Water runoff from irrigation is a major issue in New Jersey, where dense development, varied soils, and frequent storms increase the risk that excess irrigation will carry sediments, nutrients, and pollutants into storm drains, streams, and coastal waters. This article explains how to design, operate, and maintain irrigation systems to minimize runoff while keeping landscapes healthy and conserving water. It focuses on practical steps, diagnostic tests, and local considerations so property managers, landscape contractors, and homeowners in New Jersey can reduce waste and regulatory exposure.
Irrigation runoff contributes to several local problems: degraded water quality in rivers and bays, clogged storm drains, wasted potable water, and potential municipal violations where overspray or discharge reaches public storm systems. New Jersey has many MS4 municipalities and stormwater rules encouraging best management practices; even when a permit is not directly applicable, reducing irrigation runoff is both environmentally responsible and cost-effective.
New Jersey has a humid temperate climate with spring and fall as wet seasons in many areas, hot humid summers, and freezing winters. Early morning evapotranspiration is lower than mid-day rates, so scheduling is different by season. Summer thunderstorms can make rainfall unpredictable, increasing the value of weather-based or sensor-based controllers.
Soils in New Jersey range from sandy coastal plain soils with high infiltration to dense clay in parts of the Piedmont that accept water slowly. Soil texture and compaction drive how fast applied water can infiltrate. A system that works on sandy soil will likely runoff on compacted clay unless application rates are adjusted.
Sloped lawns and landscapes directly above driveways, sidewalks, or storm drains are high-risk locations for runoff. Properties near streams, wetlands, or the coast should use stricter controls and vegetated buffers to trap and infiltrate any excess water.
Group plants with similar water needs into the same irrigation zones. Separate turf, perennial beds, shrubs, and trees into distinct zones. Hydrozoning reduces overwatering of low-water-use beds and under-watering of high-use turf.
Install pressure regulators and properly sized pipes and valves so heads operate at manufacturer-recommended pressures. Excess pressure increases spray drift and decreases uniformity, causing wet spots and runoff.
On sloped sites or zones that drain downhill, install check valves or antisiphon devices to prevent low-head drainage that can saturate the downhill edge and produce continuous flow into pavement or drains.
Smart controllers that adjust schedules based on local ET (evapotranspiration) or soil moisture sensors dramatically reduce unnecessary irrigation. In New Jersey’s variable climate, these controllers prevent irrigation immediately after rain events and reduce runtime during cool cloudy periods.
Always water during early morning hours (before sunrise or shortly after) to minimize evaporation and wind drift. For sites with slow infiltration or slope, use cycle-and-soak: split run times into multiple short cycles separated by soak intervals to allow water to infiltrate rather than run off.
Example: A spray zone with a precipitation rate of 1.2 inches per hour applies 0.2 inches in 10 minutes. If the soil infiltration rate is approximately 0.3 inches per hour, run times should be short enough that applied depth per cycle is less than what the soil can absorb before starting the next cycle. Typical cycle lengths range from 5 to 15 minutes with soak intervals of 20 to 45 minutes depending on slope and soil.
Many New Jersey municipalities require or strongly encourage rain sensors and the use of flow sensors for larger systems. Rain shutoff devices stop scheduled irrigation after measurable rainfall. Flow sensors detect leaks or broken heads that can cause significant waste and runoff.
Place a line of small straight-sided containers (catch cans) across the flow path of a single irrigation zone, including both high and low spots and edges. Run the zone for a timed period, typically 10 or 15 minutes. Measure and record the depth of water in each can to the nearest 0.01 inch.
To calculate precipitation rate in inches per hour: multiply the average depth collected by 60 and divide by the run minutes. Example: average depth 0.15 inch from a 10-minute run gives 0.15 * (60 / 10) = 0.9 inches per hour.
Evaluate uniformity by comparing the lowest and highest cans. Large disparities indicate poor head spacing, mismatched nozzles, or pressure issues to be corrected.
Dig a hole 6 inches deep and 6 inches wide in the target lawn or bed and place a flat board or small jar to measure. Fill the hole with water and measure how long it takes for the water level to drop 1 inch. The infiltration rate in inches per hour equals 60 divided by the number of minutes to drop one inch. If it takes 20 minutes, infiltration is 3 inches per hour; if it takes 120 minutes, it is 0.5 inches per hour.
Use this number to schedule cycle-and-soak and to select appropriate nozzle types. If the soil infiltration is lower than the nozzle precipitation rate, split runtimes into cycles to avoid runoff.
Reducing runoff is not only about irrigation hardware. Landscape practices multiply the benefit.
While irrigation runoff is primarily an operational and design issue, be aware that many New Jersey municipalities are active on stormwater control and may require or incentivize the installation of water-efficient equipment, rain sensors, or green infrastructure. Reducing runoff supports municipal stormwater goals and can lower the risk of complaints or enforcement related to discharges to public right-of-way or waterbodies.
Reducing irrigation runoff in New Jersey is achievable with careful assessment, smart equipment choices, and disciplined scheduling. The benefits are immediate: lower water bills, healthier landscapes, and cleaner local waterways.