Manual Notice: 2014-1

From: Mark A. Marek, P.E., Director, Design Division

Manual: Hydraulic Design Manual

Effective Date: May 01, 2014



Additions were made to Chapter 4 based on TxDOT research. Chapter 10 is revised; information has been updated or rearranged, and extraneous material has been removed.



Chapter 4 - Hydrology

    Anchor: #NOMFMIEI
  • Contains new information and procedures based on recent TxDOT research.
    • Section 6 - added language to clarify the statement "Structures and roadways should be serviceable (not inundated) up to the design standard."
    • Section 11 - discussion of calculation of tc in watersheds with low (flat) topographic slope
    • Section 13 - discussion of watershed subdivision and recommendations of when subdivision is appropriate
    • Section 13 - clarification of NRCS dimensionless unit hydrograph method

Chapter 5 - NFIP Design of Floodplain Encroachments & Cross Drainage Structures

Chapter 10 - Storm Drains

    Anchor: #MIMELMIE
  • The chapter has been reorganized to improve readers' comprehension.
  • Anchor: #EGJNFHMI
  • Separated equations from Section 5, Storm Drain Inlets, into a new section called Gutter and Inlet Equations.
  • Anchor: #GNQMHGLH
  • Added discussion:
    • Minimum Cover (Section 2)
    • Check Flood (Section 2)
    • Runoff from Outside Department ROW (Section 3)
    • Trench Drains (Section 5)
    • Inlet and Access Hole Energy Loss Equations (based on HEC-22) (old Section 7, new Section 8)
    Anchor: #KNPLGHKH
  • Expanded discussion:
    • Conduit Design Procedure (old Section 6, new Section 7)
    Anchor: #KJLNIGJJ
  • Condensed discussion:
    • Special Outfall Appurtenances (Section 2)
    • Design Documentation (Section 2)
    • Documentation Requirements (Section 2)
    • Hydroplaning (Section 4)
    • Slotted Drains (Section 5)
    Anchor: #HTLEHMFJ
  • Removed:
    • Vehicle Speed in Relation to Hydroplaning (Section 4)
    • Water Depth in Relation to Hydroplaning (Section 4)
    • Slotted Drain Inlet Design (Section 5)
    • Bicycle Safety for Grate Inlets on Grade (Section 5)
    • Splash Over Velocity Calculation Equations for inlet types not used by TxDOT (Section 5)
    • Splash Over Velocity Calculation Equations for metric (Section 5)
    • Manhole Spacing Criteria for metric (old Section 6)
    • Manhole Loss Equations (based on old methodology) (old Section 7)


Contact Amy Ronnfeldt at or (512) 416-2328, Roadway Design Section, Design Division with any questions or comments.



Past manual notices are available in a PDF archive.

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