Designing Efficient Hydrozones

1. The Foundation: The Landscape Plan

Every professional irrigation design begins with a detailed landscape plan. This plan is your primary source of information, dictating not just what will be planted, but where. Before any pipes are sized or sprinklers are chosen, the layout of the landscape defines the boundaries of your work.

As the video highlights, your first task is to study the plan and identify the different areas: lawn, shrub beds, trees, hardscapes, etc. These are the preliminary boundaries of your hydrozones.

2. Delineating Hydrozones on a Plan

Once you've analyzed the plant types and their Kc values (as we did in the last lesson), the next step is to draw these zones on your site plan. A hydrozone is a distinct area, containing plants with similar water needs, that will be irrigated by a single control valve.

The key steps to delineating hydrozones on your plan are:

1. Obtain a to-scale site plan. This should show property lines, the house footprint, driveways, patios, and all proposed planting areas.
2. Color-code or label plant groupings. Using the analysis from our previous lesson, mark all areas based on their assigned Kc value. For example, shade all cool-season turf (Kc=0.8) in green, all shrub beds (Kc=0.5) in blue, etc.
3. Apply the zoning rules.
   • Different Kc values? Create separate zones. A lawn (Kc=0.6) must be on a different valve than a shrub bed (Kc=0.5).
   • Mixed plantings? If a single area contains plants with different water needs (e.g., shrubs and flowers), you must either create separate zones for them or accept that you will be watering the entire area based on the plant with the highest Kc, which is inefficient.
   • Sun vs. Shade? A lawn area that is in full sun should be zoned separately from a lawn area in deep shade, even if they are the same grass type.
   • Soil or Slope Changes? Areas with significantly different soil types (e.g., sandy vs. clay) or steep slopes should be separated.

Below are two examples of what a finished hydrozone plan looks like. The first is a simple, color-coded plan, and the second is a more formal architectural drawing.

3. Calculating Hydrozone Area (m²)

With your zones clearly defined on the plan, you now need to calculate the area of each one in square meters (m²). This value is essential for determining how much water a zone requires and for subsequent hydraulic calculations.

While you are already familiar with performing area take-offs, the irregular shapes of landscape beds often require a specific approach.

The core principle is to decompose complex shapes into simple, measurable geometric forms like squares, rectangles, triangles, and circles.

Area Formulas Quick Reference:

• Rectangle: Area = Length × Width
• Triangle: Area = 0.5 × Base × Height
• Circle: Area = $\pi \times {\text{radius}}^2$ (where $\pi \approx 3.14159$)
• Trapezoid (for angled beds): Area = $(\frac{\text{Side A}+\text{Side B}}{2})\times \text{Height}$

Dealing with Irregular Curves:
For free-form shapes like kidney-bean-shaped pools or curving pathways, you can use the Offset Method.

1. Draw a straight baseline through the longest axis of the shape.
2. At regular intervals (e.g., every 1 meter), measure the width of the shape perpendicular to your baseline.
3. Average all the width measurements.
4. Multiply the average width by the length of your baseline.
   • Area $\approx$ Average Width × Baseline Length

This approximation is usually accurate enough for irrigation design.

Worked Example

Let's apply this to a simple backyard plan.

A simple site plan showing a lawn, a shrub bed, and a flower bed.

Planting Plan:

• Area A: Cool-season turfgrass.
• Area B: Mixed woody shrubs.
• Area C: Annual flowers.

Step 1: Define Hydrozones
Based on our Kc values from the previous lesson:

• Zone 1 (Shrubs): Area B. Kc = 0.5.
• Zone 2 (Lawn): Area A. Kc = 0.8.
• Zone 3 (Flowers): Area C. Kc = 0.8.
  • Note: Even though the lawn and flowers have the same Kc, the flowers will likely be irrigated with drip irrigation and the lawn with sprinklers. Different irrigation methods must be on different zones.

Step 2: Calculate Areas

• Zone 1 (Shrubs - Area B): This is a simple rectangle.

  • Area = Length × Width = 15 m × 3 m = 45 m²

• Zone 2 (Lawn - Area A): This area is a large rectangle with the flower bed (Area C) removed from it. First, we find the area of the large rectangle.

  • Total Rectangle Area = 15 m × 10 m = 150 m²
  • We need to subtract the area of the flower bed. Let's calculate that next.

• Zone 3 (Flowers - Area C): This is a semi-circle. The formula for a full circle is $\pi r^2$, so for a semi-circle it's $(\pi r^2)/2$. The diameter is 4 m, so the radius is 2 m.

  • Area = $(3.14159\times (2\text{ m}{)}^2)/2$ = $(3.14159\times 4{\text{ m}}^2)/2$ = 6.28 m²
  • We'll round this to 6.3 m²

• Final Calculation for Zone 2 (Lawn): Now we subtract the flower bed from the total rectangle.

  • Area = 150 m² - 6.3 m² = 143.7 m²

Summary of Areas:

• Zone 1 (Shrubs): 45.0 m²
• Zone 2 (Lawn): 143.7 m²
• Zone 3 (Flowers): 6.3 m²

Conclusion

You have now completed the foundational site analysis for any irrigation project. By combining the analytical skills from the last lesson with the practical drawing and calculation skills from this one, you are able to produce a clear, accurate, and defensible hydrozone plan.

Key Takeaways:

• An irrigation design starts with and is dictated by the landscape plan.
• Hydrozones are drawn directly onto the site plan based on plant type (Kc), sun exposure, soil, and irrigation method.
• Complex landscape shapes are made manageable by breaking them down into basic geometric forms (rectangles, triangles, circles) to calculate their area.
• The area (m²) of each hydrozone is a critical piece of data that you will carry forward into the next stage of design.

Next Steps

In our next lesson, we will begin Module 2 by calculating the actual water needs of our plants. You've defined the who (plant type/Kc) and the where (hydrozone area in m²). Next, you'll learn about Reference Evapotranspiration (ET₀)—the "weather" component of our equation—and use it to calculate the total daily water volume (in Liters) required for each zone.