Description
Hydroseeding typically consists of applying a mixture of wood fibre, seeds, fertilizer, and stabilizing emulsion with hydromulch equipment, to temporarily protect exposed soils from erosion by water and wind (Figure 1). Hydroseeding is suitable for areas requiring temporary protection until permanent stabilization is established. It represents a good alternative to normal seeding or to turfing when the area interested is larger than 1000 m2, or where humans can not reach some places of the slope (by spraying through hydromulch equipment it is possible to reach great distances). They are often combined with bio-degradable geotextiles for a faster vegetation establishment and a better erosion control (BMP, 2009). However the success of this method depends on many factors including the properties and concentration of each component of the mixture, the soil characteristics, the correct choice of plant species, the prevention of seeds to be washed away from water runoff (Albaladejo Montoro et al., 2000). Hydroseeding is increasingly used as combined measure with a principal mitigation measure because of its effectiveness in restoring the area by increasing its aesthetic value (Figure 2).
Advantages
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Easiest way to establish grass on the edges, on wide slopes and other locations where the access is difficult;
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Fast installation time;
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The method can be used both for local and global slope covering.
Disadvantages
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Hydroseeding may be used alone only when there is sufficient time in the season to ensure adequate vegetation establishment and coverage to provide adequate erosion control. Otherwise, hydroseeding must be used in conjunction with mulching (i.e., straw mulch).
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Steep slopes are difficult to protect with temporary seeding;
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Not immediate erosion protection (seeds need to germinate for vegetation to be efficient against erosion);
Design methods
A preliminary evaluation of site conditions for the selection of the appropriate seed mixtures should be performed with respect to site conditions, site topography and exposure (i.e. sun/wind), vegetation type, season and climate, water availability, plans for permanent vegetation, sensitive adjacent areas.
Some basic instruction should be followed for the implementation:
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The soil to accommodate the seeds must be preliminarly prepared: scarifying the surface to eliminate crust and obstacles improves the water infiltration for the germination of the seeds.
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Hydraulic seed can be applied in single or multiple steps: in single step process seeds and mulch are applied in a hydraulic matrix. A bigger amount of seeds is required to compensate for all seeds not having direct contact with the soil. When multiple step process is adopted, a first layer of hydraulic seed is applied followed by mulch or a geotextile.
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Where seeds fail to germinate, or they germinate and die, the area must be reseeded, fertilized, and mulched within the planting season, using not less than half the original application rates;
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Irrigation systems, if applicable, should be inspected daily while in use to identify system malfunctions and line breaks. When line breaks are detected, the system must be shut down immediately and breaks repaired before the system is put back into operation;
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Irrigation systems shall be inspected for complete coverage and adjusted as needed to maintain complete coverage;
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Growing conditions vary widely across terrain suitable for hydroseeding.
Period of installation: during a season when water availability is sufficient;
Materials: seeds, fertilizers, mulch.
Functional suitability criteria
Type of movement |
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| Descriptor | Rating | Notes |
|---|---|---|
| Fall | 0 | Suitable for controlling surface erosion or slowing runoff flow along a slope/bank. |
| Topple | 1 | |
| Slide | 7 | |
| Spread | 2 | |
| Flow | 6 | |
Material type |
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| Descriptor | Rating | Notes |
|---|---|---|
| Earth | 8 | Mostly for earth and debris sediments, in some cases it can be used as additional measure for erosion protection in highly fractured rocky slopes (i.e. vegetation combined with dentition or with geonets). |
| Debris | 6 | |
| Rock | 2 | |
Depth of movement |
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| Descriptor | Rating | Notes |
|---|---|---|
| Surficial (< 0.5 m) | 9 | Vegetation is effective for controlling surface erosion. Furthermore the roots provide a reinforce for the soil, improving the slope stability at shallow depths. This technique is suitable in combination with other techniques addressing deeper slope instabilities |
| Shallow (0.5 to 3 m) | 5 | |
| Medium (3 to 8 m) | 0 | |
| Deep (8 to 15 m) | 0 | |
| Very deep (> 15 m) | 0 | |
Rate of movement |
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| Descriptor | Rating | Notes |
|---|---|---|
| Moderate to fast | 2 | Adequate for movements from extremely slow to slow, more suitable for slow and extremely slow movements (i.e. when runoff is too high the seeds still not germinated can be washed away from the soil). |
| Slow | 5 | |
| Very slow | 8 | |
| Extremely slow | 10 | |
Ground water conditions |
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| Descriptor | Rating | Notes |
|---|---|---|
| Artesian | 6 | Applicable irrespective of groundwater conditions, when enough water is available for vegetation establishment. Indirect effects on groundwater levels due to root-water uptake from plants during evapotranspiration. |
| High | 7 | |
| Low | 4 | |
| Absent | 4 | |
Surface water |
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| Descriptor | Rating | Notes |
|---|---|---|
| Rain | 8 | Mostly used for contrasting rainsplash and runoff erosion. Despite they are used along stream banks or river banks for rainwater erosion protection, they are not adequate for shoreline erosion. This technique is very useful in riverbanks as well. |
| Snowmelt | 6 | |
| Localized | 4 | |
| Stream | 1 | |
| Torrent | 2 | |
| River | 3 | |
Reliability and feasibility criteria
| Criteria | Rating | Notes |
|---|---|---|
| Reliability | 8 | Direct effect on surface erosion reduction when the vegetation is properly germinated and established. |
| Feasibility and Manageability | 10 | With the help of the proper equipment, large areas can be covered with hydroseeding in a relatively short period of time. However, the soil must be preliminary prepared |
Urgency and consequence suitability
| Criteria | Rating | Notes |
|---|---|---|
| Timeliness of implementation | 6 | Even if the implementation itself does not require too much time, the time required for the measure to become effective depends on the vegetation establishment period, which can vary depending on many factors: type of soil, availability of soil moisture, species type etc. |
| Environmental suitability | 8 | The use of indigenous species is always preferred for consistency with surrouiding environment Fertilizers used can be washed away along streambank increasing the pollution in waterbodies and threatening the fauna. |
| Economic suitability (cost) | 8 | Depending on the availability of native vegetation: costs can be addressed to mulch, supplier (for turf mats), fertilizer, equipment (for hydroseeding), site preparation |
References
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Albaladejo Montoro, J., Alvarez Rogel, J., Querejeta, J., Diaz, E., & Castillo, V. (2000). Three hydro‐seeding revegetation techniques for soil erosion control on anthropic steep slopes. Land degradation & development, 11(4), 315-325.
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California Stormwater Quality Association. Best Management Practices (BMP) (2009). Hydroseeding http://www.stancounty.com/publicworks/pdf/Development/NPDES/EC-04.pdf