Water Resources Engineering

G&D has extensive experience providing services related to water resources engineering such as flood studies, FEMA mapping studies, storm drainage design, dam repair and design, and water distribution system analyses. In addition, staff are experienced computer modelers successfully completing floodplain development studies, water distribution master plans, and sewer capacity analyses.

G&D often performs hydrologic analyses of the identified problem area's drainage basin using appropriate software tools in conformance with the Client's requirements. G&D has extensive experience in the commonly used tools that rely on the SCS unit hydrograph methodologies including HEC-1, HEC-HMS, etc. and use them for the performance of the hydrologic analyses to model storms of various return frequencies and durations. After development of the hydrograph information, a hydraulic model is typically developed.

If appropriate, computer-based hydraulic models are constructed of the project study area. Alternatively, other desktop methods (e.g., nomographs or spreadsheets) are used to evaluate a given structure. G&D conducts hydraulic analyses and other calculations as needed to evaluate the hydraulic performance of the subject drainage network. For example, culvert capacities are checked with respect to the accepted design criteria (e.g., 25-year storm for residential and collector roads). Peak stages are then reported and compared to critical elevations such as finished floor or road crest. G&D has extensive experience with a wide variety of hydrologic/hydraulic analysis and modeling tools including HEC-1, HEC-2, HEC-RAS, HEC-HMS, HY-8 and SWMM, which are all public-domain models available at no cost to our clients.

McDonald Farm Pond, Charlotte Storm Water Services

As part of our ongoing Open-Ended services contract with the City of Charlotte Storm Water Services (CSWS), G&D has begun planning the rehabilitation of the McDonald Pond dam and spillway. The existing primary spillway consists of dual corrugated metal pipes (CMP), which are badly corroded. In addition, the downstream spillway channel is eroding and the dam is subject to excessive seepage. Due to the compromised nature of the dam, G&D advised the City to prepare a "Dam Breach Risk Reduction" plan immediately, and prior to the design of the ultimate suite of improvements.

The proposed repair consists of replacing the existing primary spillways, lowering the normal pool elevation, and re-aligning the discharge channel so that it is off of the dam and is on stable native material. Construction of the repair is scheduled for this summer. Meanwhile, G&D is proceeding with the design of the overall improvements that will bring the existing farm pond, as much as possible, up to current City standards for a stormwater best management practice (BMP). The proposed improvements consist of installing a riser-barrel primary spillway structure, an overflow spillway, and replacement of significant fractions of the embankment material. HEC-1 and HEC-RAS models are being used to evaluate the improvement alternatives. The HY-8 model was used to develop rating curves for the primary spillway and to evaluate a downstream culvert.

http://charmeck.org/stormwater/Projects/Pages/McDonaldPond.aspx

Raintree Pond at Hole 4, Charlotte Storm Water Services

The G&D and LandDesign team is assisting the City of Charlotte Storm Water Services in developing and implementing a repair plan for the Raintree Pond at Hole 4. The dam is located on a golf course and the existing concrete primary spillway is failing as shown.

The scope of work completed by G&D includes preparation of a preliminary engineering report, field survey, hydrology and hydraulics evaluation, regulatory status and hazard classification (low hazard), condition assessment, geotechnical investigations, preparation of storm drainage easement exhibits, and the development of pond preservation and enhancement alternatives. G&D has completed design of the repairs, and the $221,000 project is currently under construction. The design includes limited dredging, a siphon system and spillway repair using economical gabions and reno mattresses.

http://charmeck.org/stormwater/Projects/Pages/RaintreePond.aspx

Culvert Replacement Projects, City of Newton

For the City of Newton, G&D planned and designed the replacement of three roadway culverts that were failing, leading to frequent road overtopping and destabilization of the road beds. Using the HEC-HMS model and the HY8 model, G&D designed replacement culvert systems that consisted of RCP or concrete box culverts. G&D performed the design, prepared associated contract documents, and oversaw bidding of the construction project. One of the culverts was located in the FEMA regulated floodplain and a CLOMR was obtained prior to construction. Construction has been successfully completed on all three road crossings.

UNCC Cameron Culvert Replacement Project

As part of a road repaving project, a Gavel & Dorn Engineering, PLLC (G&D) construction inspector performed an inspection of the then existing corrugated metal pipe-arch (CMP) culvert under Cameron Boulevard at the intersection with Mary Alexander Road on the campus of the University of North Carolina at Charlotte (UNCC). Approximately 2/3 of the pipe invert (total culvert length is approximately 88 feet) of the existing CMP was found to be missing due to the combined effects of corrosion and erosion as shown in Figure 4. Along approximately 1/3 of the pipe, the subgrade soil at the invert was washed out, and a large void space has developed around both sides of the pipe.

Since a CMP is classified as a flexible structure that requires interaction with soil for stability, loss of the invert can result in severe distortion and collapse of the culvert at any time during a rain event. A likely consequence of such a failure would have been possible flooding, washout of the road, its associated shut down to through traffic and also the possible loss of utilities that cross the culvert. G&D alerted the University and was directed to perform a fast-track design of the replacement culvert system.

The engineering design services scope of work included geotechnical analysis, hydrologic and hydraulic analysis (using HY-8), design of utility supports, and construction observation services. Due to steep slopes downstream of the culvert, a gabion earth retaining wall was also required. The construction of the 96-inch RCP replacement culvert was performed by the contractor as a change order to the repaving project contract (approximate construction cost of $300,000) and completed within a few months of the initial inspection with minimal disruption to the campus.

FEMA HEC-RAS Modeling

G&D has completed multiple FEMA modeling studies for various clients using the HEC-RAS model. As a subconsultant to Site Solutions, G&D prepared a "No Rise" certification for the Eighth Street Greenway project in Kannapolis. The "No Rise" was obtained for a proposed pre-fabricated pedestrian bridge. For UNCC, G&D obtained a Floodplain Development permit for the University's proposed new track and field facility located in the floodplain of Toby Creek. This effort required obtaining the City's latest FEMA models and revising per the proposed grading effort.

Freightliner Storm Drainage Improvements Project

Freightliner, owned by Daimler, manufactures heavy truck components at its Gastonia, North Carolina plant. The site's drainage network included multiple best management practices (BMP's) because it is located in a critical water supply watershed. The BMP's required maintenance and included multiple dry detention ponds and a wet retention pond.

In addition, there were multiple outfalls and other areas that were subject to erosion. Finally, the owner also requested that spill containment valves be installed at all outfalls. G&D developed a cost proposal that included construction to address the specified needs, performed design and oversaw construction, and completed the project on time and on budget.