Individual Lot Drainage/Grading Plan And Floodplain Compensatory Storage Areas

Lot drainage refers to the finished grade of individual lots being shown on the construction plans. Generally, lots shall be graded in accordance with Types A, B, or C typical grading plans as shown in the images below. Construction outside of Special Flood Hazard Areas (SFHA) may still require a drainage plan. A drainage plan addresses lot grading and stormwater runoff from a rainstorm, while the SFHAs refer to a 1% annual chance flood event.

Typical Lot Grading Type ‘A’

Figure 1: Typical Lot Grading Type ‘A’
Typical Lot Grading Type ‘B’

Figure 2: Typical Lot Grading Type ‘B’
Typical Lot Grading Type ‘C’

Figure 3: Typical Lot Grading Type ‘C’

A drainage plan should include, at a minimum:

  • The proposed Finished Floor Elevation (FFE) of the structure
  • Existing ground elevations in the area(s) of construction
  • Proposed ground elevations in the area(s) of construction
  • The intended drainage path (flow arrows and/or elevations) to ensure no adverse impact on adjacent or off-site properties.
  • Flood zone delineation line (if applicable)
  • Wetland delineation line and buffer line (if applicable)
  • Signed and sealed by a Florida registered Professional Engineer
Sample drainage plan
Figure 4: Sample drainage plan

Floodplain Compensatory Storage:

The floodplain provides a valuable function by storing floodwaters. When fill or buildings are placed in the flood fringe, the flood storage areas are lost and flood heights will go up because there is less room for the floodwaters. This is particularly important in smaller watersheds which respond sooner to changes in the topography.

Pasco County requires cup for cup compensatory storage to offset any loss of flood storage capacity. If your project proposes fill in the floodplain, the drainage plan will need to show the volume of fill to be added to the floodplain and the volume to be removed to demonstrate zero net encroachment. Refer to section 902.2.G.5 of the land development code.

Illustration of floodplain compensatory storage area

Figure 5: Illustration of floodplain compensatory storage area