Hello! In our last lesson, we determined the required runtime for each zone by calculating how long it needs to operate to deliver the precise amount of water plants need. For instance, we found our lawn zone might need 33 minutes of water every three days.
This lesson is the final step in our scheduling process. We will take those individual runtimes and organize them into a cohesive weekly plan for an automatic controller. This directly addresses the learning outcome: Develop a complete irrigation schedule for an automatic controller.
By the end of this lesson, you will be able to:
- Determine the optimal watering days and frequency for each zone.
- Assign zones to controller programs based on plant and hardware type.
- Implement "cycle and soak" settings to prevent runoff and improve water absorption.
- Create a final, organized schedule chart that is ready to be programmed into a controller.
This is the last piece of planning before we produce the final project drawings and documents.
1. From Runtime to a Functional Schedule
An automatic irrigation controller doesn't just know "run for 33 minutes." It needs to be told when and how. A complete schedule defines three key elements for each group of zones (or "Program"):
- Watering Days: Which days of the week should the system run? (e.g., Mondays and Thursdays).
- Start Time: At what time of day does the program begin? (e.g., 5:00 AM).
- Station Runtimes: How long does each station (zone) in that program run? (e.g., Station 1 for 33 mins, Station 2 for 15 mins).
Here is a standard chart that professionals use to organize this information. This is what we will be creating today for our project.
2. Building the Schedule: A Step-by-Step Approach
Creating a schedule is a methodical process. We'll use a comprehensive guide to walk through the necessary calculations. This guide introduces a formal, engineering-based approach to scheduling that moves beyond simple estimation.
Turf and Landscape Irrigation Scheduling
The 'Turf and Landscape Irrigation Scheduling' guide from the Irrigation Industry Association of British Columbia provides the foundational formulas for creating a robust irrigation schedule. We will focus on Part 1, which outlines how to calculate a 'Base Irrigation Schedule'.
Please read the following sections to understand the core scheduling calculations: Section 1.3 SOIL PROPERTIES (pages 10-14): Review the definitions of 'Soil Infiltration Rate' (I) and 'Maximum Soil Water Deficit' (MSWD) (N). Understanding these soil limits is key to scheduling. Section 1.4 IRRIGATION SYSTEM PARAMETERS (pages 15-18): Familiarize yourself with 'Application Rate' (O) and 'Operating Time' (R). We calculated these in the last lesson, but it's good to see them in this context. Section 1.5 SCHEDULING REQUIREMENTS (pages 18-19): This is the most critical part. Study the formulas for 'Irrigation Days (ID)' (T), 'Total Run Time per Day (Td)' (V), 'Maximum Runtime per Cycle (RC)' (W), and 'Cycles per Day (C)' (X). Example 3 (page 21): Carefully review this worked example. It brings all the previous formulas together to create a complete schedule for a turf zone from scratch.
After studying the guide, you'll see the process involves four main calculations to define the schedule for each zone. Let's break them down.
Step 1: How Often to Water? (Irrigation Frequency)
Instead of watering a little bit every day, we want to water deeply and less frequently. The guide shows us how to calculate the ideal number of watering days per week.
From section 1.5, the formula is:
- ETL for the period: This is the total water the plant needs over a week (e.g.,
5 mm/day × 7 days = 35 mm/week). - MSWD: This is the "water reservoir" in your soil's root zone that you are willing to let the plant use up before you refill it. For a lawn in loam soil, this might be around 10-15 mm.
Example (Lawn Zone):
- ETL = 35 mm/week
- MSWD = 15 mm
ID = 35 mm / 15 mm = 2.33
We always round up to avoid stressing the plants, so we would water 3 days per week. A good schedule would be Monday, Wednesday, and Friday.
Step 2: How Long to Water on Those Days? (Total Runtime per Day)
In the last lesson, we calculated the total weekly runtime. Now we just divide that by our number of watering days.
From section 1.5, the formula is:
Example (Lawn Zone):
- Our total weekly runtime was
11 minutes/day × 7 days = 77 minutes. - We are watering 3 days per week.
Td = 77 minutes / 3 days ≈ 26 minutes per watering day.
So, the schedule is now: Run for 26 minutes on Monday, Wednesday, and Friday.
Step 3: How to Prevent Runoff? (Cycle and Soak)
What if your soil can't absorb water for 26 minutes straight without runoff? This is common with clay soils or on slopes. The solution is Cycle and Soak: you break the total runtime into smaller "cycles" with "soak" periods in between.
The guide gives us the formula to calculate the maximum single runtime a soil can handle:
Example (Lawn Zone):
- Let's say our lawn is on clay soil, with an infiltration rate of about 7 mm/hr.
- Our sprinkler zone has an Application Rate (PR) of 27 mm/hr.
RC = (7 mm/hr / 27 mm/hr) × 60 ≈ 15 minutes.
This means we should not run the zone for more than 15 minutes at a time. Since our Total Runtime per Day (Td) is 26 minutes, we need to split it. The number of cycles is:
We round up to 2 cycles.
The final schedule for this zone is: Run for 13 minutes, wait for 30-60 minutes, then run for another 13 minutes. Most modern controllers have an automatic "Cycle and Soak" or "Intelligent Watering" feature that handles this for you.
Step 4: Grouping Zones into Programs
The final step is to organize your zones into programs on the controller.
Golden Rules for Programming:
- Group Similar Zones: Put zones with similar plant types and sprinkler types onto the same program. For example:
- Program A: All lawn sprinkler zones. They have similar watering day needs.
- Program B: All shrub and flower drip zones. They may need watering more frequently than the lawn.
- One Start Time per Program: A program only needs one start time. The controller will automatically run all stations in that program sequentially. If Station 1 has a runtime of 15 minutes and Station 2 has a runtime of 20 minutes, the total program will run for 35 minutes.
- Water in the Early Morning: The best time to water is between 4:00 AM and 8:00 AM. This minimizes water loss from wind and evaporation and reduces the risk of fungal diseases that can occur with evening watering.
- Respect Hydraulic Limits: Ensure the total flow rate of zones running at the same time does not exceed your available water supply flow rate. Since controllers run zones sequentially, this is rarely an issue unless you have multiple controllers or programs starting simultaneously.
Our Villa Project Schedule
Let's apply these principles to create the schedule for our 600 m² villa project. We have three zones:
- Station 1: Lawn (Sprinklers)
- Station 2: Shrubs (Drip Line)
- Station 3: Planter Boxes (Drip)
| Parameter | Station 1 (Lawn) | Station 2 (Shrubs) | Station 3 (Planters) |
|---|---|---|---|
| Watering Needs | 5 mm/day, deep/infrequent watering preferred | 3 mm/day, consistent moisture preferred | 6 mm/day, requires frequent water |
| Weekly Runtime | ~77 minutes | ~189 minutes (27 min/day) | ~315 minutes (45 min/day) |
| Irrigation Type | Sprinklers (High PR) | Drip (Low PR) | Drip (Low PR) |
| Soil/Slope | Loam soil, slight slope (potential for runoff) | Mulched beds, flat | Potting mix, excellent drainage |
| Calculated Frequency | 3 days/week | 5 days/week | Daily |
| Daily Runtime | 26 mins | ~38 mins | 45 mins |
| Cycle/Soak Needed? | Yes (e.g., 2 cycles of 13 mins) | No | No |
Based on this, here is a logical schedule:
Program A: Lawn Sprinklers
- Stations: Station 1
- Watering Days: Monday, Thursday, Saturday
- Start Time: 5:00 AM
- Station 1 Runtime: 26 minutes (with Cycle and Soak enabled on the controller)
Program B: Drip Zones
- Stations: Station 2, Station 3
- Watering Days: Every day
- Start Time: 4:00 AM (can run before the sprinklers, as drip is silent)
- Station 2 Runtime: 27 minutes (we'll stick to the daily calculation from last lesson)
- Station 3 Runtime: 45 minutes
Test your understanding!
Why did we put the Drip zones on a separate program (Program B) from the Sprinkler zone (Program A), instead of running them all under one program?
Show answer
There are two main reasons:
- Different Watering Frequencies: The lawn sprinklers need to run 3 days a week, while the drip zones (especially the planters) need water daily. Controller programs are designed to apply the same frequency (watering days) to all stations within them.
- Different Irrigation Types: It's a best practice to separate sprinklers and drip. This allows you to adjust schedules independently. For example, in a cooler month, you might reduce the lawn watering days but keep the planter box watering daily.
Conclusion
Congratulations! You have now mastered the final analytical step in irrigation design: creating a complete, efficient, and horticulturally sound watering schedule. You can translate raw data about plants, soil, and hardware into a set of precise instructions for an automatic controller.
Key Takeaways:
- A controller schedule consists of Watering Days, Start Times, and Station Runtimes.
- Watering frequency (
Irrigation Days) is determined by the plant's water needs (ETL) and the soil's water holding capacity (MSWD). - Cycle and Soak is a critical technique to prevent runoff when the sprinkler application rate exceeds the soil's infiltration rate.
- Logically grouping zones into Programs based on plant type and hardware is essential for flexible and efficient scheduling.
In our next and final lesson, we will consolidate all our work. You will produce the two key deliverables for your capstone project: the fully annotated Irrigation Plan and the complete Bill of Quantities (BOQ).