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~ .-. • <br />Page 2 <br />Mike Savage <br />March 25, 1981 <br /> <br />4. USLE Applications: TBM has used the USLE to design sediment control <br />structures. The application is acceptable with the following exceptions: <br />LS factors for ponds 22-P7, 22-Pll, 22-PZ2, 22-P13, 22-P14, 22-P15, and 15-P15 <br />appear low from measurements made in the office. TBM must show how the LS <br />values for the areas tributary to tl~e above mentioned ponds were calculated; <br />giving slope length measurements and unit slopes. <br />5. Sediment Density: TBM has used a sediment density of 90k/ft.3 to <br />design the sediment ponds. This is a relatively high figure. TBM must <br />show how this figure was derived. <br />6. Silt Fenced Small Area Exemptions: Before the Division can evaluate the <br />areas which TBM wishes to exempt from the sediment pond requirements, TBM <br />must; give areas of the units which the exemptions will affect, describe <br />the nature of the disturbance, address the requirements of 4.05.2(3) and <br />describe installation and maintenance procedures to be followed by TBM. <br />7. Pond Design Freeboard: It is apparent from the detailed drawings <br />presented by TBM that no freeboard has been allowed in the ponds with full <br />discharge in the emergency spillways. Rs per 4.05.6(8)(d) TBM must design <br />all ponds with one foot of freeboard above the peak discharge water elevation <br />of the emergency spillways. <br />8. Pond Designed With More than 10' Spillways Bt.: From the drawings <br />supplied by TBM, most of the ponds have spillway heights of more than 10'. <br />Rs per Section 4.05.6(10) of the Regulations, TBM must present written evidence <br />of approval from the State Engineer`s Office of a letter from the SEO stating <br />that such approval is not necessary. <br />9. Required Settlement Compensation: AZI ponds must be built with 5~ more <br />height than designed to allow for settling (4.05.6[8J(eJ). <br />10. Delagua Canyon Peak Flows: In general, the concept of using adjacent <br />gauged streams to estimate peak flows for other channels is a preferred method. <br />The process requires a frequency analysis of the flow events and a close <br />correlation of watershed characteristics. Due to the short period of <br />continuous record and the disparity of watershed size, elevation range, and <br />channel sinuosity the application of this technique is unacceptable as given. <br />TBM must use another technique such as synthetic hydrograph or Peak Flows to <br />defend the culvert as i»stalled at C-4. even if the peak flow estimate as <br />generated by TBM was accepted by the Division, the culvert as installed <br />would have a design headwater of approximately 3'. TBM must revise their <br />method for culvert design as the method used by TBM is unacceptable (see 3), <br />