Lemmon Valley Estates Flood Protection
Terraphase served as the prime consultant for Federal Emergency Management Agency (FEMA) map revision and Waters of the U.S. (WOUS) delineation related to a proposed 34-acre development located southeast of the Military Road and Lemmon Drive intersection in Lemmon Valley, Nevada. The property is impacted by an unchannelized portion of Golden Valley Wash and includes areas mapped within the FEMA Special Flood Hazard Areas (SFHAs). Accurate floodplain mapping was essential to assessing the development potential of the site and addressing misclassifications based on outdated FEMA data.
Scope of Services
Terraphase performed a comprehensive hydrologic evaluation using HEC-HMS to calculate site runoff and estimate retention basin requirements for the 10-day, 100-year storm event. A detailed review of FEMA SFHAs and flood profiles was conducted to identify discrepancies between outdated flood mapping and current topographic data. Our team prepared a HEC-RAS hydraulic analysis for both corrected effective and proposed conditions and coordinated with the project design team to support floodplain revision efforts.
Additional work included environmental site assessment (ESA) compliance evaluations and preparation of a FEMA Conditional Letter of Map Revision (CLOMR) report and submittal.
Notable Accomplishments
- Led FEMA map revision and WOUS delineation
- Identified floodplain mapping errors using updated topography
- Supported ESA compliance and CLOMR submittal
Reno-Stead Airport Hydrologic Study and Flood Protection Planning
Terraphase prepared the technical drainage study and downstream two-dimensional flood analysis for the Moya Boulevard Extension and Air Logistic Facilities project at the Reno-Stead Airport in Nevada. As the first phase of a larger commercial development plan, the project required alignment with the related area drainage master plan and careful consideration of flood risk to nearby residential areas.
Scope of Services
Terraphase’s efforts included upstream hydrologic analysis, runoff volume mitigation determination, and design of retention basin, storm drain, and channels. Our team also performed downstream two-dimensional hydraulic modeling to determine the impacts of undersized downstream channels on adjacent residences located along the overbanks. Upstream hydrologic analysis was crucial as the project is downstream of planned major detention basins designed to attenuate upstream flows passing through the site. Runoff volume mitigation was required due to the project’s location within the Silver Lake closed watershed and was achieved through Terraphase design of on-site retention basins. The site storm drain system was designed to convey peak flows from commercial areas and the proposed road to the flood channel.
Notable Accomplishments
- Completed major regional flood retention/detention alternatives analysis (HEC-HMS)
- Performed HEC-RAS two-dimensional modeling of multiple flood attenuation scenarios
- Aligned project drainage infrastructure with the regional Area Drainage Master Plan
- Delivered drainage solutions that addressed both on-site and downstream flood risks
Carson City Maxwell Regional Detention Basin Scoping
Terraphase is serving as the prime consultant for a multidisciplinary infrastructure project in Carson City, Nevada. Our team provides leadership in hydrologic and hydraulic analysis, environmental review, geotechnical evaluation, design development, and public outreach. The project aims to enhance basin performance while optimizing design efficiency and minimizing construction impacts.
Scope of Services
Terraphase’s responsibilities include refining previous hydraulic modeling using the FLO-2D model, conducting detailed geotechnical investigations, evaluating alternative basin configurations, and preparing the final plans, specifications, and estimates. The team also developed a revised basin layout that significantly reduced cut slope heights and earthwork volumes. Additional efforts include preparation of environmental documentation, public engagement, and coordination with regulatory agencies.
Notable Accomplishments
- Developed revised basin design, accepted by the City as an improved alternative, reduced cut slopes by 15 feet, and minimized earthwork
- Led refinement of hydrology and hydraulic modeling using FLO-2D
- Provided geotechnical input for embankment and outlet structure design
- Initiated early and ongoing public outreach to support project transparency and feedback
