The finished flood control design of the and its parameters are found here.
The Switzer Canyon Wash is located in Coconino County, in the northern part of the City of Flagstaff, Arizona. Flow in the wash flows from north to south, between the mountains and toward the center of the city.
Although flooding in the Switzer Canyon Wash is widespread, the area of primary concern for the project is the Hospital Hill Neighborhood area. The residents of the area along with the Elk's Lodge property owners have experienced and continue to experience flooding even with less than 1-year storm events. The purpose of this project is to develop a structure to resolve that flooding.
The attached pdf displays the project location and the proposed flood control design of the natrual channel modification and culvert bypass location.
The natural channel modification is one part of the flood control design. It is a dredging of the missing channel between Reach 1 and Reach 2. This is to help manage the floodplain in the area before the neighborhood and at Elk's Lodge. Since the water has no set path due to the missing reach, there is evidence of it spreading outwards and flooding that area. The Elk's Lodge has berms in place on the northern side to combat this flooding.
The proposed modification to this natural channel was run through software to determine its effectiveness. This can be found in the Archive. The results of this endeavor conclude that it does meet City of Flagstaff codes and the projects own standards. Construction and implementation costs are estimated to be about $750,000.
The attached pdf displays the proposed structure of the modified natural channels by reach and the average channel cross-section dimesnsions.
The culvert bypass is the other part of the flood control design. It is an implementation of an underground double-barrel culvert around the north eastern corner of the Hospital Hill neighborhood, starting at the end of Reach 3. This is to combat road flooding during storm events as between Reach and Reach 4, the water is currently expected to flow across the road into the neighborhood. There currently exists no structure that encourages the water flood that direction so there is evidence of that runoff water pooling at the end of Reach 3. Some large boulders are in place along the north eastern part of Fir Ave to reduce stormwater run-off.
The proposed double-barrel culvert model was run through software to determine its effectiveness. This can be found in the Archive. The results of this endeavor conclude that it does meet City of Flagstaff codes and the projects own standards. Construction and implementation costs are estimated to be about $4.7 million.
The attached pdf displays the design of the proposed double barrel culvert bypass.
Overall, the proposed flood control design of the natural channel modification and culvert bypass is viable in both construction and cost. The model suggests that the structure can withhold and also reduce the existing 800cfs run-off the floodplain currently receives. However, additional research should be conducted in relation to the soil quality of the site as that is not within the scope of the project. Knowing how well the foundation will function is vital to the success of this project. Excluding this additional work maintenance costs, the total project implementation is estimated to be around $5.5 million.
All additional information can be found in the Final Report.