CH Cheat Sheet 2026

The 30 highest-yield CH facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. Thermocline stratification in a reservoir creates a water quality concern because the hypolimnion (bottom layer) may become: → Depleted in dissolved oxygen and enriched in reduced metals like iron and manganese
2. In an ADCP measurement, what does the term 'ensemble' refer to? → The average of multiple pings collected over a short interval
3. What is the significance of the Rayleigh criterion in the context of multibeam sonar resolution? → It establishes the minimum angular separation at which two targets can be distinguished
4. What is peer review in CH Environmental Impact Assessment? → Quality evaluation by qualified colleagues for improvement
5. The oxygen sag curve downstream of a wastewater discharge describes the relationship between: → Dissolved oxygen recovery and organic oxygen demand over distance
6. Which federal permit is typically required before conducting hydrographic surveys that involve discharge of any pollutant into US waters? → NPDES permit
7. What is the importance of continuing education for CH professionals in Environmental Impact Assessment? → Maintaining current knowledge and adapting to industry changes
8. Nonpoint source (NPS) pollution is best controlled through which management approach? → Best Management Practices (BMPs) applied at the source
9. In harmonic tidal prediction, the 'epoch' (κ) of a tidal constituent is: → The phase lag of the constituent relative to the equilibrium tide at the prime meridian
10. A hydrographer is tasked with evaluating the impact of upstream water withdrawals on a downstream estuary. Which indicator is most diagnostic? → Change in salinity intrusion distance during low-flow periods
11. On a UTM grid, what is the false easting assigned to the central meridian of each zone to avoid negative coordinates? → 500 000 m
12. In watershed-scale water quality management, a load duration curve (LDC) is used to: → Compare measured pollutant loads to allowable loads across a range of stream flows
13. When overlaying two polygon layers in GIS, which operation retains only the area that exists in BOTH input layers? → Intersect
14. The speed of sound used by an ADCP to convert travel time to range is primarily a function of: → Water temperature, salinity, and pressure (depth)
15. Which documentation is required in a NOAA Hydrographic Survey Project Instructions (HSPI) to define the geographic scope and priority areas of a survey project? → The survey limits diagram and priority area polygons with associated order requirements
16. Which ADCP blanking distance parameter defines the zone nearest the transducer where velocity data cannot be reliably collected? → Blank before transmit
17. Subsidence of a tide gauge benchmark would cause the recorded sea level trend at that station to appear: → Higher than the true sea level rise rate (apparent faster rise)
18. Which baseline data type is most relevant for assessing hydrographic survey impacts on submerged aquatic vegetation (SAV)? → Light attenuation and water clarity measurements
19. A hydrographer converts UTM coordinates to geographic coordinates. Which projection property is preserved in UTM? → Conformal (angle-preserving)
20. A 'finding of no significant impact' (FONSI) can be issued after which EIA document? → Environmental Assessment
21. The International Hydrographic Organization (IHO) publication 'S-44' primarily establishes: → Minimum standards for hydrographic survey accuracy by order classification
22. What is the primary horizontal datum used for nautical charts produced by NOAA in the United States? → NAD 83 / WGS 84
23. Which element distinguishes a 'programmatic EIS' from a standard project-level EIS? → It evaluates broad policies, plans, or programs rather than a single site-specific project
24. A 'co-tidal chart' displays lines of equal: → Time of tide (phase) at which high water occurs
25. A soil has a bulk density of 1.5 g/cm³ and a particle density of 2.65 g/cm³. What is the total porosity? → Approximately 43%
26. What is the primary source of uncertainty in ADCP discharge measurements caused by the region near the water surface? → The unmeasured top layer due to blanking distance and draft
27. A hydrographer is given coordinates in EPSG:4326. What coordinate reference system do these values represent? → WGS 84 geographic (degrees)
28. In the context of EIA for hydrographic surveys, 'mitigation' measures are best described as actions that: → Avoid, minimize, rectify, reduce, or compensate for adverse environmental impacts
29. Which type of satellite sensor is most commonly used to measure sea surface temperature (SST) in hydrographic studies? → Thermal Infrared (TIR) sensor
30. When conducting hydrographic surveys in a designated Critical Habitat under the Endangered Species Act, which agency must be consulted? → NOAA Fisheries or USFWS