflow
Event Flow
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32”/year
Evapotranspiration (22”/year)
Baseflow
Event Flow
32”/year
Evapotranspiration (22”/year)
Baseflow
Event Flow
Flow out of watershed = 10”/year
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32”/year
Evapotranspiration (22”/year)
Baseflow
Event Flow
Flow out of watershed = 10”/year
= 270,000,000 gallons/year
270 million gallon/year
650 million gallons
in lake
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270 million gallon/year
650 million gallons
In lake
Recap– Part I
• There is a lot of water moving through our
lakes
• Almost all of the water in a lake has passed
through land first
• Water “connects” the lake to the land
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Water Quality
• Definitions
• Let’s look at phosphorus
PO43-
Water Quality
• Definitions
• Let’s look at phosphorus
PO43-
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Assume 40 microgram P/l
Assume 40 microgram P/l
That’s 217 pounds P in the water
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How about the land?
Let’s start with 1 acre
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70 lb plant P
80 lb organic matter P
400 lbs soil P (top 6”)
550 lb P
/acre
Adapted from Yanai, R.D., 1992. Phosphorus Budget of a 70-year-old northern hardwood forest
Biogeochemistry 17:1-22
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1000 acre watershed = 550,000 lb P
200 acre lake = 217 lb P
Just the first couple hundred feet around
the lake could be more than 30,000 lbs
200 acre lake = 217 lb P
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Recap Part II
• A lake contains 100’s of pounds of phosphorus
• The land contains 100,000’s of pounds of
phosphorus
• Remember… a lot of water moves from land to
lake
• Why isn’t there more phosphorus in the lake?
The Developed Shore--Phosphorus
Chemistry & Biology
• Very reactive
• Incorporated quickly
• 1) Percolate through soil– lots of time for
reaction & filtering
• 2) Run across soil—little time for reaction
and little filtering
• Let’s follow the water
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A lot of details
- how much rain / over what time
- amount of impervious area
- dimensions of run-on area
- infiltration characteristics
Inches / 10 min
0.2
Rain
0.1
0.0
0
10
20
30
40
50
60
Minutes
Run-on
Runoff
•
•
•
Source Area: 500 ft2
Run-on Area: 40 ft x 5 ft
Hourly time-step
•
•
Compute Runoff as f (storm and infiltration)
Annual hourly rainfall to estimate connection
A few experiments
Runoff Volume over Time
Volume
(liter)
20
18
16
14
12
10
5
7
8
3
6
4
2
0
0
50
100
150
200
250
300
350
400
Time (sec)
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Let’s look at the importance of storm size & infiltration rate
How much water runs off?
First--- what size of storm? Look at typical hourly precipitation
1000
Hours / Year
100
¼ inch/hour
10
1
0.1
0.01
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
1
1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9
2
Inches / Hour
Based on P8 hourly rainfall
File for 36 years, Madison
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1000
Hours / Year
100
½ inch/hour
10
1
0.1
0.01
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
1
1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9
2
Inches / Hour
Based on P8 hourly rainfall
File for 36 years, Madison
Second… how fast does the water
infiltrate (percolate) into the ground?
Measure in inches/hour
Typical range?
What controls this?
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Fraction of Runon That
Runs Off
Then combine that with different soil infiltration rates
1.5
1.3"
¼ - ½ inch/hour
1
0.5"
0.5
0.25"
0.1"
0
0.01
0.1
1
10
Infiltration Rate (in/hr)
The fraction of runon to the secondary buffer that would infiltrate for different
storm sizes and infiltration rates (assumes a 500 ft2 impervious area draining to a
five foot wide channel, forty feet long and one hour storm of depth shown).
Dashed lines show the fitted equation based on soil infiltration rate and storm
depth.
Runon Ratio
500 / 5(w) x 40 (L)
Fraction of Runon That
Runs Off
What controls the infiltration rate?
1.5
CLAYEY
SILTY
SANDY
1.3"
¼ - ½ inch/hour
1
0.5"
0.5
0.25"
0.1"
0
0.01
0.1
1
10
Infiltration Rate (in/hr)
Runon Ratio
500 / 5(w) x 40 (L)
The fraction of runon to the secondary buffer that would infiltrate for different
storm sizes and infiltration rates (assumes a 500 ft2 impervious area draining to a
five foot wide channel, forty feet long and one hour storm of depth shown).
Dashed lines show the fitted equation based on soil infiltration rate and storm
depth.
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Factors Controlling Water Movement
What about compaction?
Condition
Ponded
Infiltration
Rate (in/hr)
Vegetated
3.4
Open Soil
0.7
Traffic
0.1
Silt loam soil described by
Vervoort, R.W., S.M. Dabney and
M.J.M. Romkens. 2001. Tillage and Row
Position Effects on Water and Solute
Infiltration Characteristics, Soil Science
Society of America Journal 65:1227-1234.
Let’s go back to our lake
(let’s make it just a bit more complex…
say ~180 lb/year into the lake will
maintain about 217 lb in the lake)
180 lb P/year
90 lb/yr
217 lb P
90 lb/yr
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Back of the envelope comparison
groundwater versus surface runoff
1 mg/l
0.02 mg/l
Back of the envelope comparison
groundwater versus surface runoff
1 mg/l
10 inches/year
0.02 mg/l
2.3 pound/acre/yr
0.05 pound/acre/yr
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Back of the envelope comparison
groundwater versus surface runoff
10 inches/year
1 mg/l
0.02 mg/l
2.3 pound/acre/yr
0.05 pound/acre/yr
2300 lb/1000 acres
50 lb/1000 acres
Then why so complicated?
Taken from
McGinley et al
Presented at the
WI-AWRA Conf
March 2010
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Summary
• Water connects land and water
• Land is a concentrated source of nutrients
• Increase overland flow paths– increase
concentration of P – increase phosphorus
transfer
Recommendations
• Make it hard for the water
to get to the lake
• Increase infiltration rates
and direct runoff to high
infiltration areas
• Don’t compact
• Don’t shape to the lake
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Let’s keep talking
• Paul McGinley
• (715) 346-4501
• paul.mcginley@uwsp.edu
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