Carroll CountyNew Hampshire
Madison, New Hampshire
1 high-hazard dam is rated in poor or unsatisfactory condition. Bedrock sits a median 52 ft down across 473 logs, deeper than the New Hampshire median of 20 ft.
- Live · as of Sep 11, 2026
- 9 public sources · method
- ← All towns
Median depth to bedrock
52 ft
middle half 18–95 ft · 473 logs
Bridges rated poor
0
of 2 inventoried
Poor high-hazard dams
1
National Inventory of Dams
FEMA repair $, Carroll County
$13.0M
federal share since 2010 · county-wide
01 · Dams & disasters
1 high-hazard dam needs work
FEMA Public Assistance is reported by county, so the figure below is Carroll County-wide context, not a Madison number.
| Dam | Condition | Built |
|---|---|---|
| Purity Lake DamSalmon Falls River | Poor | 1930 |
High hazard potential means failure would probably cost lives — it rates the consequences, not the dam’s condition.
FEMA Public Assistance, Carroll County
$13.0M
Federal share obligated across 185 projects in 11 declared disasters since 2010. The largest category is emergency protective measures (47%); roads & bridges took $5.2M.
02 · Ground
Deep ground: 50% of logs go past 50 ft before rock
From 473 depth-to-rock records inside Madison (NH DES well inventory). Logs cluster where people drill wells and bore for roads, so treat this as the town’s pattern, not a site answer.
Half of Madison's logs reach rock between 18 and 95 ft
Depth to bedrock: 10th–90th percentile whisker, middle-half box, median tick; dashed line = New Hampshire median.
median 52 ftNH 20 ft
050100 ft
n = 473 logsSource: NH DES well inventory
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| Depth to rock (ft) | Logs |
|---|---|
| 0–5 | 21 |
| 5–10 | 38 |
| 10–20 | 66 |
| 20–50 | 99 |
| 50–100 | 135 |
| 100+ | 114 |
Rock within 10 ft
16%
of logs (31% across New Hampshire). Shallow rock means ledge in excavations, refusal for driven piles and rock anchors rather than soil nails; deep ground means taller shoring and more groundwater. 50% of logs here go past 50 ft.
03 · Bridges
None of Madison's 2 bridges is rated poor
Every highway bridge and large culvert in the 2025 National Bridge Inventory that stands inside Madison. Median age 70 years.
0% good, 0% poor
FHWA good / fair / poor rating — the lowest of deck, superstructure, substructure or culvert.
- Good0 · 0%
- Fair2 · 100%
- Poor0 · 0%
n = 2 structuresSource: FHWA National Bridge Inventory 2025
▸ Show the numbers▾ Hide the numbers
| Built | Structures |
|---|---|
| 1950s | 2 |
04 · Next door
Madison and the 6 towns that border it
A dash means no data for that layer, not zero.
| Town | Poor bridges | Rock depth |
|---|---|---|
| Madison, NH | 0 / 2 | 52 ft |
| Tamworth, NH | 0 / 25 | 65 ft |
| Ossipee, NH | 0 / 24 | 75 ft |
| Conway, NH | 0 / 16 | 70 ft |
| Albany, NH | 2 / 11 | 50 ft |
| Freedom, NH | 1 / 7 | 48 ft |
| Eaton, NH | 0 / 3 | 30 ft |
Where these numbers come from
Method, sources & caveats
Madison is the Census county subdivision 3300345060 (Carroll County). Every record is placed here by its coordinates, not by the place name the source uses.
- Towns are Census county subdivisions: cities, towns, plantations, and Maine/New Hampshire unorganized territories and townships. Every record is placed in a town by its coordinates (point-in-polygon), not by the source's own place label — so a bridge in Roxbury counts for Boston and a well in 'North Waltham' counts for Waltham.
- Bridges: FHWA NBI 2025, highway structures ≥ 20 ft including large culverts. 'Poor' is FHWA's good/fair/poor rating (lowest of deck, superstructure, substructure or culvert ≤ 4). Percent-poor is shown only for towns with at least 5 structures.
- Depth to bedrock is the median of driller- and boring-reported depths in the town, shown only where at least 10 logs exist. Water-well logs over-sample rural lots and hilltops; one town median never describes a particular site.
- Bedrock depths use the same state databases and filters as the Bedrock & soils module (bedrock wells and borings that reached rock, 0 < depth ≤ 400 ft, exact re-filings dropped), but every log is placed in a town by its coordinates rather than the driller's town field, so town counts can differ slightly between the two pages. Connecticut and Rhode Island have no statewide public well-log database with depths.
- Dams: only high-hazard-potential dams whose latest condition assessment is Poor or Unsatisfactory are counted (live NID). Connecticut and Rhode Island assessments may lag.
- FEMA Public Assistance dollars are federal share obligated for disasters declared since 2010, reported by county — they are county context, not a town figure.
- Grant awards are Massachusetts only (EEA Dam & Seawall program, MVP Action grants, CZM Coastal Resilience). Other states' programs are not yet included.
- Ground-related permit counts cover only the municipal portals the pipeline reads (Boston, Cambridge, Somerville, Worcester, Framingham, Providence, Portsmouth, Hartford and a few others) — an absent count means 'not covered', not zero.
- Data as of
- Sep 11, 2026
- Generated
- Sep 11, 2026
- Records
- 367,748
- Refresh
- Live pull · weekly
- U.S. Census Bureau cartographic boundary files — county subdivisions (2024, 1:500k)Public domain
- FHWA National Bridge Inventory (2025 delimited files)Public domain
- USACE National Inventory of DamsPublic domainHigh-hazard dams rated Poor or Unsatisfactory (live NID).
- USGS U.S. Landslide InventoryPublic domain
- MassGIS / Massachusetts Geological Survey — Bedrock Data PointsPublic recordBorings and well logs that reached rock (MassDEP well drillers, USGS, MWRA, MassDOT…); seismic/HVSR and map-derived shallow-bedrock/outcrop points excluded.
- NH DES Water Well Inventory, Maine Geological Survey Wells Database, Vermont DEC well recordsPublic recordBedrock wells only; driller-reported depth to bedrock / overburden thickness.
- OpenFEMA Public Assistance Funded Projects Details (v2)Public domain
- MA EEA / CZM grant awards — Dam & Seawall, MVP Action, CZM Coastal ResiliencePublic record
- Municipal open-data permit portals (Boston, Cambridge, Somerville, Providence, Portsmouth, others)Public recordOnly permits flagged as ground-related (retaining walls, excavation, foundations) are counted.
Published by Earth Support Corp as a public resource. Regional statistics for planning and curiosity. They are not an engineering report, a bid recommendation or a statement about any particular site, firm or project. Spot an error? Tell us and we will correct it. Full method: methodology.