1      PROJECT BACKGROUND

The focus of the project is the natural wash and the sediment basin adjacent to the Arrowhead Lakes Development.    The area to be studied is at the Thunderbird Park located in the City of Glendale near 59th Avenue south of Pinnacle Peak road.  The natural wash flows south through the park into the sediment basin.  The sediment basin is connected to the Arrowhead Lakes through a weir.  There is also a recirculation of some flows from the Arrowhead Lakes into the sediment basin.  In addition, there is some effluent discharged into the sediment basin.  The purpose of the study is to delineate the inundation boundaries of the natural wash for the 2, 10, 50 and 100 year flood events and establish the nature of the basin with respect to sediment trapping.

2   DATA COLLECTION

Data collection was performed to review existing hydrology and hydraulics.  The hydrology information was obtained from the Glendale-Peoria Area Master Plan Update Reports by Entellus, Inc.  The report contains a volume that addresses the Arrowhead Lakes Hydrology.  This volume of the reports provided the HEC-1 model for the area of interest.  This HEC-1 model is part of a larger HEC-1 model developed by that study.  The watershed boundary for the region is shown in Appendix A as presented in the Glendale-Peoria Area Master Plan Update Reports.   

A field visit was conducted to determine the existing conditions.  Photographs taken during the field visit are presented in Appendix B.  The field visit showed the presence of sandy channel bottom in most wash with dense vegetation in the downstream most section upstream of 59th Avenue. 

The topography information was provided by Logan Simpson Design Inc. 

The as-builts for the sedimentation basin were obtained from the City of Glendale.

3      HYDROLOGY

The existing hydrology was obtained from the Glendale-Peoria Area Master Plan Update Reports by Entellus Inc.  The HEC-1 model obtained from that report contained the hydrologic model for the 100-year 24-hour storm event.  For the purpose of the this study, this model was modified to obtain the hydrology for the 2yr, 10yr, 50yr and the 100yr events.  This was performed by using the data in the PREFRE portion of the model within DDMSW software.  The peak flows obtained from the hydrology models are presented in Table 1.

Table 1  Peak Flows

4     HYDRAULIC ANALYSIS

The hydraulic analysis was performed using the HEC-RAS (Version 3.1.2) software by US Army Corps of Engineers.  The topography information provided by Logan Simpson Design was used to provide the cross-section geometries.  ArcGIS software and GEORAS extension were used to generate the cross-section geometries.   

The Manning’s n values were set based on the observations during the field visit.  A value of 0.03 was used for the sandy channels and 0.045 was used for the overbanks.  A value of 0.035 was used in the downstream portion where more dense vegetation was observed.   

The field visit revealed the presence of a box culvert at 59th Avenue and 2 RCP culverts at road crossings inside the Thunderbird Park.  These culverts were modeled by using approximate dimensions observed during the field visit.

The peak flows presented in Table 1 were used as the flow data in the HEC-RAS model.  A normal depth boundary condition was used at the downstream boundary.   

The model results are presented in Appendix C. 

5      FLOODPLAIN DELINEATIONS

The water surface elevations from the results presented in Appendix C were used to generate the flood inundation boundaries for the 2, 10, 50 and 100 year flow events.  The delineations are approximate and are presented in Appendix D.  The delineations indicate a breakout for larger flows in the upstream portion of the reach located north of Thunderbird Park and south of Pinnacle Peak road.  The presence of a small ridge contains the larger flows and directs the flow into the natural wash as flows move south. The presence of the berm in the south side downstream portion of the reach (upstream of 59th Avenue) contains flow in that side of the reach.  The flows are directed under the box culvert into the basin located east of the 59th Avenue.  

6      SEDIMENTATION BASIN

The as-builts of the basin located in the region northeast to the intersection of 59th Avenue and Melinda Drive were obtained from the City of Glendale.  The asbuilts shows that the basin is, in fact, designed and built as a sedimentation basin.  The as-builts also indicate that the effluents are discharged in this basin from the near-by wastewater treatment plant. 

7      SUMMARY

The existing hydrology for the natural wash located between the Pinnacle Peak Road and the 59th Avenue was reviewed.  The existing HEC-1 model was used to obtain the 2, 5, 10, 50 and 100 year peak flows.  A field visit was conducted to document the existing conditions.  A hydraulic model was developed and floodplain boundaries are delineated.  Documentation related to the basin located adjacent to the 59th Avenue were reviewed and it was determined that basin was designed to act as a sedimentation basin in addition to other purposes.

8      ACKNOWLEDGEMENTS

JE Fuller/Hydrology & Geomorphology, Inc. would like to thank Entellus Inc. for providing access to the Glendale-Peoria Area Master Plan Update Reports.

9      REFERENCES

Entellus Inc., “Glendale-Peoria Area Master Plan Update Reports,” Prepared for the Flood Control District of Maricopa County, 1991. 

Hydrologic Engineering Center, “HEC-RAS River Analysis System,” Hydraulic Reference, U.S. Army Corps of Engineers. 

Hydrologic Engineering Center, “HEC-RAS River Analysis System,” User’s Manual, U.S. Army Corps of Engineers.

APPENDICES

APPENDIX A
      WATERSHED DELINEATION 1
      WATERSHED DELINEATION 2

APPENDIX B
      FIELD VISIT PHOTOGRAPHS

APPENDIX C
      HEC-RAS HYDRAULIC MODEL RESULTS

APPENDIX D
      FLOODPLAIN DELINEATIONS