Chapter 6 Enginereing Sustainability: Landscape Water Conservation

Chapter 6 Enginereing Sustainability: Landscape Water Conservation#

  1. Introduction: Landscape Water conservation

  2. Simulation: Landscape Water Conservation

  3. Self-Assessment

1. Introduction#

💧 Landscape Water Conservation for Water Sustainability#

🌱 Definition and Purpose#

Landscape water conservation refers to the strategic design, management, and maintenance of outdoor spaces to minimize water use while maintaining healthy vegetation and ecosystem services. It plays a critical role in urban water sustainability, especially in regions with seasonal drought or limited freshwater resources.

🧠 Why It Matters#

  • 🌍 Outdoor irrigation accounts for 9+ billion gallons/day in the U.S.

  • 💸 Up to 50% of residential outdoor water is wasted due to poor design and maintenance

  • 🌿 Sustainable landscapes reduce runoff, improve soil health, and support biodiversity

  • 🏡 Water-efficient landscapes increase property value and reduce utility costs

🧰 EPA WaterSense Water Budget Tool#

🔎 Overview#

The WaterSense Water Budget Tool is a free, site-specific calculator developed by the U.S. EPA to help builders, landscape designers, and irrigation professionals:

  • Estimate allowable water use for landscapes

  • Design landscapes that meet WaterSense New Home Specification

  • Promote regionally appropriate plantings and irrigation systems

Reference#

[U.S. Environmental Protection Agency, 2020] helps landscape designers, builders, and irrigation professionals:

  • Estimate allowable water use for landscapes based on climate and plant types

  • Comply with Section 4.1.1 of the WaterSense New Home Specification (Version 1.2)

  • Promote regionally appropriate, water-efficient landscape design

🧮 Core Equation#

Baseline = ETo × A × Cu

🌿 Landscape Water Conservation Simulation#

📘 Overview#

This interactive model estimates monthly irrigation requirements and potential water savings for different landscape types based on:

  • 🌧️ Local rainfall

  • 🌱 Plant water needs (landscape coefficient)

  • 📏 Landscape area

It is inspired by the EPA WaterSense Water Budget Tool, which helps homeowners and planners design water-efficient landscapes.

🧮 Model Assumptions#

🔹 Reference Evapotranspiration (ET₀)#

  • Assumed constant at 150 mm/month, typical for summer in many U.S. regions.

  • Represents the water demand of a well-watered cool-season grass under standard conditions.

🔹 Landscape Coefficients (Kc)#

Landscape Type

Coefficient (Kc)

Description

Cool-season grass

0.8

High water demand

Warm-season grass

0.6

Moderate water demand

Native plants

0.4

Adapted to local climate

Drought-tolerant groundcover

0.3

Minimal irrigation required

Water need is calculated as:

\[ \text{Water Need (mm)} = ET₀ \times K_c \]

💧 Irrigation Requirement#

\[ \text{Irrigation (mm)} = \max(ET₀ \times K_c - \text{Rainfall}, 0) \]
\[ \text{Irrigation Volume (m³)} = \frac{\text{Irrigation (mm)} \times \text{Area (m²)}}{1000} \]

📊 Simulation Output#

  • Bar chart comparing rainfall contribution vs irrigation need

  • Monthly irrigation volume required for selected landscape

  • Water savings compared to cool-season grass baseline

🎛️ Interactive Controls#

  • Landscape Area: size of irrigated zone (10–1000 m²)

  • Rainfall: monthly precipitation (0–150 mm)

  • Landscape Type: choose from grass, native plants, or groundcover

📚 Use Cases#

  • Residential and commercial landscape planning

  • Water conservation education

  • Estimating irrigation costs and savings

  • Supporting LEED or WaterSense certification

🔗 Reference#

2. Simulation#

import numpy as np
import matplotlib.pyplot as plt
from ipywidgets import FloatSlider, Dropdown, IntSlider, interact

# 🌿 Landscape types and coefficients (Kc × ET adjustment)
landscape_types = {
    "Cool-season grass": 0.8,
    "Warm-season grass": 0.6,
    "Native plants": 0.4,
    "Drought-tolerant groundcover": 0.3
}

# 💧 Reference evapotranspiration (ET₀) in mm/month (typical summer value)
ET0_mm = 150

# 🌱 Main simulation function
def simulate_irrigation(area_m2, rainfall_mm, landscape_type):
    Kc = landscape_types[landscape_type]
    
    # 🌿 Landscape water requirement
    water_need_mm = ET0_mm * Kc
    irrigation_mm = max(water_need_mm - rainfall_mm, 0)
    irrigation_m3 = irrigation_mm * area_m2 / 1000  # convert mm to m³

    # 💧 Water savings compared to cool-season grass baseline
    baseline_mm = ET0_mm * landscape_types["Cool-season grass"]
    baseline_m3 = max(baseline_mm - rainfall_mm, 0) * area_m2 / 1000
    savings_m3 = baseline_m3 - irrigation_m3

    # 📊 Plot
    labels = ['Rainfall Contribution', 'Irrigation Needed']
    values = [rainfall_mm, irrigation_mm]
    plt.figure(figsize=(6, 4))
    plt.bar(labels, values, color=['skyblue', 'darkgreen'])
    plt.ylabel("Water Depth (mm)")
    plt.title(f"Irrigation Need for {landscape_type}")
    plt.tight_layout()
    plt.show()

    print(f"🌱 Landscape Type: {landscape_type}")
    print(f"📏 Area: {area_m2} m²")
    print(f"🌧️ Monthly Rainfall: {rainfall_mm} mm")
    print(f"💦 Irrigation Required: {irrigation_m3:.1f} m³/month")
    print(f"💰 Water Saved vs Cool-season Grass: {savings_m3:.1f} m³/month")

# 🎛️ Interactive controls
interact(simulate_irrigation,
         area_m2=IntSlider(value=100, min=10, max=1000, step=10, description='Landscape Area (m²)'),
         rainfall_mm=FloatSlider(value=50, min=0, max=150, step=5, description='Rainfall (mm/month)'),
         landscape_type=Dropdown(options=list(landscape_types.keys()), value="Cool-season grass", description='Landscape'));

3. Self-Assessment#

📘 Conceptual Questions#

These questions explore the physical principles and modeling logic behind the simulation.

Evapotranspiration & Crop Coefficient#

  • What does reference evapotranspiration (ET₀) represent in landscape water modeling?

  • How does the crop coefficient (Kc) modify ET₀ for different vegetation types?

  • Why is irrigation need calculated as ( \text{ET₀} \times \text{Kc} - \text{Rainfall} )?

Water Budget & Units#

  • Why is water depth (mm) converted to volume (m³) using landscape area?

  • What assumptions are made about uniform rainfall and evapotranspiration across the area?

  • How does rainfall offset irrigation demand in the model?

Sustainability Comparison#

  • Why is cool-season grass used as the baseline for water savings?

  • How do native or drought-tolerant plants reduce irrigation needs?

  • What are the trade-offs between aesthetic preferences and water efficiency?

🔍 Reflective Questions#

These questions encourage critical thinking and application to real-world landscape design and water conservation.

  • Which landscape type would be most suitable for your region’s climate and water availability?

  • How would the irrigation need change during a drought or unusually wet month?

  • What are the long-term benefits of switching to drought-tolerant groundcover?

  • How could this model be extended to include soil type, slope, or irrigation system efficiency?

  • What policy incentives could encourage homeowners to adopt low-water landscapes?

❓ Quiz Questions#

Multiple Choice#

  1. Which landscape type has the lowest crop coefficient (Kc)?
    A. Cool-season grass
    B. Warm-season grass
    C. Native plants
    D. Drought-tolerant groundcover
    Answer: D

  2. If ET₀ is 150 mm and Kc is 0.6, what is the water need before rainfall?
    A. 60 mm
    B. 90 mm
    C. 120 mm
    D. 150 mm
    Answer: B

  3. What does the irrigation volume depend on?
    A. Rainfall and landscape type only
    B. ET₀, Kc, rainfall, and area
    C. Soil moisture and slope
    D. Irrigation system type
    Answer: B

True/False#

  1. Rainfall reduces the irrigation requirement in the model.
    Answer: True

  2. Native plants require more water than cool-season grass.
    Answer: False

  3. The model assumes irrigation is needed even if rainfall exceeds water need.
    Answer: False

Short Answer#

  1. Explain how the model calculates irrigation volume in cubic meters.
    Answer: It multiplies the irrigation depth (mm) by the landscape area (m²) and divides by 1000 to convert to m³.

  2. Why might actual irrigation needs differ from the model’s estimate?
    Answer: Factors like microclimate, soil type, plant maturity, and irrigation system efficiency can affect real-world water demand.

Contents