PSC’s Hydrology / Hydraulics experience includes the disciplines necessary to fully support the private and public sector’s storm water engineering needs. Our philosophy is to partner our comprehensive, multi-disciplined practice and dedicated Hydrology / Hydraulics team members with our clients to help them identify and address their current and future storm water management solutions. PSC emphasizes the development of long-term, working relationships with our clients.
Scope of Services
Drainage Master Plans
Flood Insurance Studies
Storm Sewers and Inlets
Geographic Information System
Computer Model Simulations
Construction Administration Services
Emergency Action Plans
Industrial Storm Water
We offer full-service engineering and architectural design capabilities. As a result of our expertise, hard work and dedication, we have established trusted partnerships with our clients. PSC also maintains excellent working relationships with local, state and federal agencies and has the expert knowledge to guide clients through hydrological and hydraulic design criteria and requirements.
National Society of Professional Engineers (NSPE)
American Society of Civil Engineers (ASCE)
Texas Floodplain Management Association (TFMA)
American Institute of Architects (AIA)
American Society of Landscape Architects (ASLA)
International Interior Design Association (IIDA)
U.S. Green Building Council (USGBC)
American Association of Airport Executives (AAAE)
Storm Sewers and Inlets
Storm sewers and their associated inlets operate under gravity flow hydraulics and convey water underground to a suitable point of discharge. Storm sewers also serve as surface water control for highways, streets, railroads, airports, and urban development. The photo to the left shows the stabilized discharge point of a nearly 14-mile long system that controls the water levels in 12 small city lakes across Lubbock, TX. An inlet structure for this stormwater management system is shown below. Over 3 miles of storm sewer was installed by tunneling methods for this project. Our engineers are well-experienced in storm sewer and inlet designs, as well as performing computer simulations of the system design. Experience with large-scale, retro-fit designs in heavily developed areas has resulted in unique and progressive construction feasibility experience that our engineering staff applies to every new storm sewer design.
Flood Insurance Studies
Communities participating in, or that wish to participate in, the National Flood Insurance Program (NFIP) are governed by the federal regulations of that program and must adopt flood damage prevention ordinances. Enforcement of those ordinances rely heavily on Flood Insurance Rate Maps (FIRMs). The FIRM is determined from hydrological and hydraulic studies that define the 1% annual chance flood and the 0.2% annual chance flood. Often, changes in the community dictate new studies and maps to replace older studies, to extend existing studies to accommodate new land development, or to perform detailed studies where only approximate flood zone delineations exist. These studies are defined as map changes and must conform to the Federal Emergency Management Agency’s (FEMA) requirements for computer model simulations, mapping accuracy, and mapping standards. PSC’s engineers are also Certified Floodplain Managers (CFM), and are familiar with the FEMA and NFIP requirements.
Feasibility studies enable the client to review multiple concepts and the physical and economical viability of those concepts. The feasibility study depicted at left for the City of Midland, Texas analyzed various planned development land uses and surface runoff detention storage locations enabling the client to evaluate which concept to adopt. Other feasibility studies involve publicly-funded infrastructure. The study to the right depicts the adopted storm sewer outfall concept in the City of Lubbock, Texas to provide drainage relief around several small city lakes. The computer model simulation setup for this study is shown below. Such feasibility studies indicate whether a proposed action will achieve the desired result and in some cases reveal promising avenues for further analysis. A feasibility study is often a prerequisite for proceeding with multi-million dollar projects, especially where public funds or bond issues are at stake.
Open Channels and Culverts
Open channels are usually the least expensive engineered conveyance for storm water. They are composed of a variety of materials such as natural earth or erosion resistant materials. Open channels convey water at high capacity flow rates. Where these channels cross transportation related facilities or obstacles, a culvert or bridge is necessary for continued water conveyance. Large culverts approach bridge-class status and are designed accordingly. The channels and culverts are intended to hydraulically interact in an efficient manner and are usually provided with safety end treatments. The project shown on these pages is an economic development business park that incorporated concrete-paved streets, a boulevard-type center channel, and culverts at crossing locations. The channel design incorporated rock riprap stabilization, safety end treatments, vegetated and concrete linings for the channel and landscaping features.
Energy Dissipation and Stabilization
Flowing water at high velocity will often scour channels and basins when the water’s energy is not dissipated properly. Scouring also occurs when a basin or channel is not stabilized and soil displacement occurs. This leads to adverse structural conditions. The site geology will normally dictate whether energy dissipation or surface stabilization is needed relative to the hydraulic engineering of the storm water conveyance. Shown below is a baffled apron outlet to decrease the water’s energy prior to entering a detention basin for a project in El Paso, Texas. On the left, the site conditions and hydraulic engineering called for rock riprap and geotextiles for a West Texas landfill closure, including concrete-lined perimeter channels discharging into stilling basins. To the right, a combination of rock riprap stabilization, channel invert concrete lining and vegetation were used for this subdivision in Lubbock, Texas.
Storm Water Detention and Retention
The purpose of storm water detention is to capture the storm water runoff and then release it at a slower flow rate. Detention is often dictated by local development standards that require post-development storm water flow rates to not exceed pre-development flow rates. In other cases, the runoff rate is limited because of downstream capacity limitations. The development project, shown below, incorporated detention because of off-site flow capacity limitations. Retention is designed to retain storm water runoff and to then allow that runoff to evaporate or infiltrate until the retention basin’s water level recedes. The project shown on the right required a storm water retention plan to avoid discharge to a smaller natural lake. Retention can also be dictated by industrial storm water regulations, local development criteria or site conditions.
Often, physical and topographic conditions prohibit the operation of drainage systems solely by gravity hydraulics. In these instances, a pump station is needed for final discharge to the receiving stream or lake. An example is shown below where this pump station receives storm water runoff via a 120-inch diameter concrete pipe storm sewer and pumps that storm water into a 120-inch outfall concrete pipeline that discharges to the Rio Grande River in El Paso, Texas. The pumps energize in a staggered manner according to the flow rate entering the station. PSC engineers have designed a number of storm water pump stations and possess pre-certifications from the Texas Department of Transportation (TxDOT) for pump station designs. The El Paso station below uses submersible propeller pumps, while the TxDOT IH-27 station depicted at right uses vertically-mounted motors driving vertical turbine pumps.
Emergency Action Plans
Emergency action plans are developed to prepare for the threat that dams and reservoirs can pose in the event of a catastrophic failure. In performing an emergency action plan analysis, the dam is considered to be breached catastrophically and the resultant estimated flood wave is modeled for downstream travel time and depth. Using this model, an inundation map is prepared with time-to-flood details and water depths that illustrate the amount of time for warning and evacuation, plus the severity of the risk. Included in the emergency action plans are local emergency contacts, as well as a list of downstream property owners or occupants. The example shown below is an emergency action plan that PSC developed for a site at Rusk, Texas. The site shown at left is located in Howard County, Texas and also required our emergency action plan services.
Industrial Storm Water
Industrial storm water is regulated under the Environmental Protection Agency’s Storm Water Regulations according to the Standard Industrial Classification (SIC) of the facility. Some facilities require interception of storm water that comes in contact with stockpiles, tanks, process piping, or other site features. This intercepted water then must be tested for listed contaminants and treated if contaminant concentrations exceed regulatory limits. Other facilities can avoid the sampling and testing requirements by capturing and completely storing the volume of storm water from a four percent (25-year) probable storm event. For other SIC industrial facilities that have little contact water that could be contaminated, Storm Water Pollution Prevention Plans are developed and updated on a regular basis, however runoff water capture or retention is not usually required.
PSC has performed numerous hydrologic and hydraulic projects for transportation related infrastructure. Our expertise includes airports, freeways, thoroughfares, streets, and railways. PSC’s hydrologic and hydraulic engineers are pre-certified by TxDOT in multiple hydrologic and hydraulic categories. Additionally, our firm is on the list of approved engineering firms for two major railway companies. For our airport clients, we are aware of the wildlife attraction hazard that standing water poses to safe aircraft operations. We have the expertise to mitigate this hazard, while adhering to federal and state design criteria. Regarding state highway clients, we are well-versed in the criteria and software model requirements necessary to design a variety of drainage features including storm sewers, culverts, open channels and bridges. We have the ability to take any of these transportation categories and incorporate numerous drainage features into the final design.