Due to the unanticipated rapid urbanization of our once balanced urban and rural communities, storm water runoff rates and quantities have risen to unprecedented levels.

This phenomenon has instigated continued and increasing regulation by governmental agencies for permeable and vegetative solutions in erosion control.

ACB systems are comprised of a geotextile underlayment, an ACB block matrix, stone or soil aperture backfill, and (in most applications) vegetative cover.

Geotextile

The geotextile underlayment (filter fabric) serves to retain and prevent most of the subgrade soil particles from migrating through the system and being transported downstream. It is a critical element in the overall ACB design process as it must provide the system with: bidirectional water permeability, soil retention and sufficient open area for the establishment of vegetative root growth through the fabric and into the under lying soils.

The geotextile underlayment (filter fabric) serves to retain and prevent most of the subgrade soil particles from migrating through the system and being transported downstream.

ACBs

One of the many attributes of ACBs, like the Conlock system manufactured by Pavestone Company, is the finished surface?EUR??,,????'???s open area voids. ACBs exhibit open areas within and around the individual blocks that serve to provide: substructural hydrostatic pressure relief, engineered surface roughness, water permeability for ground water recharge, and open area for backfill material and the establishment of vegetation throughout the revetment lining.

Step 1. Qualify the ACB soil backfill material.

Determining the soil structure is the first step. Because of its granular structure, sandy soils will not hold on to nutrients very well. Many plant nutrients dissolve in water, so they tend to leach out of sandy soils rapidly. Clay soil has many tiny spaces that hold on to water making for generally poor drainage conditions and low oxygen levels. Clay soils will stay waterlogged after a heavy rain.

ACB blocks applied to a geotextile underlayment.

A hydroseeding layer of fine wood fiber is deposited on and around the seed to protect the seed from UV burnout and provide a medium in which water and fertilizer is suspended.

Step 2. Select the type of vegetation.

In general, you want to select a grass or plant species that is deep rooting and resistant to heavy rain and drought. The goal is to establish deep root penetration through the underlying filter fabric and into the subgrade and maintain hearty, thick and green, top foliage. Grass types are too numerous to list but here are few examples.

In general, the selected grass or plant species should be deep rooted and be resistant to heavy rain and drought.

Herbaceous species

Herbaceous vegetation, especially grasses and forbs, offers long-term aesthetics and added protection against surface (water and wind) erosion on slopes. By itself, herbaceous vegetation provides only minor protection against shallow mass movement. ACBs, combined with vegetation, minimize surface erosion.

Common bermuda has its ?EUR??,,????'??ups and downs.?EUR??,,????'?? It aggressively invades flower and shrub beds and produces a huge, uncontrollable crop of seeds. On the plus side, common bermuda will persist for decades with little care.

Hybrid bermuda is a favorite grass in warm climates because of its fine texture, good color, and ability to grow in a range of soil types. Vigorous and hardy, hybrid bermuda greens up in mid-spring and keeps its lively color until the fall frost. Hybrid bermuda becomes dormant in winter.

Bluegrass is the grass of choice in any lawn or park landscape where it is likely to grow well. Its texture and color is unsurpassed by other grasses, and is not difficult to grow if the site is a good one.

In the case of ACB brush layering, live branches or shoots of woody species are placed in the open cells of the ACBs with the stems generally oriented perpendicular to the slope contour.

Step 3. Select a starter fertilizer.

The hyphenated numbers on the front label for fertilizer stand for the major nutrients plants need ?EUR??,,????'??+ nitrogen (N), phosphorous (P), and potassium (K). The numbers, always given in the same order, represent the percentages each of N, P, and K in the bag (by weight). Other nutrients are often found in fertilizer, but not in as large amounts as N, P, and K.

Nitrogen (N) is the main nutrient for new, green growth. Plants that are almost all leaf (such as grasses) need plenty of nitrogen. When trying to establish initial growth, high nitrogen levels can be detrimental as ?EUR??,,????'??green growth?EUR??,,????'?? is not yet present. For new installations, a maximum 10% (N) should be specified (typical mid-west and northern areas?EUR??,,????'??+6%).

Phosphorous (P) promotes root development and is one of the keys to establishing hearty new grass with deep root penetration; 20 to 30% in the mix is typical.

Potassium (K) improves the overall health of plants and grasses. In typical mid-west soils, a good value for (K) in a starter fertilizer is 24.

Calcium (Ca) improves general plant health and promotes growth of young roots and shoots.

Magnesium (Mg) helps regulate uptake of other plant foods and aids in seed formation. It is also important in the dark green color of grasses and to the photosynthesis process.

Sulfur (S) helps maintain a dark green color while encouraging more rapid plant growth.

Step 4. Determine the method of application.

By far one of the best methods for applying seed grasses and plants is hydraulically seeding and mulching (also known as ?EUR??,,????'??hydroseeding?EUR??,,????'??).

The unique aspect of hydroseeding is that a layer (or blanket) of fine wood fiber is deposited on and around the seed to protect the seed from UV burnout and provide a medium in which water and fertilizer is suspended.

ACB systems incorporating vegetative linings offer an ecologically sound alternative to other conventional erosion control products. Combining the protection of hard armor and the environmental benefits of a soft, permeable cover is the biggest reason ACBs are being specified and constructed worldwide.

Herbaceous vegetation-like grasses offer long-term aesthetics and added protection against surface erosion on slopes.