TM 5-820-11AFM 88-5, Chap. 1
SURFACE DRAINAGE FACILITIES FOR
AIRFIELDS AND H E L l P O R T S
1. Purpose and scope. This manual prescribes standards of design of surface drainage of airfields and
Problems involved in the design of drainage facilities are discussed, and convenient methods of
design capacities are outlined. These standards can be altered when necessary to meet special
or unusual conditions on the basis of good engineering practice. Design of drainage facilities
or subarctic regions is discussed in TM 5-852-7/AFM 88-19, Chap. 7 (see app A for referenced
2. Design objectives for airfield and heliport surface drainage. Surface drainage facilities will be
designed to suit the mission and the importance of airfields or heliports; the design capacity will be
adequate to accomplish the following objectives:
a. Surface runoff from the design s term. Surface runoff from the selected design storm will be
disposed of without damage to the airfield facilities or significant interruption of normal traffic.
b. Surface runoff from storms exceeding the design storm. Surface runoff from storm exceeding the
design storm will be disposed of with minimum damage to the airfield facilities and with the shortest
practicable interruption of normal traffic. The primary runway will remain operational under all
c. Reliability of operation. The drainage system will provide maximum practicable reliability of
operation under all climatic conditions.
d. Maintenance. The drainage system in the immediate vicinity of operational facilities will require
e. Coordination. Basic data obtained during preliminary field investigations will be coordinated with
the facility master plan and with other agencies having jurisdiction over conservation, flood control,
drainage, and irrigation.
f. Safety requirement. Separate drainage and containment should be provided in areas with a high
potential for fuel spills. This provision will allow spilled fuel to be promptly separated, collected, and
removed from the rest of the drainage system.
g. Future expansion. Drainage design should allow for future expansion with a minimum of expense
and traffic interruption.
h. Environmental impact. Drainage facilities will be constructed with minimal impact on the
3. Drainage protection required.
a. Degree of drainage protection. The degree of drainage protection depends largely on the
importance of the airfield or heliport, the mission and volume of traffic to be accommodated, and the
necessity for uninterrupted service. Within certain limits the degree of drainage protection should be
sufficient so that hazards can be avoided during operation.
b. Frequency of the design storm. Drainage for military airfields and heliports will be based on a
2-year design frequency, unless exceptional circumstances require greater protection. Temporary pending
will be permitted on graded areas adjacent to runway and taxiway aprons, or airfield or heliport
pavements other than primary runways. Pending will not be permitted on primary runways under any
condition. To determine the extent of pending permissible on areas where pending is allowed, possible
damage of pavement subgrades and base courses as a result of occasional flooding must be considered.
In addition, pending basins must conform to grading standards.
4. Hydrologic considerations.
a. Definitions. The following definitions are used in the development of hydrologic concepts.
(1) Design frequency. The average frequency with which the design event, rainfall or runoff, is
equaled or exceeded. The reciprocal of frequency is the annual probability of occurrence. Design
frequency is selected to afford the degree of protection deemed necessary. Except in special
circumstances, the 2-year frequency, that is, an annual probability y of occurrence of 0.5, is considered
satisfactory for most airfields.
(2) Design storm. The standard rainfall intensity-frequency relation, lasting for various durations
of supply. The design storm is used to compute the runoff to be carried in drainage facilities.
(3) Rainfall-excess. The amount of rainfall which appears as surface runoff. Rainfall-excess is
rainfall less losses to infiltration or other abstractions.