Quick tips

Columns - Trends

Prevent runoff and erosion from greenhouse access roads

December 11, 2012

Julie Newman

Most growers understand the need to develop a water quality management plan to prevent pesticides and nutrients from the greenhouse and outside production areas from moving offsite. But property access roads are often overlooked despite the fact that they can cause excess runoff and erosion during storm events, leading to sedimentation that can pollute water supplies and increase flooding potential. Sediment can also carry toxic chemicals from roads offsite. Here are some tips to help you design, construct and maintain greenhouse access roads to avoid these problems.

Grade roads to minimize erosion and provide good road drainage. When designing access roads to the greenhouse, it is important to consider soil erodibilty and avoid excessive slopes. Always follow applicable grading regulations and other local and state regulations, including permit requirements. Roads should generally follow natural contours and slopes to minimize disturbance of drainage patterns; all cuts and fills should be designed to have stable slopes.

Adequate road drainage from both the road surface and hill slope is important. Waterbreaks (waterbars) — dips built at an oblique angle across the road with a berm at the end — are recommended on steep grades where runoff and erosion is anticipated. Diverted water from waterbreaks should flow only into stable areas, avoiding septic fields or waterways. Waterbreak discharge areas must be vegetated or have other erosion resistant materials. Surface crowning can also help direct road runoff into the side drainage ditches.

Protect unpaved roads from concentrated flows of water. Thoroughly compact all backfill in irrigation pipeline trenches along unpaved roads. Seed moderately used road surfaces and exposed soils with traffic-resistant vegetation, such as annual or perennial grasses, prior to the rainy season. Mulch seeded roads to protect the soil surface from rainfall impact and slow surface runoff. Mulch will also protect germinating grass seeds from drying out and prevent bird predation. Alternatively, stabilize roads with gravel. Protecting roads with vegetation or gravel is especially important if roads must be used during wet weather conditions, which aggravate erosion and drainage problems. Moreover, vegetation on sloped road banks can reduce erosion due to roots that anchor the soil. Where concentrated surface flow is a chronic erosion problem, consider providing an underground outlet drain. Consult a licensed engineer or your local Natural Resource Conservation District for proper sizing of pipe, frequency of surface riser inlets, and construction techniques.

Avoid locating roads near water bodies and waterways. If there are water bodies or waterways near the greenhouse access road, use buffers such as vegetated filter strips to protect them. Vegetated buffers are areas or strips of land maintained in permanent vegetation to prevent erosion and improve water quality by trapping and treating contaminants.

Provide on-going road maintenance to prevent runoff and erosion. Inspect culverts, roadside ditches, and outlets after each major runoff event and restore flow capacity as needed. Inspect roads with waterbreaks periodically to ensure that proper dimensions and slope are maintained and that outlets are stable. Avoid excessive road maintenance. Re-grade roads only during dry weather to remove deep ruts or damaged areas caused by storms, or to maintain proper road dimensions and slope; remove roadside vegetation that obstructs line of site or overall road maintenance. Contaminant-laden dust from traffic and wind erosion can be minimized by sealing or watering unpaved roads, ensuring that dust control with applied water does not create runoff. Minimize damage to vegetative buffers adjacent to the road when it is necessary to chemically treat the road surface.


Julie Newman is an environmental horticulture advisor at the University of California Cooperative Extension.

Have a question? You can write Julie at jpnewman@ucdavis.edu.