Analysis: Managed Allowed Depletion

Managed Allowed Depletion is the maximum amount of Plant Available Water (PAW) allowed to be removed from the soil before irrigation refill occurs.

So what is managed allowed depletion?

It is the way plants and lawns are meant to be irrigated.

It is the technique of waiting until the moisture level in the soil is depleted to a predetermined level before applying more water. By watering this way, your plants and grass will be healthier because it will encourage deeper root growth and allow oxygen into the root zone.

To be able to water this way, we need to know where the moisture level is currently, and at what moisture level do we need to water again.

Evapotranspiration processWhere is the moisture level in the soil?

Water is lost from the soil in two ways, evaporation, and transpiration. It is called evapotranspiration (ET).

Evapotranspiration is affected by soil moisture, temperature, solar radiation, humidity, and the wind. By measuring and using this information we can calculate how much water the soil has lost and as a result when we need to irrigate.

Water is added via precipitation either naturally or via irrigation.

We can keep track of the water entering the soil by measuring rainfall and knowing how much water we apply when we irrigate.

How is managed allowed depletion used?

We know how much water is lost each day via evapotranspiration and we know how much water enters the soil via precipitation and irrigation. All we have to do is manage the water depletion.

Based on the type of soil and the depth of the roots there is a fixed amount of water available to the plant. Water that is deeper than the depth of the roots is unavailable to the plant and different soils can hold different amounts of water. Using soil type and root-depth we calculate the maximum amount of water available to the plant, this is called the plant’s available water (PAW).

Depending on the plant type, we manage the amount of plant-available-water (PAW) we allow to be depleted from the soil before we have the irrigation system turn on and replenish the soil.

Typically the managed allowed depletion point is around 50% of the plant-available-water.

How does it compare to timer-based irrigation?

Let’s take a look at two systems, System A and System B. The two systems are identical in every respect except for how the controller operates.

A conventional controller operates on a fixed schedule.

Most clients set their controllers to apply a minimum of 1″ of water per week. That is normally accomplished by applying 0.4″ of water every other day. Most conventional controllers also use rain sensors, so let’s assume this system has a rain sensor that will suspend irrigation if it measures 0.25″ of rain.

An ET controller uses the managed-allowed-depletion technique to plan its own schedule.

It will calculate daily the water requirements of the plant and water accordingly. We assume the grass has roots that are 3″ deep and the managed-allowed-depletion is 50% the PAW.

How would they irrigate?

In this example, we compare the two systems using actual weather from 2016.

System A with the smart controller allows the top 50% of the soil to dry before watering

Because evapotranspiration is heavily dependent on temperature, when the temperatures are low during springtime and autumn, the lawn has no need for additional irrigation. The amount of water that is lost from the soil is easily replenished by natural rainfall.

Because system B overwaters, the soil never dries up more than 0.5″. This prevents oxygen from entering the root zone and hinders the growth of the lawns root system. By stunting the growth of the roots the lawn will be more susceptible to weeds and disease once the heat of summer comes.

The more shallow the root system, the less water the lawn has available to it. With shallow roots, there is even less chance the lawn can wait for natural rainfall and will require irrigation.

System A with the smart controller automatically irrigates if the accumulated water loss reaches the 1.5″ threshold.

This is our managed depletion point for a lawn with a root depth of 3″ and allows oxygen to enter the root zone which promotes even deeper roots and saving water.

System A with the smart controller used 62% less water and increased the health of the lawn

 

Every time a smart controller prevents a watering cycle, it not only saves you water but also reduces the wear and tear on your system.

Don’t forget, in addition to an unhealthy lawn, the conventional controller applied 35.6″ of water to your lawn. That is 21.1″ more than the smart system. That reduces the life of the system in addition to the cost of water.

The amount of water the smart system can save is staggering.

The table below illustrates how much money the smart system would have saved you in 2016 alone versus a conventional controller. The examples given are for lawn sizes of 2,500 sqft, 5,000 sqft, 10,000 sqft, and 15,000 sqft in various municipalities.

System A – (Smart Controller)

DatePrecipitation
(inches)
Temperature
(celcius)
ET (Water Loss)
(inches)
Irrigation
(inches)
Accumulated loss
(inches)
15-Apr-160.00140.1400.14
16-Apr-160.00170.1500.29
17-Apr-160.00210.1600.45
18-Apr-160.00240.2600.71
19-Apr-160.00270.2000.92
20-Apr-160.00180.2101.12
21-Apr-160.00230.2101.33
22-Apr-160.00140.1301.47
23-Apr-160.0080.041.50.00
24-Apr-160.0270.0400.02
25-Apr-160.0250.0300.03
26-Apr-160.00110.0900.12
27-Apr-160.00120.1200.23
28-Apr-160.00110.1200.35
29-Apr-160.00120.1200.47
30-Apr-160.00140.1000.57
1-May-160.00210.1600.73
2-May-160.00260.2200.95
3-May-160.00280.2401.18
4-May-160.00270.2401.42
5-May-160.00190.161.50.09
6-May-160.00200.1800.27
7-May-160.00280.2800.55
8-May-160.03190.1800.70
9-May-160.00110.1400.84
10-May-160.00130.1601.01
11-May-160.00150.1501.16
12-May-160.1980.0501.03
13-May-160.00110.1201.14
14-May-160.00150.1601.30
15-May-160.00180.1801.48
16-May-160.00210.231.50.22
17-May-160.00240.2100.42
18-May-160.00240.2100.63
19-May-160.28140.0800.44
20-May-160.0790.0800.45
21-May-160.3570.0300.13
22-May-160.6350.0300
23-May-160.0490.0700.03
24-May-160.00160.1500.19
25-May-160.00210.1900.37
26-May-160.01200.1500.52
27-May-160.35120.0700.24
28-May-160.00160.1500.39
29-May-160.25200.1900.33
30-May-160.17150.1600.32
31-May-160.00180.1700.50
1-Jun-160.00220.1800.67
2-Jun-160.00230.2300.91
3-Jun-160.00250.2501.15
4-Jun-160.00260.2501.40
5-Jun-160.00250.251.50.15
6-Jun-160.00300.2900.44
7-Jun-160.00290.2800.72
8-Jun-160.00270.2300.95
9-Jun-160.00240.2601.21
10-Jun-160.15160.1001.17
11-Jun-160.07190.2001.30
12-Jun-160.00200.261.50.06
13-Jun-160.00210.2300.29
14-Jun-160.02180.1800.45
15-Jun-160.00170.2300.68
16-Jun-160.00170.2000.88
17-Jun-160.00200.2401.12
18-Jun-160.00200.1801.30
19-Jun-160.13220.2101.38
20-Jun-160.00230.231.50.10
21-Jun-160.01230.2300.31
22-Jun-160.00240.2200.53
23-Jun-160.00230.1900.73
24-Jun-160.81200.1400.05
25-Jun-160.22210.1800.01
26-Jun-160.05210.1700.13
27-Jun-160.01250.2300.35
28-Jun-160.07240.1700.44
29-Jun-160.01250.1900.63
30-Jun-160.49230.1500.29
1-Jul-160.00230.1800.46
2-Jul-160.00230.1800.64
3-Jul-160.05240.2000.79
4-Jul-160.23200.1700.73
5-Jul-160.18180.1300.67
6-Jul-160.00200.1600.84
7-Jul-160.00220.1901.02
8-Jul-160.00240.2201.24
9-Jul-160.26210.1301.11
10-Jul-160.00200.1701.28
11-Jul-160.69200.1500.74
12-Jul-160.06210.1500.84
13-Jul-160.19190.1300.78
14-Jul-160.66190.1300.25
15-Jul-161.42140.0400
16-Jul-160.07170.1100.03
17-Jul-160.38200.1400
18-Jul-160.15230.1600.01
19-Jul-160.00250.2400.24
20-Jul-160.00250.2600.50
21-Jul-160.00260.2300.73
22-Jul-160.00220.1300.86
23-Jul-160.00240.1901.05
24-Jul-160.00250.2001.25
25-Jul-160.30240.1701.12
26-Jul-160.00250.1701.29
27-Jul-160.00260.1801.47
28-Jul-160.52260.1601.11
29-Jul-160.00250.1901.30
30-Jul-161.00240.1600.45
31-Jul-160.31190.1300.27
1-Aug-160.00220.1800.45
2-Aug-160.28230.1700.34
3-Aug-160.63170.0800
4-Aug-160.00220.1600.16
5-Aug-160.00240.1800.34
6-Aug-160.99180.0700
7-Aug-160.14220.1300
8-Aug-160.00210.1300.13
9-Aug-160.00230.1700.29
10-Aug-160.19190.0600.16
11-Aug-160.17220.1300.13
12-Aug-160.00220.1500.28
13-Aug-160.00250.1500.42
14-Aug-160.15250.1500.43
15-Aug-160.00250.1700.60
16-Aug-160.00280.1800.77
17-Aug-160.00210.1200.89
18-Aug-160.01180.1100.99
19-Aug-160.00210.1501.14
20-Aug-160.00250.1601.30
21-Aug-160.00280.1801.48
22-Aug-160.13160.1201.47
23-Aug-160.02160.101.50.05
24-Aug-160.00190.1500.20
25-Aug-160.07180.1100.24
26-Aug-160.00210.1300.37
27-Aug-160.04240.1400.47
28-Aug-160.00140.1000.57
29-Aug-160.00240.1400.71
30-Aug-160.00260.1600.88
31-Aug-160.00280.1501.03
1-Sep-160.00260.2001.23
2-Sep-160.09150.0701.21
3-Sep-160.01190.1301.33
4-Sep-160.00120.0501.38
5-Sep-160.11170.1001.37
6-Sep-160.00160.0801.44
7-Sep-160.00200.121.50.06
8-Sep-160.15150.1000.01
9-Sep-160.00180.1200.13
10-Sep-160.05220.1500.24
11-Sep-160.3390.0400
12-Sep-160.00120.0900.09
13-Sep-160.00190.1300.22
14-Sep-160.00230.1200.34
15-Sep-160.00230.1300.47
16-Sep-160.00240.1300.60
17-Sep-160.00210.1300.73
18-Sep-160.00180.1400.87
19-Sep-160.00170.1100.98
20-Sep-160.0170.0301.00
21-Sep-160.00130.0601.06
22-Sep-160.09100.0201.00
23-Sep-160.00170.1001.10
24-Sep-160.00160.1001.20
25-Sep-160.00200.1201.31
26-Sep-160.00240.1201.44
27-Sep-160.00190.121.50.06
28-Sep-160.00130.0700.13
29-Sep-160.00160.0700.19
30-Sep-160.00170.0700.26
1-Oct-160.13110.0200.15
2-Oct-160.00140.0800.23
3-Oct-160.00140.0700.30
4-Oct-160.00120.0700.36
5-Oct-160.0040.0400.40
6-Oct-160.0060.0500.45
7-Oct-160.1100.0200.37
8-Oct-160.0420.0100.34
9-Oct-160.1330.0300.24
10-Oct-160.0800.0200.18
11-Oct-160.0030.0400.22
12-Oct-160.00100.0500.27
13-Oct-160.00120.0400.31
14-Oct-160.0860.0300.26
15-Oct-160.0050.0300.29
16-Oct-160.00150.0800.37
17-Oct-160.0130.0100.37
18-Oct-160.0120.0000.36
19-Oct-160.00140.0600.42
20-Oct-160.00140.0700.49
21-Oct-160.00120.0600.54
22-Oct-160.00130.0700.62
23-Oct-160.00110.0400.65
24-Oct-160.0040.0100.66
25-Oct-160.00140.0500.72
26-Oct-160.00100.0300.75
27-Oct-160.00150.0700.82
28-Oct-160.2740.0100.56
29-Oct-160.0040.0100.57
30-Oct-160.00130.0600.63
31-Oct-160.0050.0100.64
1-Nov-160.0080.0200.66

System B – (Conventional Controller)

DatePrecipitation
(inches)
Temperature
(celcius)
ET (Water Loss)
(inches)
Irrigation
(inches)
Accumulated loss
(inches)
15-Apr-160.00140.140.00.14
16-Apr-160.00170.150.40.00
17-Apr-160.00210.160.00.16
18-Apr-160.00240.260.40.02
19-Apr-160.00270.200.00.22
20-Apr-160.00180.210.40.03
21-Apr-160.00230.210.00.24
22-Apr-160.00140.130.40.00
23-Apr-160.0080.040.00.04
24-Apr-160.0270.040.40.00
25-Apr-160.0250.030.00.01
26-Apr-160.00110.090.40.00
27-Apr-160.00120.120.00.12
28-Apr-160.00110.120.40.00
29-Apr-160.00120.120.00.12
30-Apr-160.00140.100.40.00
1-May-160.00210.160.00.16
2-May-160.00260.220.40.00
3-May-160.00280.240.00.24
4-May-160.00270.240.40.08
5-May-160.00190.160.00.24
6-May-160.00200.180.40.03
7-May-160.00280.280.00.31
8-May-160.03190.180.40.06
9-May-160.00110.140.00.20
10-May-160.00130.160.40.00
11-May-160.00150.150.00.15
12-May-160.1980.050.40.00
13-May-160.00110.120.00.12
14-May-160.00150.160.40.00
15-May-160.00180.180.00.18
16-May-160.00210.230.40.02
17-May-160.00240.210.00.22
18-May-160.00240.210.40.03
19-May-160.28140.080.00.00
20-May-160.0790.080.40.00
21-May-160.3570.030.00.00
22-May-160.6350.030.00.00
23-May-160.0490.070.00.03
24-May-160.00160.150.40.00
25-May-160.00210.190.00.19
26-May-160.01200.150.40.00
27-May-160.35120.070.00.00
28-May-160.00160.150.40.00
29-May-160.25200.190.00.00
30-May-160.17150.160.40.00
31-May-160.00180.170.00.17
1-Jun-160.00220.180.40.00
2-Jun-160.00230.230.00.23
3-Jun-160.00250.250.40.08
4-Jun-160.00260.250.00.32
5-Jun-160.00250.250.40.17
6-Jun-160.00300.290.00.46
7-Jun-160.00290.280.40.34
8-Jun-160.00270.230.00.58
9-Jun-160.00240.260.40.44
10-Jun-160.15160.100.00.40
11-Jun-160.07190.200.40.13
12-Jun-160.00200.260.00.38
13-Jun-160.00210.230.40.22
14-Jun-160.02180.180.00.38
15-Jun-160.00170.230.40.21
16-Jun-160.00170.200.00.41
17-Jun-160.00200.240.40.24
18-Jun-160.00200.180.00.42
19-Jun-160.13220.210.40.10
20-Jun-160.00230.230.00.33
21-Jun-160.01230.230.40.14
22-Jun-160.00240.220.00.36
23-Jun-160.00230.190.40.15
24-Jun-160.81200.140.00.00
25-Jun-160.22210.180.00.00
26-Jun-160.05210.170.00.12
27-Jun-160.01250.230.40.00
28-Jun-160.07240.170.00.10
29-Jun-160.01250.190.40.00
30-Jun-160.49230.150.00.00
1-Jul-160.00230.180.40.00
2-Jul-160.00230.180.00.18
3-Jul-160.05240.200.40.00
4-Jul-160.23200.170.00.00
5-Jul-160.18180.130.40.00
6-Jul-160.00200.160.00.16
7-Jul-160.00220.190.40.00
8-Jul-160.00240.220.00.22
9-Jul-160.26210.130.00.09
10-Jul-160.00200.170.00.26
11-Jul-160.69200.150.00.00
12-Jul-160.06210.150.00.10
13-Jul-160.19190.130.40.00
14-Jul-160.66190.130.00.00
15-Jul-161.42140.040.00.00
16-Jul-160.07170.110.00.03
17-Jul-160.38200.140.00.00
18-Jul-160.15230.160.00.01
19-Jul-160.00250.240.40.00
20-Jul-160.00250.260.00.26
21-Jul-160.00260.230.40.09
22-Jul-160.00220.130.00.22
23-Jul-160.00240.190.40.01
24-Jul-160.00250.200.00.21
25-Jul-160.30240.170.00.08
26-Jul-160.00250.170.00.24
27-Jul-160.00260.180.40.02
28-Jul-160.52260.160.00.00
29-Jul-160.00250.190.40.00
30-Jul-161.00240.160.00.00
31-Jul-160.31190.130.00.00
1-Aug-160.00220.180.00.18
2-Aug-160.28230.170.00.07
3-Aug-160.63170.080.00.00
4-Aug-160.00220.160.40.00
5-Aug-160.00240.180.00.18
6-Aug-160.99180.070.00.00
7-Aug-160.14220.130.00.00
8-Aug-160.00210.130.40.00
9-Aug-160.00230.170.00.16
10-Aug-160.19190.060.40.00
11-Aug-160.17220.130.00.00
12-Aug-160.00220.150.40.00
13-Aug-160.00250.150.00.15
14-Aug-160.15250.150.40.00
15-Aug-160.00250.170.00.17
16-Aug-160.00280.180.40.00
17-Aug-160.00210.120.00.12
18-Aug-160.01180.110.40.00
19-Aug-160.00210.150.00.15
20-Aug-160.00250.160.40.00
21-Aug-160.00280.180.00.18
22-Aug-160.13160.120.40.00
23-Aug-160.02160.100.00.08
24-Aug-160.00190.150.40.00
25-Aug-160.07180.110.00.04
26-Aug-160.00210.130.40.00
27-Aug-160.04240.140.00.10
28-Aug-160.00140.100.40.00
29-Aug-160.00240.140.00.14
30-Aug-160.00260.160.40.00
31-Aug-160.00280.150.00.15
1-Sep-160.00260.200.40.00
2-Sep-160.09150.070.00.00
3-Sep-160.01190.130.40.00
4-Sep-160.00120.050.00.05
5-Sep-160.11170.100.40.00
6-Sep-160.00160.080.00.08
7-Sep-160.00200.120.40.00
8-Sep-160.15150.100.00.00
9-Sep-160.00180.120.40.00
10-Sep-160.05220.150.00.10
11-Sep-160.3390.040.00.00
12-Sep-160.00120.090.00.09
13-Sep-160.00190.130.40.00
14-Sep-160.00230.120.00.12
15-Sep-160.00230.130.40.00
16-Sep-160.00240.130.00.13
17-Sep-160.00210.130.40.00
18-Sep-160.00180.140.00.14
19-Sep-160.00170.110.40.00
20-Sep-160.0170.030.00.02
21-Sep-160.00130.060.40.00
22-Sep-160.09100.020.00.00
23-Sep-160.00170.100.40.00
24-Sep-160.00160.100.00.10
25-Sep-160.00200.120.40.00
26-Sep-160.00240.120.00.12
27-Sep-160.00190.120.40.00
28-Sep-160.00130.070.00.07
29-Sep-160.00160.070.40.00
30-Sep-160.00170.070.00.07
1-Oct-160.13110.020.40.00
2-Oct-160.00140.080.00.08
3-Oct-160.00140.070.40.00
4-Oct-160.00120.070.00.07
5-Oct-160.0040.040.40.00
6-Oct-160.0060.050.00.05
7-Oct-160.1100.020.40.00
8-Oct-160.0420.010.00.00
9-Oct-160.1330.030.40.00
10-Oct-160.0800.020.00.00
11-Oct-160.0030.040.40.00
12-Oct-160.00100.050.00.05
13-Oct-160.00120.040.40.00
14-Oct-160.0860.030.00.00
15-Oct-160.0050.030.40.00
16-Oct-160.00150.080.00.08
17-Oct-160.0130.010.40.00
18-Oct-160.0120.000.00.00
19-Oct-160.00140.060.40.00
20-Oct-160.00140.070.00.07
21-Oct-160.00120.060.40.00
22-Oct-160.00130.070.00.07
23-Oct-160.00110.040.40.00
24-Oct-160.0040.010.00.01
25-Oct-160.00140.050.40.00
26-Oct-160.00100.030.00.03
27-Oct-160.00150.070.40.00
28-Oct-160.2740.010.00.00
29-Oct-160.0040.010.40.00
30-Oct-160.00130.060.00.06
31-Oct-160.0050.010.40.00
1-Nov-160.0080.020.00.02

 

 

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