Beaverton Creek Mainstem Hydraulic Modeling Client: City of Beaverton; Beaverton, Oregon Completed: Summer 2003 Flowing through downtown Beaverton, Beaverton Creek is a complex maze of underground piping, inter-basin overflows, detention facilities, commercial developments and highway crossings. These difficult conditions have contributed doubts for many years regarding the adequacy and accuracy of the existing regulatory hydraulic models and the flood risks associated with this water body. Beginning with the Watersheds 2000 Project by Clean Water Services a comprehensive program for remapping the Beaverton Creek floodplain sought to consolidate these issues and previous studies into a uniformly applied current technology study. PWR was contracted by the City of Beaverton to prepare new and updated hydraulic models for portions of Beaverton Creek and its tributaries from its confluence with Erickson Creek upstream through the downtown core to its headwaters, a total of 11.2 River Miles. Specifically the work includes Erickson Creek, Hall Creek, North Hall Creek, Golf Creek, Middle Hall Creek, South Hall Creek, and some conversion of the Beaverton Creek main stem from the old HEC-2 format to the current standard HEC-RAS. Upper Beaverton Creek was studied by PWR under an earlier contract and will be included with all the above in FEMA floodplain remapping of the entire Tualatin River Basin by Clean Water Services (CWS), which is underway, since PWR is currently under contract with CWS to perform this work as well. Complex issues to be resolved in the Beaverton Creek Hydraulic Modeling project include: 1) a hydrodynamic model of overflows from Fanno Creek to Beaverton Creek in the vicinity of State Highway 217, 2) numerous long single and double barreled pipe culverts (nearly 2300-feet total) which will be studied using the WSPGW hydraulic model, and 3) detailed conveyance issues on the main stem from Hall Boulevard to Cedar Hills Boulevard as well as the lower reach of Erickson Creek.   Fanno Creek Flood Insurance Restudy Client: Clean Water Services; Washington County, Oregon Completed: 1999 Inaccuracies have long been suspected in the original Fanno Creek flood insurance study (FIS). These were highlighted by the large storm events of late '96 and early '97. In 1997 Clean Water Services (CWS) awarded PWR a contract to restudy almost 17 miles of Fanno Creek and its major tributaries.       The Fanno Creek flood insurance restudy (FIR) built on information PWR's team already developed for the Fanno Creek Watershed Management Plan. This comprehensive plan involved not only flood management but water quality and watershed health as well. The FIR also maintained many of the jurisdictional and stakeholder relationships developed during the watershed management plan. CWS is a cooperating technical partner (CTP) with FEMA which provides a waiver of fees for a restudy submittal. CWS also benefited from the fact that PWR is an experienced study contractor who has worked directly for FEMA, which substantially reduces the documentation required for the technical submittal. The full scope of work included: data gathering, aerial and ground surveys, detailed riverine hydraulics to delineate floodplain and floodway areas, preparation of multiple profiles and obtaining concurrence, development of work maps, a technical support data notebook (TSDN) as well as hard copy and electronic (DFIRM) submittals. PWR also provided client support during the public review phase.     Mompano Dam Rehabilitation Project Client: Beaverlake Development Corporation; Clackamas County, Oregon Completed: 1996 Staff of Pacific Water Resources, Inc. managed the preparation of construction drawings for spillway improvements to Mompano Dam in Clackamas County, Oregon. The project was initiated by an order of the State of Oregon to pass the probable maximum flood (PMF) of 6000 cfs. Project management was critical on this assignment since failure to meet the various stipulations found in the order would require breaching of the dam. The impoundment, Beaver Lake, is the central amenity of a 500-acre up-scale housing development; therefore, breaching was not an option. All work was performed in a highly charged environment of intense public scrutiny and threats of third-party legal action. In response to downstream landowners concerns, an innovative spillway configuration was developed that actually reduced downstream flow for small to medium flood events. Input from residents was received in the form of two 'Hydrology 101' classes presented to interested neighbors. The assignment included: formulation and development of various management and construction alternatives; design development and preparation of construction drawings for the recommended alternative; construction observation and administration; preparation of a controlled breach plan; development of an emergency action plan; development of and participation in a public involvement and education program; preparation of an interim emergency action/stormwater management plan; a dam break study to determine inundation areas in the event of catastrophic dam failure; and, preparation and acquisition of permits from Clackamas County, Oregon Department of Fish and Wildlife, Oregon Division of State Lands and the U.S. Army Corps of Engineers. The project was successfully constructed on time during the summer of 1995 and quickly tested by the flood of November 1996. The improvements performed flawlessly and no repairs were required. xxxxxxxxxxxxxxxxx Rock & Richardson Creeks Floodplain Remapping Client: Water Environment Services; Clackamas County, Oregon Completed: Ongoing In the next 2-10 years portions of the Rock and Richardson basins will urbanize as pressure mounts for additional development area within Portland's Urban Growth Boundary. Approximately 670 acres of the Rock Creek basin was annexed into the City of Happy Valley in 1998 and, Metro, along with Clackamas County, plans to annex the Damascus area of Richardson Creek in 2-5 years. The two basins comprise nearly 9300 acres and represent some of the highest development potential on Portland's fast growing east side.           Intense development pressure and regulatory demands brought about by the Endangered Species Act (ESA) as well as the Clean Water Act (CWA) have made identification and preservation of natural resources areas a critical issue. Mapping the floodplains is the first step in protecting water resources and identifying areas hazardous for human occupancy. PWR is developing the 100-year regulatory floodway and floodplain mapping for submittal to FEMA. Mapping for both waterways begins at their confluence with the Clackamas River and extends to headwater areas for a total of approximately 13 miles. Hydrology has been developed in concert with PWR's subconsultant, DHI, using Mike11 to establish peak flow rates for the 2-, 5-, 10-, 25-, 50- and 100-year floods. The project also involves managing and directing a significant survey effort to obtain the necessary cross-section information and establish reference marks in accordance with FEMA guidelines. The full work scope includes: field surveys, hydrologic analysis, river hydraulic analysis for multiple flood frequencies, floodway analysis, flood profile concurrence and the development of flood profiles, floodway data tables, floodplain and floodway work maps, DIFRM submittal, preparation of the technical support data notebook (TSDN), as well as electronic and hard copy submittals to FEMA. PWR is also assisting the client, Clackamas County, with public involvement and presentations of the new maps at open house meetings. Clackamas County is receiving funding from FEMA as a cooperating technical partner (CTP) for this project.   Seaside, Oregon Flood Insurance Restudy Client: Federal Emergency Management Agency; City of Seaside and Clatsop County, Oregon Completed: 2000 The original flood hazard studies prepared for Seaside, Oregon (population 5359) contained well known deficiencies due to the age of the study and the complex hydrology. For this reason the Federal Emergency Management Agency pushed this study ahead of others in 1998 in order to resolve issues surrounding underestimated peak flows and overflows from the Necanicum River. The Seaside Flood Insurance Restudy included 7.0 miles of the Necanicum River and 2.5 miles of Neawanna Creek, as well as completely new studies for 0.8 miles of Upper Neawanna Creek and 1.1 miles of Beerman Creek. The work scope included: aerial surveying, ground surveying and GPS control, hydrology studies, interviews with local residents and jurisdictional staff, preparation of floodplain and floodway maps and tables, and the DFIRM FEMA submittal with technical support data notebook (TSDN). The study scope originally included about 3.0 miles of Circle Creek until results indicated that Circle Creek was completely inundated by overflows from the Necanicum River. Hydrology produced by PWR's study indicated that the original flood insurance study (FIS) flows were significantly underestimated. For this reason, major split flows from the Necanicum River to Circle Creek and Neawanna Creek were not considered in the original models. As a result the final FEMA products indicated significantly greater flood depths and extents than previously estimated.