10 Watershed Technical Memo.pdf — original pdf

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TECHNICAL MEMORANDUM TO: FROM: Mr. Bradford Massingill III Resident at 110 Red Bird Lane Williamson Creek Watershed J. Eduardo Perez, E.I.T., C.F.M. Watershed Protection Department September 25, 2023 DATE: SUBJECT: Drainage Pattern and Public Infrastructure around Your Property The purpose of this memorandum is to document the drainage pattern and the public infrastructure affecting the drainage pattern near your property. Your address 110 RED BIRD LN is near S Congress Ave and E Stassney Ln, and in the Williamson Creek watershed. The drainage pattern of any creek ecology is affected by qualities in the landscape such as ground surface slope and type of ground cover. When rain falls water collects in territorial low spots and eventually, once enough water has ponded in these spots, water pours ‘downstream,’ in strict accordance to laws of physics. Streams wash over natural terrain via creeks, channels, and streambeds eroding landscapes into gravel and clay. The earthen material, once eaten away by washing water, is deposited elsewhere as silt and mud, molding landscapes and natural terrains. The size of this effect can be witnessed in person or can be captured via satellite imagery. The drainage assets that affect the drainage pattern near your home are summarized in the The awesome behavior of running water is consistent, dynamic, ecological, and economic. For these reasons, the City of Austin Watershed Protection Department keeps track of drainage assets that allow for these phenomena to occur in a harmonious and comprehensible manner for the residents of Austin. Map titled: WPD Map of Drainage Assets near 110 Red Bird Lane. 110 Red Bird Ln. Three Types of Infrastructure to Convey Rainfall Runoff BACKGROUND Drainage data and other calculations are provided in the Table: Drainage Summary for Concept Designs for engineered drainage infrastructure are provided in Appendix A: J. Eduardo Perez EIT, CFM and Kathy Rock visited the address 110 RED BIRD LN as a continuation of a flood investigation in this block of Red Bird Lane. The group witnessed what Mr. Massingill had experienced with the lack of storm-drain infrastructure between the north and south lots of Red Bird Lane. Preliminary drainage calculations showed a large drainage area, and a quick inventory of WPD drainage assets yielded no results. E. Perez called Mr. Massingill after visiting the site address to confirm field investigation discoveries. After speaking with Mr. Massingill, I (J. E. Perez) took to initiative to author this technical memo to summarize my findings. METHODOLOGY The City of Austin Drainage Criteria Manual references the Rational Method as an acceptable method of calculating storm runoff resulting from precipitation events i.e. rain. Section 2 of the City of Austin Design Criteria Manual describes the equations and methodology used to calculate the proceeding hydraulic flow estimates. For brevity, no portion of that text will be shared here. CALCULATION SAMPLE Q10 = C * Intensity * Area = 0.85 * 9.6 in/hr * 5.9 acres * (1cfs/1.0083in-ac/hr) = 47 cfs FIGURES Table 1 and 2 – Drainage Summary for 110 Red Bird Ln Z:\4_N_thru_R\Red_Bird_Ln_110\RedBirdDrainage_techmemo.docx 2  Figure 1 – WPD Map of Drainage Assets near 110 Red Bird Lane Appendix A – Three Types of Infrastructure to Convey Rainfall Runoff • Concept 1: Trapezoidal Channel at 0.8% – 20ft Wide - Dimensions Shown  • Concept 2: Rectangular Concrete Channel @ 1.5% and 1.0% – 10 Ft Wide – Dimensions Shown Z:\4_N_thru_R\Red_Bird_Ln_110\RedBirdDrainage_techmemo.docx 5  Z:\4_N_thru_R\Red_Bird_Ln_110\RedBirdDrainage_techmemo.docx 6  • Concept 3: 30in Reinforced Concrete Pipe (Circular) @ 1.5%– Dimensions Shown o Note: 24” RCP shown for comparison Z:\4_N_thru_R\Red_Bird_Ln_110\RedBirdDrainage_techmemo.docx 7  Z:\4_N_thru_R\Red_Bird_Ln_110\RedBirdDrainage_techmemo.docx 8  Z:\4_N_thru_R\Red_Bird_Ln_110\RedBirdDrainage_techmemo.docx 9  Z:\4_N_thru_R\Red_Bird_Ln_110\RedBirdDrainage_techmemo.docx 10