Evaluation for Local Precipitation

DOE-STD-1020-2002

hydrodynamic loads) or other effects (e.g., scour, erosion) is made on a

SSC-by-SSC basis.

For new construction locate the SSC above the DBFL, if possible. If this

cannot be done, proceed to Step 4.

Develop a design strategy to mitigate flood hazards that impact the SSC.

Options include hardening the SSC, modifying the flood path, and

developing emergency operation plans to provide for occupant safety and

to secure vulnerable areas. The flood hazard must be mitigated such that

the performance goals are met.

If the SSC is located below the DBFL level (even if the SSC has been

hardened), emergency procedures must be provided to evacuate personnel

and to secure the SSC prior to the arrival of the flood (see Step 10).

Evaluation for Local Precipitation

Develop an initial site-drainage system and roof-system drainage plan and

structural design per applicable regulations. Typical stormwater

management systems are designed for not less than the 25-year, 6-hour

storm. The minimum storm sewer size is typically 12 inches and the

minimum culvert size 15 inches. For roof drain systems, the minimum

pipe size for laterals and collectors are typically 4 inches. Stormwater

management systems usually have sufficient capacity to ensure that runoff

from the 100 year, 6 hour design storm will not exceed a depth of 0.87 feet

at any point within the street right-of-way or extend more than 0.2 feet

above the top of the curb in urban streets.

Perform a hydrological analysis for the site to evaluate the performance of

the site stormwater management system (considering roof drainage and

man-made and natural watercourses) for the DBFL local precipitation for

each SSC. The site analysis must determine the level of flooding (if any)

at each SSC. Guidelines for performing a hydrological analysis are

contained in DOE-STD-1023 and DOE-STD-1022.

For SSCs where flooding occurs, the engineer must assess whether the

performance goals are satisfied. If the SSC performance is unsatisfactory,

a modification of the site stormwater management system is required (see

Step 9). Due to the different Performance Category DBFLs, this step may

be performed for a number of flood events.

Evaluate the drainage and structural design of roof systems for the DBFL

local precipitation. The structural design of the roof system must satisfy

design criteria for loads due to ponding that result from clogged/blocked

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