A 12-section interactive reference guide covering core civil engineering topics used daily in site development. Includes the Rational Method (Q = CIA), Manning's equation for storm pipes, AASHTO pavement structural number design, Hazen-Williams water distribution, gravity sewer slopes, surveying, traffic LOS, NPDES stormwater permits, LID stormwater management, and civil drawing standards.
Each section targets a core civil engineering discipline or design method: standards and code overview (ASCE 7, AASHTO, NPDES, ADA), site grading and earthwork volumes (average end area, prismoidal formula, shrink/swell factors), Rational Method storm drainage (Q = CIA, IDF curves, Kirpich time of concentration, Manning pipe sizing), AASHTO 93 flexible pavement structural number design, water distribution (Hazen-Williams, fire flow, burial depths), gravity sewer minimum slopes, surveying (traverse, GPS accuracy, vertical control), traffic engineering (LOS, sight distance, parking, signal timing), NPDES environmental compliance and FEMA flood zones, stormwater LID and detention pond design (orifice and weir equations), civil site plan drawing standards, and a master quick-reference formula table.
Use the Prev / Next buttons at the bottom, or press the arrow keys on your keyboard. Click the ☰ menu button in the top-right to open the table of contents and jump to any section. The gold progress bar at the top tracks your position through all 12 sections.
This guide references current editions of ASCE 7-22, ACI 318-19, AASHTO Green Book, IBC, NPDES regulations, and AWWA standards. Local jurisdictions may adopt modified editions or have additional requirements — always confirm with the Authority Having Jurisdiction (AHJ) and local municipality before finalizing design values.
The Rational Method (Q = CIA) is valid for drainage areas up to approximately 200 acres with reasonably uniform land use. For larger watersheds, use the SCS/TR-55 method with unit hydrograph routing. Manning's equation assumes full-pipe flow for capacity calculations — actual design should verify that pipes flow at 75–85% of full capacity to allow for head buildup. AASHTO pavement structural number design requires a geotechnical investigation to establish subgrade resilient modulus (M_R) values.
Use Q = C × i × A, where Q is peak flow in cubic feet per second, C is the dimensionless runoff coefficient (0.85–0.95 for pavement, 0.25–0.35 for flat lawn), i is rainfall intensity in inches per hour from local IDF curves for the selected return period, and A is the drainage area in acres. The Rational Method is valid for drainage areas up to 200 acres with uniform conditions.
Gravity sewers must maintain a self-cleaning velocity of at least 2 ft/s when flowing full. Using Manning's equation with n=0.013, an 8-inch concrete pipe requires approximately 0.40% slope (0.004 ft/ft) to achieve 2 ft/s. Larger pipes require less slope. Many jurisdictions specify minimum slopes directly: 0.40% for 8-inch, 0.28% for 10-inch, 0.22% for 12-inch.
Sites disturbing 1 acre or more must obtain coverage under the EPA/state NPDES Construction General Permit (CGP). This requires developing a Stormwater Pollution Prevention Plan (SWPPP) before construction, installing BMPs (silt fence, construction entrance, inlet protection) before earth disturbance, and conducting regular inspections (typically every 7 days and after 0.25-inch rain events).
Per AASHTO 93, the structural number SN is calculated from the design equation relating ESALs (traffic loading), reliability R, serviceability loss ΔPSI, and subgrade modulus MR. For a typical residential street with MR=5,000 psi, 100,000 ESALs, 85% reliability, and ΔPSI=2.0, the required SN is approximately 2.0–2.5. A typical section meeting SN=2.5: 2-inch HMA (a₁=0.44 × 2 = 0.88) + 6-inch base (a₂=0.14 × 6 = 0.84) = SN ≈ 1.72; need to add subbase.