Engineering Updates


January 4, 2018


The following amendments are proposed to the Drainage and Erosion Control Design Manual (DCM) to address frequent review comments, maintenance issues and clarify design criteria to improve the development process. Staff considers the proposed amendments to the DCM necessary to protect the public health, safety and welfare, and adhere to standard engineering practice. The amendments also clarify drainage infrastructure requirements to assist in the development review process. They will be presented to Planning Commission on January 9, 2018 for a recommendation to City Council and presented to City Council on January 22, 2018 for approval.


Section 2.3 – Clarify and revise channel definition, design frequency and freeboard requirements.


Freeboard requirements are specified in Section 2.3.Freeboard is the factor of safety above a design flood level to compensate for many unknown factors that could contribute to stormwater heights greater than the height calculated. Design frequency and minimum freeboard for drainage facilities, including channels and creek improvements, are provided in Table 2-2. Footnote and definition text in the DCM has led to uncertainty on the freeboard requirements for channels; therefore, staff is proposing to clarify and revise definitions, design frequency and minimum freeboard requirements.


The channel drainage facility is proposed to be separated from creek improvements and swale and ditches removed. Channels with drainage areas greater than 128 acres shall meet the current requirement of a 100-year storm event plus 1 foot of freeboard. Channels with drainage areas less than or equal to 128 acres shall be designed to contain the 100-year storm event or 25-year storm event plus minimum freeboard, whichever is greater.


Sections 2.10.2 and 8.1 – Clarify easement and maintenance access criteria.


Access to channels is critical for maintenance, inspection and repair. The DCM provides the following criteria on easement and maintenance access:


  • Maintenance access shall be provided for all channels and have a width of 12 feet and a cross slope no greater than 2 percent.
  • Easement width shall be the width of the 100-year water surface and a clear width of 14 feet, minimum, shall be included for access.


The Platting Ordinance also states that easements along open channels shall provide sufficient width for the channel and such additional width for maintenance equipment.


Staff is proposing to clarify the requirements by specifying that easements for channels shall extend 2 feet on one side and 12 feet on the other side for maintenance access. Easements that parallel and adjoin a roadway shall extend out 2 feet on both sides of the channel. That clarification supports the current requirements and will include figures. Additionally, it is proposed that maintenance access shall be provided at a minimum spacing of one access at 1,000 foot intervals and that the bottom of the channel cannot be considered for maintenance access.


Section 8.1 – Specify when a concrete pilot channel is required.


Staff is proposing to specify that a 4 foot, minimum, concrete pilot channel is required for a channel when the longitudinal slope is less than 0.5 percent and when the bottom width of a channel is greater than 30 feet. This generally follows standard practice and City of San Antonio requirements, and address anticipated maintenance issues based on existing cases.


Section 8.1 – Specify when fencing is required for concrete channels.


Staff is proposing to specify that a 42 inch, minimum, fence or rail be required adjacent to a concrete channel where vertical walls exceed 2 feet and where side slopes exceed 2:1 and the depth is greater than 2 feet.


December 27, 2017



The City of New Braunfels Engineering Division would like to provide the following updates related to engineering standards and development.


1.                  Curb Ramp Standards. The curb ramp standards have been updated to include ramp placement and new detectable warning surface details. Detectable warning pavers are no longer permitted without the approval by the Public Works Department due to ongoing construction and maintenance issues. The updated standard is located at http://nbtexas.org/281/Details-Standards.We will continue to use this standard in conjunction with City of San Antonio’s Wheelchair Ramp Standards.


 


2.                  Drainage and Erosion Control Manual.Updates were approved by city council on August 28, 2017 to Section 2, Drainage Policy and Criteria in the Drainage and Erosion Control Manual (DCM) to implement best practices and address community needs. The updated DCM is located at http://nbtexas.org/280/Drainage-Manual-Ordinance-Forms-Maps. Key updates include the following:


a.       Specified requirements for preliminary and master drainage plan reports.


b.       Specified the elevation of the lowest floor elevation above finished grade and stormwater conveyance structures.


c.       Require lot grading plan at plat and building permit.


d.       Specified that changes in runoff characteristic that create point discharge(s) or any increase in discharge rates or velocities require outfall into right-of-way or drainage easement that has capacity and verification of no adverse impact.


e.       Specified that engineered walls greater than three feet shall be designed to prevent freefall of stormwater.


f.       Specified pumped drainage facilities requirements.


 


3.                  Platting Ordinance Streets Design Standards. Amendments were approved by city council on September 11, 2017 to Chapter 118, Platting, Article IV, Design Standards, Section 118-46 Streets to implement current practice and address inconsistencies. Key updates include the following:


a.       Section 118-46 (l) Landscaped islands and traffic calming


                                                              i.     Redefined “landscape islands” to “medians” and specified traffic function and sight distance requirements.


                                                            ii.     Removed traffic calming design information including figures, listed acceptable traffic calming options and specified design to meet established standards.


b.       Section 118-46 (s) Pavement and right-of-way width, street grades and horizontal curves for public streets


                                                              i.     Addressed inconsistencies between ordinance text, approved thoroughfare plan and engineering street sections.


                                                            ii.     Removed street section figures and specified street information in the text.


                                                          iii.     Specified minimum grade and updated minimum centerline radius requirements.


                                                          iv.     Referenced AASHTO and TxDOT design requirements.


c.       Section 118-46 (y) Trafficimpact analysis


                                                              i.     Amended text to be consistent with Chapter 114.


                                                            ii.     Removed TIA worksheet from the code to allow for staff updates as needed.


d.       Section 118-46 (z) Street signs


                                                              i.     Specified that the developer is responsible for all street signs in the city and extraterritorial jurisdiction with approved construction plans.


 


4.                  Traffic Impact Analysis Worksheet. The Traffic Impact Analysis (TIA) Worksheet has been updated to allow for tracking multiphase developments and provide information and conformance with previously approved TIAs and mitigation measures. The updated TIA Worksheet is located at http://nbtexas.org/280/Drainage-Manual-Ordinance-Forms-Maps.


 


5.                  Drainage Report and Public Infrastructure Construction Plans Requirements. Amendments were approved by city council on September 11, 2017 to Chapter 118, Platting, Article III, General Platting Procedures to properly plan for development and address community concerns on development impacts. The amendments shall take effect for all master plans, plats and planned developments filed with formal application after January 1, 2018.The formal application deadline for the February 6, 2018 Planning Commission meeting is December 27, 2017. After January 1, 2018, the following will be required in conjunction with requirements in Chapter 118:


a.       Subdivision Master Plan. Master drainage plan report including drainage site plan, existing watershed map, preliminary drainage site plan and master drainage plan summary. Report requirements are specified in the DCM.


b.       Preliminary Plat. Preliminary drainage report including preliminary drainage site plan and conformance with the master drainage plan report. Report requirements are specified in the DCM. If there are no drainage improvements or changes with the plat, the owner shall submit a letter with the application indicating as such.


c.       Final Plat. An application for a final plat shall be accompanied by a letter of approval from the city engineer and/or the public works director approving the public infrastructure improvement construction plans showing details of streets, alleys, culverts, bridges, storm sewers, water mains, sanitary sewers and other engineering details of the proposed subdivision. Approval of public infrastructure improvement plans is required prior to final plat application. If there are no public improvements or changes with the final plat, the owner shall submit a letter with the application indicating as such.


d.       Planned Development. Master drainage plan report including drainage site plan, existing watershed map, preliminary drainage site plan and master drainage plan summary. Report requirements are specified in the DCM.


e.       If a final plat application is submitted without approved public infrastructure improvement plans as required by ordinance, the applicant will be notified and given the option to submit as a preliminary plat.


 


6.                  Drainage and Erosion Control Manual Proposed Channel Revisions. City staff will be presenting proposed revisions to channel requirements to planning commission on January 9, 2018 followed by approval by city council. The revisions include revising and clarifying channel freeboard requirements, adding fencing requirements for concrete channels with vertical walls greater than two feet, and clarifying channel access requirements. The proposed revisions will be posted prior to the meeting on the webpage below and presented at the meeting.


 


7.                  Engineering Updates. City staff is working on other items to improve engineering standards, process and review. This includes information on water quality requirements and a new streets design guide. Future updates to these and other items will be provided at http://nbtexas.org/2145/Engineering-Updates.Feel free to contact us at engineering@nbtexas.org if you have any questions or would like to verify city engineering requirements.