Chartered Civil Engineer (ICE) Water, Hydraulics and Environmental Engineering Flashcards

24 sample cards from the Water, Hydraulics and Environmental Engineering deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. Outline the basis of statistical flood frequency analysis using annual maxima.

   A series of annual maximum peak flows is fitted to an extreme-value probability distribution (e.g. Gumbel/EV1, GEV, or in the UK the Generalised Logistic distribution used in the Flood Estimation Handbook). The fitted distribution gives the flood magnitude $Q_{T}$ for any return period $T$ via the growth curve scaled by the index flood (median annual flood $Q_{MED}$).

2. What is the standard UK method for flood estimation and its two main approaches?

   The Flood Estimation Handbook (FEH) is the UK standard. Its two approaches are: (1) the statistical method — using $Q_{MED}$ and a pooled growth curve from gauged/ungauged catchment descriptors; and (2) the rainfall-runoff method (e.g. ReFH — Revitalised Flood Hydrograph model) — converting a design rainfall to a flood hydrograph.

3. Distinguish fluvial, pluvial, and coastal flooding.

   Fluvial flooding is river/watercourse overtopping its banks from excess catchment runoff. Pluvial (surface water) flooding results from intense rainfall overwhelming drainage before reaching a watercourse. Coastal flooding arises from high tides, storm surge, and wave action, often combined with high river levels (tide-locking).

4. What are the EA Flood Zones used in UK flood risk assessment and planning?

   Flood Zone 1: low probability, annual fluvial probability $< 0.1\%$ ($<1$ in 1000). Flood Zone 2: medium, fluvial $0.1\%$ to $1\%$ (1 in 100 to 1 in 1000). Flood Zone 3a: high, fluvial $\geq 1\%$ (1 in 100 or greater), tidal $\geq 0.5\%$. Flood Zone 3b: the functional floodplain that stores or conveys flood water.

5. Describe the hierarchy of flood risk management options (the sequential approach).

   Apply the sequential test to steer development to lowest-risk land first. Then manage residual risk by: avoid, resist (defences/barriers), and resilience (designing to recover quickly, e.g. raised floor levels, flood-resistant materials). Manage flood flows via storage/attenuation, conveyance, source control (SuDS), and provide warning/evacuation and freeboard allowances for climate change.

6. State the four pillars of SuDS design (the SuDS management train objectives).

   SuDS aim to manage surface water sustainably by balancing four pillars: (1) water quantity (control runoff rates and volumes, ideally to greenfield runoff); (2) water quality (remove pollutants); (3) amenity (create better places for people); (4) biodiversity (create and enhance habitat).

7. Give examples of SuDS components and the concept of the management train.

   Components include green roofs, permeable paving, filter strips, swales, infiltration trenches, soakaways, detention basins, retention ponds, wetlands, bioretention/rain gardens. The management train treats and attenuates runoff in sequence: source control, then site control, then regional control, mimicking natural drainage and reducing flow to receiving waters.

8. What is the target discharge rate for new SuDS development and define greenfield runoff?

   New developments should restrict surface water discharge towards the greenfield runoff rate — the rate that would occur from the site in its natural, undeveloped state (commonly characterised by the 1-year greenfield rate, $Q_{BAR}$, or $Q_{1}$). Attenuation storage is provided to limit peak discharge to this rate for the design return period plus a climate change allowance.

9. How is per-capita water demand and total demand on a distribution network estimated?

   Total average daily demand $$Q = P \times q$$ where $P$ is population served and $q$ is per-capita consumption (UK domestic typically around $140\ \text{litres/person/day}$). Network design must also account for peak factors (peak hour/peak day), non-domestic demand, leakage, and fire-fighting flows.

10. What design rule governs pressures and looping in a water distribution network?

    Networks are designed as looped (ring) systems for reliability and to balance pressures, rather than dead-end branches. A minimum residual pressure (commonly about $15\ \text{m}$ head, ~1.5 bar, at the customer) must be maintained at peak demand, while limiting maximum pressure and velocity (typically $1$ to $2\ \text{m/s}$) to control surge and leakage. Analysis uses Hardy Cross / hydraulic solvers to balance heads and flows.

11. List the conventional sequence of unit processes in potable water treatment.

    Screening, coagulation (e.g. adding aluminium sulphate / ferric salts), flocculation, sedimentation (clarification), filtration (rapid gravity or slow sand), and disinfection (chlorination, UV, or ozone), often with pH correction and fluoridation. The aim is to remove turbidity, pathogens, colour, and dissolved contaminants.

12. Explain the roles of coagulation and flocculation in water treatment.

    Coagulation rapidly mixes a coagulant (e.g. $\ce{Al2(SO4)3}$ or ferric chloride) to neutralise the negative charge on colloidal particles, destabilising them. Flocculation is slow, gentle mixing that allows the destabilised particles to collide and aggregate into larger, settleable flocs, which are then removed by sedimentation and filtration.

13. What is the main disinfection chemistry of chlorination, and why maintain a residual?

    Chlorine added to water forms hypochlorous acid: $$\ce{Cl2 + H2O -> HOCl + HCl}$$ $\ce{HOCl}$ is the active biocide. A free chlorine residual is maintained through the distribution network to guard against recontamination, but excess can form disinfection by-products (e.g. trihalomethanes).

14. Compare combined and separate sewer systems.

    A combined sewer carries both foul (wastewater) and surface (storm) water in one pipe; cheaper historically but can cause combined sewer overflow (CSO) spills in storms. A separate system uses distinct foul and surface water sewers, keeping clean stormwater out of treatment works and reducing overflow pollution; preferred for new development (often with SuDS).

15. What self-cleansing criterion governs gravity sewer (foul) design?

    Sewers are sized to achieve a minimum self-cleansing velocity (commonly about $0.75\ \text{m/s}$ for foul sewers at peak flow, ~$1\ \text{m/s}$ for storm) to prevent deposition of solids. Gradients and pipe sizes are chosen so this velocity is reached; flow is usually computed with the Colebrook-White or Manning equation for part-full pipes.

16. Define BOD and COD and explain their significance in wastewater.

    BOD (Biochemical Oxygen Demand) is the oxygen consumed by microorganisms degrading organic matter, usually measured over 5 days at $20^{\circ}\text{C}$ ($\text{BOD}_{5}$). COD (Chemical Oxygen Demand) is the oxygen equivalent of organic matter oxidisable chemically. COD $>$ BOD; both indicate organic pollution load and the strength of wastewater.

17. List the stages of conventional wastewater (sewage) treatment and what each removes.

    Preliminary: screening and grit removal (rags, grit). Primary: sedimentation removing settleable solids and some BOD. Secondary: biological treatment (activated sludge or trickling filter) removing dissolved/colloidal organic BOD via microorganisms, followed by final settlement. Tertiary: polishing for nutrients (N, P), suspended solids, and disinfection before discharge.

18. Explain the activated sludge process.

    Wastewater is aerated in a tank where a suspended culture of microorganisms (mixed liquor) oxidises organic matter. The mixture passes to a secondary clarifier; settled biomass (sludge) is partly returned (RAS) to maintain the population and the rest wasted (WAS). It removes BOD and, with suitable configuration, nitrogen (nitrification/denitrification) and phosphorus.

19. What are the main statutory stages of an Environmental Impact Assessment (EIA)?

    Screening (is an EIA required?), scoping (what issues/impacts to assess), preparation of the Environmental Statement (baseline, impact prediction, mitigation), consultation (statutory consultees and public), decision-making by the competent authority, and monitoring of significant effects after consent. UK EIA follows the EIA Regulations transposing the EIA Directive.

20. Define the mitigation hierarchy applied in EIA and ecological design.

    Address impacts in priority order: (1) Avoid (prevent the impact, e.g. relocate works); (2) Minimise/reduce (lessen magnitude/duration); (3) Restore/rehabilitate (repair affected receptors); (4) Offset/compensate (provide equivalent gains elsewhere for residual impacts). Avoidance is always preferred; compensation is the last resort.

21. What is PAS 2080 and the three categories of carbon it addresses?

    PAS 2080 is the standard for carbon management in buildings and infrastructure across the whole value chain. It addresses capital carbon (embodied, from materials and construction), operational carbon (from operating the asset), and user carbon (associated with users/occupants), promoting reduction through the carbon hierarchy: avoid/build nothing, build less, build clever, build efficiently.

22. State the principles of the circular economy as applied to civil engineering resource efficiency.

    Design out waste and pollution, keep materials and products in use at their highest value (reduce, reuse, repurpose, remanufacture, recycle), and regenerate natural systems. In construction this means designing for longevity, adaptability and disassembly, specifying recycled/secondary materials, and minimising raw material extraction and landfill (the waste hierarchy).

23. Define Biodiversity Net Gain (BNG) and its mandatory minimum in England.

    BNG is an approach requiring development to leave biodiversity in a measurably better state than before. In England it is mandatory to deliver at least a $10\%$ net gain in biodiversity, measured using the statutory biodiversity metric (habitat units), secured and maintained for a minimum of 30 years, after applying the mitigation hierarchy on-site first.

24. Contrast climate change adaptation with mitigation and give examples of adaptation/resilience measures.

    Mitigation reduces greenhouse gas emissions (the cause); adaptation manages the unavoidable impacts (the effect). Adaptation/resilience examples: increased design freeboard and climate change allowances on flood defences, larger drainage and SuDS capacity, heat-tolerant materials, robust/redundant networks, managed retreat, and flexible designs that can be upgraded as future climate data evolves.

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