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Permit Review Detail
Review Status: Completed
Review Details: FLOODPLAIN
Permit Number - T21OT00467
Review Name: FLOODPLAIN
Review Status: Completed
| Review Date | Reviewer's Name | Type of Review | Description | Status | Comments |
|---|---|---|---|---|---|
| 07/27/2021 | JOHN VAN WINKLE | ENGINEERING | REVIEW | Reqs Change | T21OT00467 1) Page 4, Section 1.3. Recent updates, adopted by the City have eliminated non-designated basins. As such any previously non-designated basins are considered balanced. 2) Page 56, Section 6 - On-Site Soil Characteristics. Please clarify how only 1 boring location, approximately 1200' away from the proposed substation is sufficient to provide geo-technical evidence of the soil conditions used to support a reduction in the erosion hazard setback (EHS). As noted on page 7 "The site was also previously used as an inert landfill and subsurface conditions are unknown". Please submit a sealed geotechnical report specific to this project that provides soils information at a minimum from the end of the existing southern bank protection (shown in Figure 33) to distance beyond the northern extents of the project outside of the EHS. The report should be sufficient, if needed, to construct bank protection and support any proposed operations and maintenance plan 3) Ensure the proposed EHS's are consistent throughout the presentation. The delineations on page 9 of 84 and on page 83 of 84 are slightly different. 4) Tucson Code Sec.26-2: In report, please provide additional discussion as well as delineations on plan views that depict EHS according to the following comments: a. The setback for the Santa Cruz River regional watercourse is measured from the top edge of the highest channel bank or edge of the base flood water surface elevation, whichever is closer to the channel center line. b. Provide discussion in the report regarding compliance with this section of the code since it appears that the rc / Tw ratio indicates that the criteria is not met to use the straight section setback; EHS per code would be 1,230 feet. c. Clarify, label and delineate EHS per Tucson Code Sec.26-7.1 on plan views that include both current code EHS and proposed project's EHS on plan views that show EHS. d. The 200-foot proposed EHS appears arbitrary as no calculation was provided to show how the number was determined. Please provide how the setback was derived. 5) Tucson Code Sec. 26-11.2(f): Regarding page 9, a revised layout should be considered to address the following comments: a. Relocation of the interceptor swale to flow counter-clockwise around proposed fill pad was offered in a previous meeting and might provide area to shift the proposed TEP infrastructure further northwest. b. Showing minimum 2-feet offset at property boundaries for cut or fill slopes shall be included in the planview. c. Show minimum access width requirements on planview around proposed infrastructure. d. TEP substation layout may need to minimize footprint area to meet City erosion hazard setback safety requirements. e. Detention / Retention waiver can be included in Development Package submittal, with provision for first flush. Typically, the request for waiver, or the request and documentation with response from PDSD Engineering or Floodplain Administration, is placed within the drainage report for the first submittal. Keep in mind that first flush requirement may still be required by PDSD Engineering. f. Explain where any 500-year floodplain exists on the parcel and how proposed Critical Facility meets requirements for utility features such as generators or other machinery that will need to be elevated above the 500-year floodplain per Tucson Floodplain ordinance freeboard requirements. Critical Facility requirements for utility features such as generators or other machinery will need elevation above the 500-year floodplain. 6) Tucson Code Sec. 26-11.2(f): Engineering and safety concerns include: a. Future meandering is unknown. Although the location of the end of the west bank soil cement has a curve in the alignment that can lessen flow velocities if the east bank does not change alignment, at the same time, the soil cement alignment also directs floodwaters toward the subject parcel. b. The potential danger exists if the parcel erodes during a storm event and onsite substation materials is swept onto other lands or downstream to cause injury to others, and blockages and diversion of floodwaters within the regional watercourse. c. Consideration of project's impact to the existing closed City of Tucson Ryland Landfill located on opposite side of bank of the Santa Cruz River. If sufficient EHS is not provided there is a potential to create a danger or hazard to life or property in the area, or result in increased flood hazards or additional threats to public safety if the substation fails to function from the impact of an erosion hazard. d. Technical Stnd Sec.4-04.7.5: Existing bank soil conditions using data from sieve analysis and Figure 8 of the report indicates an allowable velocity of less than 2.5 fps yet report indicates slightly higher velocities at west embankment exist, making the west bank vulnerable to the erosion hazard. e. Historical information indicates this section of the regional watercourse has meandered back and forth across the TEP property. f. Unknown fill material at the subject property may or may not increase future erosion potential. Previous uses of the site for sand and gravel pit activities may have changed consistency of soil compaction and may increase potential for erosion risk. g. Per exhibit on page 55 of the report (page 23 of appendix D), during the 1983 flood event higher velocities were seen west of the eastern thalweg, which indicates some proclivity to meander back toward the TEP property. 7) Tucson Code Sec.26-2: If a variance is to be proposed, keep in mind that the City of Tucson mayor and council requires that the any proposal for a variance be exceptional, unusual, and peculiar to the property involved. Mere economic or financial hardship alone is not exceptional. Inconvenience or physical constraints, cannot, as a rule, qualify as an exceptional hardship. All of these problems can be resolved through other means without granting a variance, even if the alternative is more expensive, or requires the property owner to build elsewhere or put the parcel to a different use than originally intended. 8) Tucson Code Sec.26-12(c)(1)a: Applicant may submit a request for a variance however the submittal shall include a concise explanation of all matters in dispute and any pertinent maps, drawings, data or other information in support of the appeal. 9) Tucson Code Sec.26-7.1: The City recently adopted more restrictive erosion hazard setback requirements for the regional watercourse since the chances for flood and erosion disaster would more likely occur along the regional watercourses. City of Tucson Floodplain Administration carefully reviews any proposed projects adjacent to the regional watercourses to avoid future loss of life and property and requires compliance to the erosion hazard setbacks as provided in the Flood and Erosion Hazard Management Code. An acceptable protection improvement for the proposed critical facility would provide 100-year protection that extends from existing soil cement located upstream of parcel at approximately 400 feet south of subject parcel and extend beyond downstream side of parcel with a key-in at a distance from top of bank at floodway that would equate to the 100-year EHS, and would include appropriate toe down to scour depth. 10) If a Variance request is made and relies on an operations and maintenance plan, that plan must clearly identify at a minimum a. The measures that will be taken should erosion occur that would threaten the facility b. A boundary line, which if crossed would trigger improvements. Since The proposal indicates that a 500 year event migration would be approximately 250', but proposes a set back of 200', the mitigation efforts likely extend off site c. The land or area needed to mitigate and agreements or easements as needed with the City of Tucson and Pima County Flood Control for the use of that land d. A funding source for any mitigation or improvements 11) Please review section 26-12 of the Tucson City code, which outlines the variance process John Van Winkle, P.E. John.VanWinkle@tucsonaz.gov |
| 07/27/2021 | JVWINKL1 | DOT ENGINEERING | REVIEW | Completed | please refer to engineering comments |
Final Status
| Task End Date | Reviewer's Name | Type of Review | Description |
|---|---|---|---|
| 11/12/2021 | DBENOIT1 | APPROVAL SHELF | Completed |
| 11/12/2021 | DBENOIT1 | OUT TO CUSTOMER | Completed |
| 11/12/2021 | DBENOIT1 | REJECT SHELF | Completed |