§ 138-3662. Low impact development (LID) landscaping.

Low impact development (LID) is an ecologically-based stormwater management approach favoring soft engineering to manage rainfall on site through a vegetated treatment network. The goal of LID is to sustain a site's pre-development hydrologic regime by using techniques that infiltrate, filter, store, and evaporate stormwater runoff close to its source. Contrary to conventional "pipe-and-pond" conveyance infrastructure that channels runoff elsewhere through pipes, catchment basins, and curbs and gutters, LID remediates polluted runoff through a network of distributed treatment landscapes. The use of LID shall be implemented in conjunction with the Pinellas County Stormwater Manual.

The toolbox of LID-integrated management practices, including structural and nonstructural designs, is most effective when applied in a treatment train, or series of complementary stormwater management practices and techniques. Typically, LID practices will not completely replace more conventional "bottom-of-the-hill" stormwater management practices, but can be used to complement these practices and to ensure that the entire stormwater management system meets the Pinellas County water resources objectives. LID practices are optional and may be incorporated to landscaping areas.

(a)

LID planting zones.

Surface grade and ponding area of a bio-retention structure are the first factors to consider when choosing which plants to specify. Stormwater planters and some rain gardens have uniform surface grades. In these designs, ponding will be equal across the structure and all plants will have the same conditions (Zone A). In bio-retention swales and some rain gardens, soil surface is sloped, resulting in differing planting conditions across the structure (Zones A and B). Plants located at the bottom where ponding occurs, will have different requirements than those placed on the sideslopes, which receive runoff, but not ponding. A third planting area may occur outside of Zones A and B, on the upper edges of rain gardens and bioswales (see Figure 138-3662.a). This area is not a functional component of the bio-retention area, and therefore can be treated as a traditional landscape area.

Figure 138-3662.a Planting Zones

(b)

LID plant species selection.

Once the plant zones are identified (Zone A only or both Zone A and Zone B) for a structure, the plants may be selected. Plant selection should take into account the following factors;

(1)

Tolerance of varied moisture conditions (wet and dry);

(2)

Tolerance of varied soil types and growing conditions;

(3)

Availability in Central Florida plant nurseries;

(4)

Low maintenance requirements;

(5)

Are not invasive weeds;

(6)

Do not have aggressive/invasive root systems; and

(7)

Exhibit an attractive appearance.

When selecting plants, additional site-specific information, such as tolerance to high and low temperatures, coastal conditions and prevailing winds should be considered. In addition, project specific aspects of the design, for example right-of-way vegetation height limits, may further influence selection. Pinellas County Stormwater Management Manual includes acceptable LID options.

(Ord. No. 18-36 , § 3(Att. B), 10-23-18)