North Domingo Baca Extension at Barstow

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1 Modeling Report April 5, 2001 North Domingo Baca Extension at Barstow Prepared for the Albuquerque Metropolitan Arroyo Flood Control Authority Julie Coonrod, Ph.D., P.E. Department of Civil Engineering The University of New Mexico

2 Introduction The Domingo Baca Arroyo is located in northeast Albuquerque. The transition structure in question consists of an open channel converging and discharging into a 108 diameter culvert. The 108 diameter culvert is 24 linear feet and discharges into a 96 reinforced concrete pipe running under Carmel Ave., just south of Desert Ridge Middle School. Jeff Mortensen and Associates provided a plan view, profile view, and several sectional views. Those drawings are attached to this report. The existing conditions flow rate is 538 cfs. The future conditions design flow rate is 1166 cfs. Modeling Objective The objective of this project was to build a scale model of the transition structure as shown on the provided design plans, and to use laws of similitude to determine the capacity of the structure. A further objective, which is covered in a subsequent report, is to analyze alternative designs. Designed Transition The provided design documents display plan, profiles, and sections from Station (downstream) to Station (upstream). From Stations to is an earthen transition from a natural sand bed channel to the steep concrete structure leading to a culvert. This channel has a ft/ft bottom slope, 3:1 side slopes, and a bottom width that converges to 40 feet at Station From Stations to is a concrete transition from the earthen channel to the 108-inch diameter culvert. The 108-inch diameter culvert is 24 feet long and discharges to a 96-inch culvert. The culverts do not flow under pressure. The 60-foot long concrete transition structure (Stations to 10+24) was the focus of this study. The invert of the structure drops 13 feet vertically from elevations of to The upstream 30-foot section has a bottom slope of ft/ft. The downstream 30-foot section has a vertical curve as it enters the culvert. The bottom width of the channel varies from 40 feet at Station (upstream) to 16 feet at Station to 9 feet at Station In this same section the side slopes vary from 3:1 (upstream) to vertical at Station The structure from Station to Station has vertical side walls with a 9-foot bottom width. Grout is used in the bottom corners from Station to Station (entrance to the 108-inch culvert) to transition from a rectangular bottom to a circular bottom. The 108-inch culvert does not flow under pressure. 1

3 Model Froude number similitude is required for open channel models so that the ratio of inertial and gravitational forces is the same for the model and for that which is being modeled. The pump in the lab has a capacity of approximately 2000 gallons per minute (gpm). A scale model, 1:10.8 of the actual size, was built so that the 108 diameter pipe could be modeled with a 10 diameter pipe. The corresponding future conditions design flow rate of 1166 cfs can be modeled using 1365 gpm and the existing conditions flow rate can be modeled using 630 gpm. A larger model (12 diameter pipe) would have required a model flow rate larger than the pump's capacity. Tom Escobedo, UNM Technician, and Gene Valdez, UNM Civil Engineering student, constructed the model according to the instructions given by Dr. Coonrod. The model is shown in Photos 1 and 2. Model Experiments Typically, an open channel is considered to fail when water overtops the channel edge. The model of this transition structure is somewhat unique in that under most conditions the water does not overtop the channel edge. Instead, oblique waves coming down the channel merge in the center as the transition structure steepens. The oblique waves merge with such energy that the water shoots straight up in the middle of the channel. There may be intermittent splashing outside of the channel but the water surface on the channel sides does not encroach the top of the channel. Photos 1 through 8 were taken looking downstream. The oblique waves can be seen merging at approximately Station in Photo 3. Photo 4 shows the moderate jump in the channel with an existing conditions flow rate of approximately 630 gpm (538 cfs). This moderate jump does not exceed the elevation of the sidewalls. Photos 5 through 12 show the model operating at the future conditions flow rate of 1365 gpm (1166 cfs). Under this future conditions flow rate, the height of the water in the middle of the channel exceeds the height of the channel sidewalls; however, the height of water along the sidewalls does not approach the top of the walls. Photo 12 shows the end of the model where the 10 pipe discharges back into the re-circulating tank. 2

4 The large splash can be diminished by dissipating the energy into the transition. A subsequent report reviews alternative designs for the structure. Altering the design with a splitter wall and with a cover (horizontal top wall) were investigated. One splitter wall reduces the splashing for lower flow rates. The splitter wall is shown in Photos The wall begins (upstream) at approximately Station and extends (downstream) to Station where the jump has stopped. However, as the flow rate is increased to the future conditions flow rate of 1365 gpm (1166 cfs), the splashing above the center splitter wall is similar to the splashing without the wall. Altering the open channel by placing a cover extending from Station to allows the transition structure to accommodate flow rates greater than the design flow rates. Photos 16 and 17 show the cover in place. Conclusions & Recommendations The transition structure as shown on the attached plans can accommodate both the existing conditions flow rate of 538 cfs and the future conditions flow rate of 1166 cfs. Little to no splashing is expected under the existing conditions flow rate. Under future conditions flow, intermittent splashing may occur outside of the channel; however, the channel will contain the flow. If the splashing is of concern, the channel can be converted to a culvert from stations to by the addition of a top horizontal slab. 3

5 Photo 1. Photo 4. Photo 2. Photo 5. Photo 3. Photo 6. 4

6 Photo 4. (enlarged) Note the water hitting the cross bar. Photo 5. (enlarged) 5

7 Photo 7. Photo 10. Photo 8. Photo 11. Photo 9. Photo 12. 6

8 Photo 13. Photo 16. Photo 14. Photo 17. Photo 15. 7

Domingo Baca Arroyo crossing at Jefferson

Modeling Report October 4, 2000 Domingo Baca Arroyo crossing at Jefferson Prepared for the Albuquerque Metropolitan Arroyo Flood Control Authority Julie Coonrod, Ph.D. Department of Civil Engineering The