City of Lincoln Downtown Irrigation Management Plan
Executive Summary
The 2019 Downtown Irrigation Management Plan is a strategic plan to improve and maintain the City of Lincoln’s greater downtown irrigation system over the next five to 10 years.
This plan identifies the observations made about the greater system and defines implementable strategies and priorities for an efficient irrigation system to support Lincoln’s vibrant and colorful downtown.
The study area was confined to all city-owned irrigation systems and corresponding landscaping areas within downtown, generally defined by Pinnacle Arena Drive to 21st Street and Lincoln Mall to S Street.
Irrigation
There are several types of irrigation equipment used in the study area:
- Spray Heads
Rotors
On-surface drip irrigation
Sub-surface drip irrigation
Spray Head Irrigation
Spray heads are sprinklers that provide a steady spray of water over an area, typically a turf area. They are installed below ground with the sprinkler head out of sight while inactive. Once the sprinkler system is activated, a small portion of the head will rise above the surface, typically four to six inches, to disperse water.
Rotor Irrigation
Rotors are similar to spray heads, providing a steady stream of water, but the spray rotates and covers broader open turf areas. The area covered by rotors evaluated in this study area ranged from 25 to 50 feet.
On-Surface Drip Irrigation
A dripper line is polyethylene tubing that releases water through emitters, or small holes, spaced at various intervals onto the landscape. The lines should be laid out in a pattern of parallel lines 18” apart and stapled every three feet with stainless steel staples approximately 6” long.
On-surface dripper lines are the best method of irrigating planting beds.
Sub-surface Drip Irrigation
Sub-surface drip irrigation was installed in the recently redeveloped areas in the Haymarket and around Pinnacle Bank Arena.
Lack of irrigation
Non-irrigated Areas
There are many landscape beds in the downtown Lincoln area that are not irrigated, or irrigation has been halted because of construction, a water line/valve break, the system has not been turned on, or has never been irrigated. These beds show little to no plant life.
Minimal plant life observed at 10th and Q streets
Irrigation System Components
In addition to irrigation type, system inventory assessed the following components:
- Controller/Timers
- Wire Connections
- Meters
Controller/Timers
An irrigation controller, sometimes referred to as timer, refers to how an irrigation control zone is operated. Controllers can be manual, automatic, or remotely controlled. There were two types of controllers identified as part of this evaluation: battery-operated and two-wire systems.
Controller Box
Wire Connections
Wire connections provide power to the irrigation equipment. The wire connections need to be waterproof .
Pressure Regulation and Filtration
Pressure regulation is necessary with dripper lines for two reasons: (1) dripper lines have fittings that do not need clamps if the pressure is 45 psi or below and (2) dripper lines work best at 15 psi to 45 psi.
Filtration is necessary with dripper lines because of the small openings in the emitters. Without filtration, the emitters become clogged with debris and fail to work. Poor or no filtration will limit the lifetime of the drip system. Filtering needs to be 120 mesh or greater.
Spray Heads
Spray head irrigation was properly placed throughout the turf areas but in many areas the heads should be adjusted to achieve an even flow.
Spray heads used in densely planted landscape beds were often blocked or deflected, causing over-watering to some plants and lack of water to others.
The map to the right differentiates the areas irrigated with spray heads that are in proper working order from those in need of adjustment.
Irrigation and Landscape Rating
In addition to being geo-located, the irrigation system and landscape areas were evaluated and assigned an overall qualitative ranking from 1 (lowest quality) to 5 (highest quality). The purpose of the rating system was to help facilitate recommendations towards prioritizing efforts to restore or newly construct the downtown irrigation.
IRRIGATION SYSTEM RATING CRITERIA
Score of 1 (Lowest)
- Dripper lines not stapled
- Incorrect wire nuts, not direct bury
- No filtration
- Dripper lines were not spaced correctly, 18”
- Spray heads were used to irrigate a planting bed
Score of 2
- Dripper lines not stapled
- Correct direct bury wire nuts
- No filtration
- Dripper lines were not spaced correctly, 18”
Score of 3
- Dripper lines stapled
- Correct direct bury wire nuts
- No filtration
- Correct pressure regulation
- Dripper lines were not spaced correctly, 18"
Score of 4
- Dripper lines stapled
- Correct direct bury wire nuts
- Correct pressure regulation and filtration
- Dripper lines were not spaced correctly, 18”
Score of 5 (Highest)
- Dripper lines stapled
- Correct direct bury wire nuts
- Correct pressure regulation and filtration
- Dripper lines spaced at 18”
- Irrigation heads were level and adjusted correctly
LANDSCAPE AREA RATING CRITERIA
Score of 1 (Lowest)
- Planting area was devoid of plant material or all remaining plant material was dead or significantly declining in place.
- Soil compaction was so severe that probing with soil knife trowel met refusal within the top 1” to 2” of the soil profile.
- Soil organic material was minimal to not present.
- Turf lawn locations demonstrating large percentage of bare soil, large dead turf patches, and significant to exclusive creeping weed cover in conjunction with significant soil compaction.
Example of landscape rating of 1
Score of 2
- Planting area has significant loss of plant material with remaining plant material visually sustaining or in lower degree of visual stress and decline.
- Soil compaction is significant with soil probing meeting resistance in reaching full depth of sampling.
- Organic material is present but only within the lower range of the top 0-4” of the soil profile
- Tree pits within sidewalks where mature sized trees are present that have significantly small bed size (3’ x 3’ cut outs in walk observed), trees are restricted to growing within raised planter (16th Street M to N), or tree roots have grown over or have heaved the sidewalk (N Street, 16th to 17th Streets). Tree however remains in a sustaining growth habit with full leafed out canopy.
Example of landscape rating of 2
Score of 3
- Plant material present is predominantly viable with limited patches of decline or dead plant material.
- Soil composition varied from moderate to significant compaction within samplings of same bed
- Organic material was present and at least to a 4” depth. Organic material consisted of topsoil or natural mulch decomposition.
- Turfgrass areas were predominantly green with a limited level of browning or creeping weed presence, typically in areas with longer plant area history (east of 10th to 17th Streets) but considered adequate for vegetative cover within an urban area.
Example of landscape rating of 3
Score of 4
- Plant material was consistently viable and in positive growth. Minimal to no sign of stress to plant material.
- Soil compaction moderate with no encounter of significant compaction.
- Organic material was present at least 4” depth or greater and clearly consisted of topsoil beyond solely decomposed mulch.
- Overall planting area conditions found to be in very good to excellent condition and desired structure for long-term landscape sustainability.
Example of landscape rating of 4
Score of 5 (Highest)
- Planting area consists of all criteria of a score of 4.
- Soil compaction was found to be low and slightly better than compaction found in a ‘4’ planting area.
- Soil organic material was present within full probe sample depth or deeper and consisted of rich topsoil with suggested enhancement of compost and/or sand amendments. These planting areas found primarily within new and recently constructed landscape areas (West Haymarket, N Street bicycle median, P Street, bioretention basins).
- Overall planting area viewed as near optimum expectation from method of construction, bed preparation, and plant material vibrancy.
Example of landscape rating of 5
IRRIGATION RATING SUMMARY
Through the evaluation effort, it was evident the older, more established downtown areas demonstrated greater signs of irrigation system degradation. Newer more efficient systems, primarily in the Haymarket and Pinnacle Bank Area, follow today’s industry best practices.
Today’s development trends involve incorporating more green spaces for landscaping and outdoor activity. As a result of this trend, when the irrigation asset ratings are normalized for area covered, the newer areas of redevelopment within the downtown area skew the ratings overall to the higher end of the rating scale
LANDSCAPE RATING SUMMARY
Following similar observations as the irrigation ratings, more established downtown areas demonstrate greater signs of landscape degradation. Younger landscape beds follow today’s industry best practices for soil preparation. The beds likely have nutrients and are more suitable for plant life success. This trend extends to the southern edges of downtown, again mostly reflecting private development or public infrastructure projects.
While the more recently touched areas of downtown have the higher rated landscaping scores, the landscape beds are in good condition. When the landscape bed ratings are normalized for area covered, the vast majority of beds are at or above average
ACTION PLAN
The more recently redeveloped areas of downtown have irrigation and landscapes systems in good condition, however there are expansive areas that require immediate attention to follow industry best practices. An action plan was developed as a framework to implement the necessary improvements. There are two action item categories: (1) near-term improvements or (2) long-term management.
NEAR-TERM IMPROVEMENTS
Near-term improvements should be addressed immediately and completed by the end of 2022:
- Ensure all wire connectors are weatherproof.
- Replace spray head irrigation in planting beds with on-surface dripper lines.
- Add filtration to the dripper control zone valve in all existing dripper line irrigated planting beds.
- Verify best management techniques were used in all beds that have been converted to on-surface dripper lines.
- Fix non-functional beds.
LONG-TERM MANAGEMENT
Long-term management action items can be implemented concurrently with the near-term improvements but will require intentional workload planning and adequate funding over the next five years:
- DLA to designate landscape water manager.
- Implement adaptive management practices.
- Continue tracking improvements in current GIS form, work with city Information Technology (IT) to integrate into a city-wide asset management system and develop a digital work-ticket process.
- Convert battery-operated controllers to either a cellular-based controller (Weathermatic S-Reach) or if a two-wire is in place, a two-wire decoder (Rain Bird ESP-LXD).
- Over time upgrade each irrigation bed to a two-wire system and Rain Bird ESP-LXD controller, to be compatible with the Rain Bird IQ central control system.
- Conduct systematic irrigation audit to determine scheduling coefficient (SC) and other areas for potential improvements.
Existing vs. Optimal Irrigation by Corridor
The cost estimate for each corridor follows the methodology listed above to implement irrigation industry best management practices. The below interactive map illustrates the difference between the irrigation system as it exists today, and the optimal irrigation system, once the near-term improvements have been implemented.
Operations Dashboard for ArcGIS
