3.5 Landscape Irrigation
The goal of roadside landscape irrigation is to allow the plants to become established such that supplemental irrigation is no longer required. TxDOT is mandated to adopt water-wise techniques associated with landscape developments per federal and state codes. In particular, rules regarding landscape irrigation in the State of Texas are found under
(July 23, 2020). Subchapters under
include standards for design, installation, and maintenance of landscape irrigation systems, as well as licensing requirements, backflow prevention and cross-connections, contracts, and warranties. In addition to these state codes, most local government entities (LGs) across the State have adopted local rules and ordinances, notably concerning water conservation practices.
Multiple methods for watering the landscape are available to achieve this goal:
- Controller-based irrigation systems;
- Bubbler and drip irrigation;
- Rainwater harvesting;
- Temporary irrigation; and
- Xeriscape irrigation design principles (see for complete list of xeriscape design principles)
To determine the best method for any given project, on-site percolation tests should be conducted to determine infiltration rates, to set minimum application rates, and to achieve a balanced irrigation design for the proposed site planting. Perform percolation tests by excavating a tree planting pit, filling the pit entirely with water and inspecting the pit within 24 hours to verify water has percolated into the surrounding soil.
3.5.1 Irrigation Systems
Controller-based irrigation systems are recommended to protect both the monetary investment in the project and to insure healthy landscape development. The design and extent of the system should be appropriate to the plant material and the location. Design and installation must meet all state and local rules and requirements related to the public water supply.
- System Design
- Irrigation components within the system should be selected for longevity and durability and should be secure from vandalism. Controllers and backflow preventers should be enclosed within lockable enclosures. All valve covers should be lockable as well. All valves and nozzles should be plastic. Typical system components are:
- Controllers may be electric, solar, two wire, and/or battery-operated;
- Rain sensors & water budgets required by state code;
- Soil moisture sensors; and
- Bubblers & drip irrigation, including laser tubing & emitters.
- If adding new irrigation to an existing system, always ensure that the components of the new system are compatible with existing equipment; controller stations, valve decoders, etc., should all work together.
- Within median and groundcover areas, drip irrigation is the best option to comply with TCEQ requirements and to avoid overspray onto pavement areas. When combined with bubblers for trees, these two components form an effective and efficient system and aid in water conservation.
- Under limited circumstances, TxDOT may consider turf irrigation within the ROW, notably in those situations where responsibility for the maintenance and operation is assumed by local governments or other TxDOT approved entities. In this case, drip irrigation is the preferred method of application.
- Inspection and Maintenance
- Main system components should be easily accessible and away from traffic lanes.
- All irrigation systems will require routine inspection and maintenance.
- In most situations, roadside landscape irrigation systems that are three to five years old will not be repaired if damaged.
- The system design should also allow for scaling back to manual operation during maintenance (when required) or during times of severe drought.
3.5.2 Temporary Irrigation
Temporary and alternative methods of irrigation vary, depending on duration of need and site accessibility. Here is some general information concerning temporary irrigation in the TxDOT ROW:
- TxDOT refers to water made available for temporary irrigation as “vegetative watering”.
- Irrigation trucks are an option for sites with access and dependable scheduling.
- Includes above ground irrigation systems that will be removed after a given time for establishment of plant material.
- Includes below ground irrigation systems that will be abandoned after a given time of establishment save for manual operation capabilities during drought years.
3.5.3 Rainwater Harvesting
Rainwater harvesting provides an alternative source to supplement or replace purchased water for irrigation. Catchment may be employed through several strategies:
- TxDOT facilities with architectural components may capture runoff from rooftops and store in above- or below-ground cisterns or collection tanks. This may be pumped as needed to irrigate the site. The TxDOT Hill County Safety Rest Area, south of Hillsboro, is an excellent example of this combination of architectural design and water conservation. An example of a rainwater harvesting system is shown in .
Figure 3-12: Rainwater Harvesting Cistern, Eastland County Safety Rest Area
3.5.4 Xeriscape Irrigation Design Principles
- Plan the irrigation system design at the same time as the planting and landscape design.
- To minimize water waste, group together plants with similar light and water requirements, and place them in an area that matches these requirements. Separate irrigation zones according to the specific watering needs of the various species of plant materials in the design.
- Use drip and/or bubbler systems for trees, shrubs, perennials, and groundcovers.
- Water deeply and infrequently to develop deep roots. Avoid watering between 10 am and 6 pm to reduce water loss through evaporation.
- Adjust irrigation controllers to accommodate changing weather/seasonal conditions. Install a rain sensor to shut off controllers when it rains.