Mapping methods
Two linked questions: what habitats are mapped along Homestake Creek, and how much mapped wetland ground lies beneath our modeled full-pool zones for the four potential Whitney dam sites?
Method in plain terms
Homestake’s fens and connected wetlands are the ecosystem represented here. “Potential Fen” remains the source label for particular mapped areas, with their original confidence and verification status retained in the calculations.
We used the Colorado Natural Heritage Program’s mapped wetland and potential-fen outlines. For the downstream map, we retain complete wetland and pond polygons and classify mapped creek contact and terrain-supported continuity across the valley floor. For the reservoir comparison, we overlay the same inventory with each modeled water surface and measure the ground they share.
Across the expanded map’s two panels, 310 mapped-water, 197 mapped-wetland and 26 Potential Fen source records intersect the display. A record shown in both panels is counted once. These are inventory records, not acres or predicted damage.
About 81.4 unique acres of mapped wetland and Potential Fen ground lie inside all four modeled full pools after mapped-water categories are removed. We count ground covered by overlapping polygons once, rather than adding their acres twice.
Downstream habitat map
The map follows Homestake Creek from Whitney through Blodgett and Hornsilver Campground to the Eagle River confluence near Red Cliff. Whole wetland complexes remain visible across the valley floor, with mapped water connections, potential-fen habitat and the A–D reservoir outlines for context.
The panels overlap at Blodgett and have separate scale bars. Green shows linked complexes, amber marks unresolved valley connections and pale shading retains other inventory context. Hatching identifies mapped potential fens. Open full-size map · Download complete mapped features
Connected wetlands
Beaver ponds and branching channels spread water across the valley floor, and shallow groundwater connects adjoining wetland ground.
The calculation retains complete mapped wetland and pond boundaries. It follows mapped channel links and reviews valley-floor continuity across inventory gaps using terrain. Uphill tributary settings remain separately visible.
Lower creek levels can reduce wetland replenishment and increase drainage of connected groundwater. A spring or seasonal creek can contribute water while the wetland remains sensitive to Homestake Creek.
36 linked complexes contain 362.1 unique acres of mapped wetland and potential-fen habitat. That whole-complex total includes one 49.2-acre complex crossing the upstream Whitney assessment endpoint; the other 35 complexes contain 312.8 acres. The lower reach from Blodgett to the Eagle River confluence contains 137.0 acres.
Mapped creek contact accounts for 328.1 acres; documented valley-floor continuity adds 33.9 acres. Another 15.4 acres in valley-margin complexes remain visible in amber with unresolved connections. The inventory measures mapped habitat, with the timing and severity of drying governed by flow, pond levels and groundwater.
Of the 362.1 linked-complex acres, the ground outside each modeled reservoir is A: 296.1 acres; B: 324.7; C: 316.0; D: 287.3. These remainders and the direct-inundation figures answer different questions. The methods retain the upstream crossing complex and account for each intersection, so overlapping acres are not added twice.
The wetland/potential-fen union is 362.1 acres. The mapped ponds cover 15.7 acres, including 0.3 acres overlapping potential-fen mapping. The combined wetland, potential-fen and pond union is 377.5 acres.
Reservoir comparison
We intersected each modeled pool with the September 18 source polygons. Pool options differ, so each has a different wetland and Potential Fen overlap. The shared area is the geographic intersection of all four pools with those mapped habitats.
A: 127.36 acres; B: 85.40; C: 94.91; D: 134.82. These are unique mapped wetland and Potential Fen acres inside each pool, excluding mapped-water categories.
81.40 acres are inside all four water surfaces. The union across any option is 140.66 acres. These are different geographic questions, so the individual areas are not added together.
Calculation method
The mapped source, processing rules and conversion are recorded here so the plain-language totals can be reproduced.
The map merges complete September 18 exports of the CNHP Wetlands, Fen Mapping and USGS 3DHP services with October 5 lower-creek exports. Shared source IDs were deduplicated after checking that their geometries were identical. The Whitney-to-Blodgett panel covers EPSG:32613 eastings 377,000–383,700 m and northings 4,363,500–4,371,500 m. The Blodgett-to-confluence panel covers eastings 380,650–384,070 m and northings 4,369,900–4,374,380 m. Source counts use the union of those display windows.
ESRI rings were reconstructed with symmetric difference and invalid polygons repaired. Full source polygon geometries are retained in the downloadable GeoJSON; the panels clip display only. USGS stream lines, terrain and road data supply geographic context. The two panels overlap and use separate scale bars. The A–D outlines use the reservoir solver and 10 m terrain inputs.
The current whole-complex calculation starts at the earliest existing A–D dam-axis crossing on Homestake Creek and ends at the Eagle River confluence. It groups complete mapped wetland and pond polygons, follows their mapped creek connections, and records terrain-supported valley-floor continuity. Continuous river-network polygons supply context without automatically extending the linkage classification uphill along tributaries. Individual terrain reviews stop two such routes at existing feature boundaries and add valley-floor complexes across inventory gaps. No distance, elevation or slope threshold determines inclusion. Source classifications and polygon identifiers remain attached to every feature. Areas are dissolved in EPSG:32613 before division by 4,046.8564224 square metres per acre.
The connected-pool solver produces full-pool water-surface triangles for A, B, C and D. Their exact unions are intersected with all source inventory polygons in projected EPSG:32613 coordinates. Overlapping source polygons are dissolved before combined area is reported. Mapped-water inventory categories are excluded from the wetland-and-fen ground measure.
Shared acres = area[(W ∪ F) ∩ A ∩ B ∩ C ∩ D] ÷ 4,046.8564224Here W is the union of wetland inventory polygons in non-water categories, F is the union of Potential Fen polygons, and A–D are the four modeled water surfaces. Mapped-water feature records are omitted by category before the union; their geometry is not subtracted from an overlapping non-water polygon. Area in the numerator is square metres; 4,046.8564224 square metres equal one acre. A single-option figure uses only that option’s water surface. “Any option” replaces the intersection of A–D with their union. Each feature count requires a positive-area intersection, including partial overlaps. The source snapshot and solver input SHA-256 fingerprints, which detect a changed input file, are preserved in the data record.
Potential Fen is an inventory class, rather than a field-confirmed peat-depth finding for every polygon. Connection classes identify mapped surface links, terrain-supported valley-floor continuity and other mapped wetland settings. The acreage describes the mapped habitat represented by each class; the timing and severity of drying depend on changes in flow, pond levels and groundwater. The reservoir intersections estimate exposure to our modeled full-pool boundaries for the potential dam sites. The mapping does not assign final road, pump, tunnel, pipeline or electrical alignments.
Reservoir model
The model places approximate dam axes from Aurora Water’s 2019 draft map on USGS bare-earth terrain. It finds ground connected to the pool behind each dam and sums the water above it at the selected level. These are modeled flood zones for the potential dam sites in the partners’ plans.
The terrain is a 10 m USGS 3DEP grid at 1× scale. A connected-pool search includes ground below the selected water level behind a modeled earth-and-rock embankment. Each terrain triangle is clipped at the waterline and at the modeled dam face. For every wet triangle, volume in cubic metres is Vtriangle = A × (d1 + d2 + d3) / 3, where A is horizontal triangle area in square metres and each d is water depth in metres at a vertex. The sum is divided by 1,233.48183754752 cubic metres per acre-foot and the on-screen amount is rounded to the nearest 10 acre-feet. Pool height is a percentage of the modeled water-level range, not a percentage of storage volume.
Display ceilings are B 6,850, C 10,000, A 15,000 and D 20,000 acre-feet. Terrain and dam-height limits can produce a lower full-pool volume. These ceilings sit within the utilities’ published 6,850–20,000 acre-foot range. Approximate dam locations come from the 2019 draft map; investigation points come from the 2019 drilling application.
Original maps and data
Whole-complex assessment completed October 6, 2026. Source exports: September 18 and October 5, 2026.
