Free PE Water Resources Exam Flashcards

Multiply unit-price quantities by their measured units, then add lump-sum allowances separately. Do not apply a linear-foot price to fittings, mobilization, or appurtenances unless the estimate explicitly includes them.

An activity is critical when delaying it delays the project finish. Critical-path review is about dependency logic and float, not simply the activity with the largest duration.

For alternatives with the same service period and performance target, the lower present-worth cost is economically preferred. Present worth already accounts for the time value of money.

Higher soil unit weight, greater retained height, surcharge, and water pressure all increase wall demand. Drainage matters because hydrostatic pressure can dominate an otherwise routine retaining problem.

It compares field dry density with the laboratory maximum dry density from a specified Proctor test. Moisture content matters because dry density, not wet density, controls acceptance.

Bearing capacity asks whether the soil can support the load without shear failure. Settlement asks how much deformation occurs under service loads. A foundation can satisfy one check and fail the other.

USCS classification uses grain-size distribution and plasticity behavior. Coarse soils are mainly split by gradation and fines content; fine soils are mainly split by liquid limit and plasticity index.

Match the material to pressure, corrosion, loading, joints, constructability, and service environment. Gravity sewers, force mains, and potable water mains may need different priorities.

Site control protects benchmarks, limits of work, utility locations, layout points, and adjacent facilities. Poor control can create drainage errors, encroachments, rework, or safety hazards.

It asks whether accumulation equals inputs minus outputs plus generation minus consumption. At steady state, accumulation is zero, which often simplifies the setup.

Hydraulic loading rate is flow divided by surface area, commonly used for basins, filters, clarifiers, and infiltration systems. Unit consistency is the main trap.

Solids loading is mass of solids applied per time, often normalized by area or volume. It combines concentration and flow, so both units must be converted before comparing to criteria.

Nominal detention time is volume divided by flow. It is a planning estimate; short-circuiting, dead zones, and mixing can make actual contact time lower than the simple ratio.

Weirs, flumes, meters, and similar devices convert water level, velocity, or pressure signals into flow. The correct method depends on channel conditions, calibration, submergence, and expected flow range.

For incompressible steady flow, Q = V A at each section. If pipe area decreases, velocity increases for the same flow; the water does not disappear.

The hydraulic grade line shows pressure head plus elevation head. The energy grade line adds velocity head. The EGL is above the HGL by V^2/(2g), except where velocity is negligible.

Darcy-Weisbach is broadly applicable when friction factor and units are handled correctly. Hazen-Williams is an empirical water-pipe equation and should not be used outside its assumptions.

Major loss is friction along pipe length. Minor losses come from fittings, entrances, exits, bends, valves, and expansions. In short systems, minor losses can be a major part of total headloss.

It is where the pump curve intersects the system curve. Changing pipe size, static lift, valve position, or roughness changes the system curve and can move the actual flow away from the desired value.

Cavitation risk rises when pressure near the impeller falls below vapor pressure. In PE terms, check available NPSH against required NPSH and watch suction lift, temperature, losses, and low wet-well levels.

Manning relates flow, roughness, hydraulic radius, area, and slope for uniform open-channel flow. The trap is using it where flow is rapidly varied, pressurized, or controlled by a structure.

Subcritical flow is deep, slow, and downstream-controlled. Supercritical flow is shallow, fast, and upstream-controlled. Froude number below 1 is subcritical; above 1 is supercritical.

Critical depth is the depth at minimum specific energy for a given flow. It separates subcritical and supercritical regimes and often appears near controls, transitions, and culvert behavior.

A hydraulic jump converts supercritical flow to subcritical flow and dissipates energy through turbulence. It is useful downstream of spillways, culverts, and drops when erosion protection is needed.

Inlet control means capacity is governed near the entrance. Outlet control means downstream water level, barrel roughness, length, and tailwater govern. The controlling condition determines the headwater calculation.

Q = C i A estimates peak runoff for small drainage areas when rainfall intensity matches the time of concentration. It estimates peak flow, not a full runoff hydrograph.

Time of concentration is the travel time from the hydraulically most distant point to the outlet. A shorter Tc usually means higher design rainfall intensity and higher peak flow.

An intensity-duration-frequency curve links rainfall intensity, storm duration, and return period. For the same return period, shorter durations usually have higher intensities.

A higher curve number means less infiltration and more direct runoff for the same rainfall. Impervious cover, poor soil infiltration, and wet antecedent conditions push runoff higher.

Peak flow is the maximum ordinate of the hydrograph. Runoff volume is the area under the hydrograph. Detention mainly reduces and delays the peak; infiltration or reuse can reduce volume.

A rating curve relates stage to discharge at a gauging location. It is site-specific and can shift after channel scour, sediment deposition, vegetation growth, or backwater effects.

Detention temporarily stores runoff and releases it over time. Retention holds water for infiltration, evaporation, reuse, or permanent pool storage. Confusing them changes both flow and volume assumptions.

Darcy's law relates groundwater flow to hydraulic conductivity, hydraulic gradient, and flow area. It is a flow law, so gradients and units must match the direction and scale of the problem.

A confined aquifer is under pressure beneath a confining layer. An unconfined aquifer has a water table open to atmospheric pressure. The storage behavior and drawdown response differ.

Their cones of depression overlap, increasing drawdown compared with a single isolated well. Interference can reduce available yield or increase pumping lift.

Biochemical oxygen demand consumes dissolved oxygen as organics degrade. High BOD loading can depress stream DO and harm aquatic life, especially when reaeration is limited.

A total maximum daily load is the pollutant amount a water body can receive and still meet water-quality standards. It is allocated among point sources, nonpoint sources, and a margin of safety.

Excess nitrogen or phosphorus can stimulate algal growth. When algae decay, oxygen demand rises and dissolved oxygen can fall, creating ecological stress or fish kills.

Sorption, dispersion, biodegradation, decay, and lower hydraulic gradients can slow or spread a plume. Advection moves contaminants with groundwater flow; retardation makes some chemicals lag behind the water.

Average day is long-term typical use. Maximum day is the largest daily demand used for supply and storage checks. Peak hour is the short-duration high demand that stresses distribution hydraulics.

Coagulation destabilizes particles, flocculation grows settleable floc, sedimentation removes much of it, filtration polishes the water, and disinfection inactivates pathogens.

Contact time supports pathogen inactivation, while residual helps protect water in the distribution system. Too little risks microbial safety; too much can worsen taste, odor, or byproduct concerns.

Hardness from calcium and magnesium can be reduced by lime softening, ion exchange, membranes, or blending. The right method depends on water chemistry, residuals, cost, and finished-water goals.

Infiltration is groundwater entering through defects such as cracked pipes and leaky joints. Inflow is stormwater entering through direct connections such as roof drains, cross-connections, or open manholes.

Primary treatment removes settleable and floatable solids by physical separation. Secondary treatment uses biological processes to remove dissolved and colloidal biodegradable organics.

F/M compares food load to microorganism mass. SRT estimates how long solids stay in the biological system. Together they affect treatment stability, sludge age, oxygen demand, and nitrification potential.

Nitrification converts ammonia to nitrate under aerobic conditions. Denitrification converts nitrate to nitrogen gas under anoxic conditions with a carbon source. The oxygen condition is the key distinction.

Thickening and dewatering reduce water content before hauling, disposal, or further treatment. Lower volume reduces handling cost, but stabilization may still be needed for odor, pathogens, and vector attraction.

Stabilize and control runoff before exposed soil leaves the site. Perimeter controls, inlet protection, construction entrances, sequencing, and prompt stabilization prevent sediment from becoming a downstream water-quality problem.

Good grading balances cut and fill where practical, directs runoff safely, protects adjacent facilities, avoids unintended ponding, and supports constructability. A visually smooth surface is not enough if drainage fails.