Wind Fetch¶
Wind fetch is the direction-dependent open-water distance available for wind to generate waves toward a receiving site.
Core Idea¶
Wind fetch is the uninterrupted distance over water, in a specified wind direction, available to generate local waves toward a receiving site. It is directional geography, not wave height. Wind speed and duration also matter, and short fetch can limit wave growth even when wind continues.
Scope of Application¶
The USACE reservoir manual, Appendix C Figure C-7, models 20 mph wind for 8 hours: 3.8-foot waves are possible with sufficient fetch, but a 10-mile effective fetch caps the result near 1.9 feet. These are modeled, not observed, heights. In a different setting, USGS Lower Pool 8 used 36 wind directions at 10-degree increments and 1989, 2000 and 2010/2011 land-cover maps to compute directional and weighted fetch for habitat planning; its accessible account supplies no per-cell distance. Storm surge and remote swell are separate considerations.
Clarity¶
State the receiving site, direction and whether the number is direct or model-specific effective fetch. Do not infer large waves from a long path without wind speed and duration, or treat storm-surge water-level rise as local fetch-generated wave height.
Manages Complexity¶
Fetch compresses an irregular map into a directional wave-model input while preserving the upwind obstacle limit. A single basin-wide maximum can hide important directional variation. No universal intrinsic cost tradeoff belongs to this geometric measure: fetch versus duration compares limiting inputs, not competing values; island-planning benefits and costs belong to a particular project.
Abstract Reasoning¶
Trace unobstructed over-water distance upwind of the site, then combine it with speed and duration under a specified model. Test whether distance or time limits locally generated wave growth and check separate swell and surge sources.
Knowledge Transfer¶
The directional-exposure pattern carries among reservoirs, river pools, lakes and bays; numerical wave estimates require appropriate depth, forcing and model assumptions. The water surface and wind–wave mechanism make fetch domain-specific, not a universal exposure-path prime. Distance is a measured-separation prerequisite for its directional paths, not a strict taxonomic genus; Flow and Gradient remain related live neighbors. Direct USACE PDF open failed in this pass; its original indexed Appendix C text supplies the cited quantities pending final visual check.
Relationships to Other Abstractions¶
Current abstraction Wind Fetch Domain-specific
Parents (1) — more general patterns this builds on
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Wind Fetch presupposes Distance Prime
Directional and effective fetch require measured open-water path lengths.
Hierarchy path (1) — routes to 1 parentless root
- Wind Fetch → Distance → Comparison → Self Checking
Neighborhood in Abstraction Space¶
Wind Fetch sits in a sparse region of the domain-specific corpus (91st percentile for distinctiveness): few abstractions share its structure, so a faithful description tends to retrieve it precisely.
Family — Unclustered & Miscellaneous (2551 abstractions)
Nearest neighbors
- Longshore drift — 0.82
- Tsunami — 0.81
- Bruun Rule — 0.79
- Iribarren Number — 0.79
- Reflection Seismology — 0.79
Computed from structural-signature embeddings · 2026-10-08