Parameter and criteria considerations -- Documentation of parameter and criteria considerations includes data source identification, evaluation of data, assessments of the reliability of data, what decisions were made and why, qualifying statements such as limitations and disclaimers, and design values comprising the set of parameters and criteria that govern the design. Design parameters define the limits of the facility design. For example, in sizing a structure, design parameters include economically available shapes, environmentally suitable materials, and physical geometric limitations. Examples of criteria include allowable headwater (for a culvert), allowable through-bridge velocity (for a bridge), and maximum allowable water discharge rate from a pump station. Both design parameters and criteria are established from the unique characteristics of the design site and situation. The parameter and criteria considerations should be fully documented for the design of TxDOT drainage facilities.

Federal and state regulatory criteria (see ).

TxDOT procedures and practices (see ).

Past performance of existing facilities at the subject location. Such experience may include operation during flood events, erosion activity, structural response to flood events, failures, maintenance required (and for what reason), and description and cost of maintenance. District offices should develop and maintain systematic documentation files of facility experiences either at the district or at the local level.

Judgments, assumptions and decisions incorporated in the decision process or design.

Plan, profile and detail drawings explaining the design.

Special Provisions, Special Specifications, or General Notes governing material and construction requirements for any element of the drainage design not addressed by standard specifications.