Drainage Engineering
Alliance understands the relationship the key elements of roadway drainage design: hydrologic investigation, lateral drainage (open ditch or storm sewer), cross drainage, and water quality evaluation. We understand the trade-offs between storm design frequency, cost, and safety, with the intent of providing an economical design that conveys surface water drainage along and through the project while minimizing adverse impacts on road users and surrounding areas. We are very familiar with the environmental requirements for water quality and permitting. Our engineers’ experience includes street drainage analysis and design; open ditch and storm sewer improvements; channel improvements, water quality facilities.
For a particular project, we anticipate balancing cost against design year to find a recurrence interval year that is acceptable to the client and within the project budget, while being mindful of existing safety concerns such as low water crossings or roadway overtopping on small storm events. We will model proposed structures against the design storm and work with the geometric, ROW and other design constraints to minimize impact to the 100-year floodplain upstream and downstream of the project (with the goal of no impact), and limiting impact to the waters of the US from any improvements and grading within a regulated waterway, with the intent of maintaining a natural channel. We will coordinate with Floodplain Administrators as needed, and prepare any necessary CLOMR and LOMR submissions.
We are familiar with both open ditch and storm sewer design, and can integrate either into the project design as required. For rural projects, open ditch drainage is typically desired, as the cost of additional right of way to accommodate ditches is typically less than the cost of a closed system. For such systems, we will work with the roadway designers to ensure a ditch design criteria that maintains the clear zone, allows for driveway access across the ditches, and maintains a water surface below the pavement section. For closed systems on curb and gutter roadways, we will work with roadway designers to ensure roadway grades that allow for positive flow to a curb and gutter system from the right-of-way (or to back-of-curb inlets), as well as sufficient free board below the curb for the storm sewer as designed. We will also provide a constructible storm sewer design that uses standard pipe types and sizes, and minimizes use of different inlet and manhole types.