Summary of Hydraulic Calculations



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DRGC-East Breakout

Summary of Hydraulic Calculations




Summertime Drive


There are two breakouts along the east side of the Las Vegas Wash into Summertime Drive (Wash Cross Sections 1125 and 1124). At the southeast end of Summertime Drive, elevated land along a powerline easement forces this runoff back into the Las Vegas Wash.

Section 1118 Weir


At the approximate location of the Las Vegas Wash Cross-Section 1118 within Ballinger Drive there is a sump. 929 cfs approaches the sump from the north: Eastwick Circle and Ballinger Drive. 362 cfs drains directly to the sump from the Las Vegas Wash (Section 1119). 165 cfs breaks out to Ballinger Street from the Las Vegas Wash (Section 1118) and drains back to the sump from the south.
It is assumed that once the flow reaches the sump area, that it does not weir back into the Las Vegas Wash. The total flow of 1,456 cfs can weir out at three separate places.


  1. An easement directly to the east

  2. South on Ballinger Drive.

  3. East on Longbow Drive.

An AutoCAD quick section was drawn at each of the three possible outlets. An approximate elevation of 1729.07 must be achieved before the 1,456 cfs flows out to the three outlets.




  • 169 cfs goes east in the easement between the rows of houses

  • 440 cfs goes east in Longbow Drive

  • 847 cfs goes southeast in Ballinger Drive



Labrador Drive Weir


169 cfs is conveyed east to Labrador Drive. AutoCAD quick sections were drawn in the easement on the opposite side of Labrador Drive and within Labrador Drive south of the easement. Weir calculations show that 169 cfs will overtop the two weirs at an approximate elevation of 1728.21.
The results show 157 cfs in Labrador and the remaining 12 cfs continues east in the easement. Since the depth of flow in the 80-foot wide easement is less than 1-foot, it was conservatively assumed that the entire flow (169 cfs) continues south in Labrador Drive.

Forsythe Drive


At the Longbow Drive intersection, approximately 100 feet south of the easement, the 169 cfs combines with the 440 cfs (described above) and continues south to Forsythe Drive.
The flows continues east in Forsythe Drive to a T-intersection at Crowley Drive. The runoff can either

An attached weir calculation shows 295 cfs passing between the houses. That 295 cfs is then used as the starting flow in the Sloan Lane HECRAS Model.


The entire flow of 609 cfs is also conservatively assumed to head south in Crowley to the Ballinger intersection.


Ballinger Drive


From the Section 1118 Weir calculation, 847 cfs travels south in Ballinger Drive. There is a series of breakouts along the east side of the Las Vegas Wash as it parallels Ballinger Drive.


Las Vegas Wash Breakout Summary

Las Vegas Wash

X Section



Breakout flow

(cfs)


1117

157

1116

229

1115

129

The total flow of 1,362 cfs continues east in Ballinger Drive. Lateral Weirs at Brassy and Bowstring were used to quantify flows that leave Ballinger (used as starting flows in the Brassy & Bowstring HECRAS Models respectively).


At the Ballinger/Crowley intersection, we have 880 approaching from the west and 609 cfs approaching from the north. Valley gutters direct flows to the south. A highpoint exists in Ballinger east of the intersection. Multiple iterations were conducted to balance the weir flow depth (flow that continues east in Ballinger) and the EGL of the section just south of the intersection. We concluded that 566 cfs flows east from Ballinger into Sloan. The remaining 923 cfs continues south in Crowley.
At the Slice/Crowley intersection, we have 923 cfs approaching from the north and 776 cfs approaching from the west. An AutoCAD quicksection along the highpoint at the east and south sides of the development was drawn. A weir calculation was performed to determine at what depth the total flow of 1699 cfs will weir out of the development between the houses and at Slice Drive (WSE = 1718.24).
Therefore runoff approaching from the north and west (Slice/Crowley intersection) will pond to a depth of 1718.24 before the entire 100-year storm event can outlet to surrounding areas. This water surface elevation (1718.24 was used as the boundary condition for the Ballinger and Brassy HECRAS Models.

Brassy Drive


A lateral weir in the Ballinger HECRAS model shows that 197 cfs turns south in Brassy Drive. There is a series of breakouts along the east side of the Las Vegas Wash as it parallels Brassy Drive. A final total flow of 491 cfs turns east in Slice Drive at the southern end of Brassy Drive.
At the Bowstring Drive intersection, an additional 285 cfs is added to the flow in Slice Drive. The resulting flow (776 cfs) recombines with the Ballinger flow at the Slice/Crowley intersection.
The weir depth along Crowley (and by implication, the ponding depth at the Crowley/Slice intersection) is used as the boundary condition for the Brassy HECRAS Model.

Bowstring Drive


A lateral weir in the Ballinger HECRAS model shows that 285 cfs turns south in Bowstring Drive.
The upstream water surface elevation in Brassy Drive (Section 4448), at the Bowstring intersection was used as the boundary condition for the HECRAS Model.

TerraSanta Apartments


At Section 1106 of the Las Vegas Wash HECRAS Model, we have 522 cfs breaking out of the wash into the TerraSanta Apartments. This 522 cfs will travel southeast through the parking lot (normal depth flow > 1.0 feet). It is assumed that nothing leaves the apartment complex at the entrance drive. The total 522 cfs continues toward the southeast corner of the apartment complex.
At Section 1105 of the Las Vegas Wash HECRAS Model, we have 410 cfs breaking out of the wash into the TerraSanta Apartments. This flow will follow a swale along the south side of the apartment complex. Since the flow is not contained in the HECRAS model for this area, the model is not included, and the apartment complex is included in the floodplain. The depth of flow along the property block wall is approximately 2.5 feet. It is assumed that the flow remains within the apartment complex.
At the SE corner of the apartment complex the 410 cfs combines with the 522 cfs. Since it is unlikely that the entire 932 cfs passes through the drainage easement, half is assumed to continue to Roundrock Drive and the other half breaks out through the electrical substation to Sloan.

Roundrock Drive


At Section 1104 of the Las Vegas Wash HECRAS Model, we have 670 cfs breaking out of the wash into the residential neighborhood at the north end of Raywood Street. This flow is assumed to split equally: half flows east in Roundrock, half flows south in Raywood.
About halfway along Roundrock, 466 cfs from the TerraSanta apartment is added to the 335 cfs already in Roundrock.
The flows continues southeast in Roundrock Drive to a T-intersection at Springstone Street. The runoff can either

  • continue east, passing over highpoints between the houses and then into the Sloan Lane ROW, or

  • turn right and head south in Springstone.

An attached weir calculation shows 119 cfs passing between the houses. The remaining 682 continues south in Springstone to the Ruby Creek intersection.



Ruby Creek Drive


As mentioned previously, we have 335 cfs at the north end of Raywood Street.

There is a series of breakouts along the east side of the Las Vegas Wash as it parallels Raywood Street and Ruby Creek Drive.



Las Vegas Wash Breakout Summary

Las Vegas Wash

X Section



Breakout flow

(cfs)


1103

515

1099

4

1098

81

1097

141

1096

33

1095

189

1094

336

1093

163


Since the flow in the roadway is so great for a 50-foot ROW, it is assumed that the entire area is underwater and is therefore included in the floodplain. This roadway was not modeled.

Sloan Lane


Starting flow – 295 cfs from weir flow between houses at east end of Forsythe.

Add 566 cfs at Ballinger intersection.


As the flow continues south, the breakout flows from the Crowley/Slice weir is added to Sloan. Since the 295 cfs flow from the Forsythe weir is double counted (assumed to go into Sloan and also assumed to head south in Crowly), the Crowley/Slice weir flows were normalized (reduced by 295 cfs).
A lateral weir was originally put in the Sloan HECRAS Model at Commodore Cove. Since the breakout flow was less than 10 cfs, the weir was removed from the model and the entire flow was assumed to remain in Sloan.
A second lateral weir was put in the Sloan HECRAS Model at Woodfield Drive. 161 cfs leaves the model and continues east. At the eastern end of Woodfield Drive this 161 cfs is assumed to enter the Sloan Channel, which ultimately returns the flow to the Las Vegas Wash.
A third lateral weir was put in the Sloan HECRAS Model at Sahara Avenue. 203 cfs leaves the model and continues east to the Sloan Channel, which ultimately returns the flow to the Las Vegas Wash. An additional 104 cfs enters the model from breakouts at the apartment complex west of Sloan (north of Sahara). Therefore the flow in Sloan, south of Sahara is 2006 cfs.
Since the depth of flow in Sloan is greater than 1-foot, the block wall along the electrical substation is ignored. Ineffective flow areas are still included due to the increased width of flow. An undeveloped parcel at the southeast corner of Sloan and Sahara is almost 1-foot lower than Sloan Lane. Flows along the eastern edge of the parcel are at least 2-feet up on the perimeter block wall. A lateral weir has 877 cfs breaking out into the adjacent neighborhood east of Sloan.
Three east/west streets east of Sloan are separated by a block wall. The depth of flow in Sloan is at least 1-foot high on this wall at Windy Point Trail, Rainbow Bridge Drive, and Glory Canyon Way and therefore lateral weirs were placed at those three locations.
With all of the breakouts along Sloan Lane, the final flow at the south end of Sloan is 1013 cfs plus an additional 2,479 cfs from Ruby Creek Drive. A final weir along the east side of Sloan and the Las Vegas Wash determines the final disposition of this 3,501 cfs.


  • 1,805 cfs drains directly into the Wash

  • The remaining 1696 cfs drains into the neighborhood east of Sloan – 211 cfs in Mahogany Mountain and 1485 cfs breaking through the houses along Morning Break Court. (Note that 1,578 cfs was already in this neighborhood from previous breakouts.)


Sunrise Meadows (Housing development SE of Sahara and Sloan)


Flows from Sloan Lane breakout into the Sunrise Meadows development as it travels south toward the Las Vegas Wash.
877 cfs enters the development at the undeveloped parcel at the corner of Sahara and Sloan. The 877 cfs is assumed to flow south in Oak Meadow. With a longitudinal slope of 0.4 percent, the normal depth in the street is 2.6 feet (Flowmaster Section SM1).
An additional 346 cfs breaks out of Sloan at Windy Point Trail. It joins the flow in Oak Meadow, giving a total flow of 1223 cfs. The 1223 cfs is assumed to flow south in Oak Meadow. With a longitudinal slope of 0.4 percent, the normal depth in the street is 3.14 feet (Flowmaster Section SM2).
An additional 225 cfs breaks out of Sloan at Rainbow Bridge and it joins the flow in Oak Meadow, giving a total flow of 1448 cfs. The 1448 cfs is assumed to flow south in Oak Meadow. With a longitudinal slope of 0.4 percent, the normal depth in the street is 3.46 feet (Flowmaster Section SM3).
An additional 130 cfs breaks out of Sloan at Glory Canyon and it joins the flow in Oak Meadow, giving a total flow of 1578 cfs. The 1578 cfs is assumed to flow south in Oak Meadow. With a longitudinal slope of 0.55 percent, the normal depth in the street is 3.32 feet (Flowmaster Section OM1).
The 1578 cfs in Oak Meadow combines with 221 cfs that breaks out of Sloan at Mahogany Mountain Drive at a low point in Mahogany Mountain Drive. A weir calculation along Mahogany Mountain Drive shows that the total flow 1789 cfs will pond to a water surface elevation of 1707.9 before it all weirs over into the streets south of Mahogany Mountain Drive.

1001 cfs will flow south in Sunrise Day Court

521 cfs will flow south in Windy Breeze Court

267 cfs will flow south in Mossy Oaks Lane

1789 cfs total flow in Mahogany Mountain Drive


The four north/south streets south of Mahogany Mountain Drive (Morning Break Court, Sunrise Day Court, Windy Breeze Court, and Mossy Oaks Lane) slope to the south. The bank along Las Vegas Wash is elevated, forcing flows to the east. Weir calculations at the south end of each of these streets were conducted to quantify the dispensation of these breakout flows.

Morning Break Court


1485 cfs breaks out of Sloan through the houses along the west side of Morning Break Court. The runoff ponds to an elevation of 1708.16. At that water surface elevation, 820 cfs reenters the Las Vegas Wash and the remaining 665 cfs overtops the highpoint at the southeast end of the street and flows into Sunrise Day Court.

Sunrise Day Court


The 665 cfs from Morning Break Court combines with the 1001 cfs coming from Mahogany Mountain Drive. The total flow of 1666 cfs ponds to an elevation of 1706.84. At that water surface elevation, 1095 cfs reenters the Las Vegas Wash and the remaining 571 cfs overtops the highpoint at the southeast end of the street and flows into Windy Breeze Court.

Windy Breeze Court


The 571 cfs from Sunrise Day Court combines with the 521 cfs coming from Mahogany Mountain Drive. The total flow of 1092 cfs ponds to an elevation of 1706.32. At that water surface elevation, 925 cfs reenters the Las Vegas Wash and the remaining 167 cfs overtops the highpoint at the southeast end of the street and flows into Mossy Oaks Lane.

Mossy Oaks Lane


The 167 cfs from Windy Breeze Court combines with the 267 cfs coming from Mahogany Mountain Drive. The total flow of 434 cfs ponds to an elevation of 1705.15. At that water surface elevation, 428 cfs reenters the Las Vegas Wash and the remaining 6 cfs overtops the highpoint at the southeast end of the street and flows into Mahogany Forest Court.
For convenience, the 6 cfs is assumed to reenter Las Vegas Wash

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