Belknap CountyNew Hampshire
Alton, New Hampshire
2 high-hazard dams are rated in poor or unsatisfactory condition. Bedrock sits a median 20 ft down across 1,535 logs, close to the New Hampshire median of 20 ft.
- Live · as of Sep 11, 2026
- 9 public sources · method
- ← All towns
Median depth to bedrock
20 ft
middle half 11–50 ft · 1,535 logs
Bridges rated poor
1
of 10 inventoried
Poor high-hazard dams
2
National Inventory of Dams
FEMA repair $, Belknap County
$3.3M
federal share since 2010 · county-wide
01 · Dams & disasters
2 high-hazard dams need work
FEMA Public Assistance is reported by county, so the figure below is Belknap County-wide context, not a Alton number.
| Dam | Condition | Built |
|---|---|---|
| Sunset Lake DamSuncook River | Poor | 1860 |
| Alton Power DamMerrymeeting River | Poor | 1923 |
High hazard potential means failure would probably cost lives — it rates the consequences, not the dam’s condition.
FEMA Public Assistance, Belknap County
$3.3M
Federal share obligated across 118 projects in 9 declared disasters since 2010. The largest category is roads & bridges (51%); roads & bridges took $1.7M.
02 · Ground
Rock turns up a median 20 ft down
From 1,535 depth-to-rock records inside Alton (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 Alton's logs reach rock between 11 and 50 ft
Depth to bedrock: 10th–90th percentile whisker, middle-half box, median tick; dashed line = New Hampshire median.
median 20 ftNH 20 ft
050 ft
n = 1,535 logsSource: NH DES well inventory
▸ Show the numbers▾ Hide the numbers
| Depth to rock (ft) | Logs |
|---|---|
| 0–5 | 94 |
| 5–10 | 202 |
| 10–20 | 447 |
| 20–50 | 403 |
| 50–100 | 252 |
| 100+ | 137 |
Rock within 10 ft
24%
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. 24% of logs here go past 50 ft.
03 · Bridges
1 of 10 bridges are rated poor — above the New Hampshire rate of 8%
Every highway bridge and large culvert in the 2025 National Bridge Inventory that stands inside Alton. Median age 56 years.
60% good, 10% poor
FHWA good / fair / poor rating — the lowest of deck, superstructure, substructure or culvert.
- Good6 · 60%
- Fair3 · 30%
- Poor1 · 10%
n = 10 structuresSource: FHWA National Bridge Inventory 2025
▸ Show the numbers▾ Hide the numbers
| Built | Structures |
|---|---|
| 1920s | 1 |
| 1930s | 2 |
| 1940s | 2 |
| 1990s | 1 |
| 2000s | 1 |
| 2010s | 2 |
| 2020s | 1 |
The poor-rated bridges
| Carries | Over | Built | Daily traffic |
|---|---|---|---|
| NH 11 | MERRYMEETING RIVER | 1934 | 10,346 |
04 · Next door
Alton and the 10 towns that border it
A dash means no data for that layer, not zero.
| Town | Poor bridges | Rock depth |
|---|---|---|
| Alton, NH | 1 / 10 | 20 ft |
| Gilford, NH | 2 / 19 | 28 ft |
| Barnstead, NH | 0 / 15 | 26 ft |
| Farmington, NH | 4 / 10 | 18 ft |
| Gilmanton, NH | 0 / 7 | 25 ft |
| Wolfeboro, NH | 0 / 6 | 20 ft |
| Tuftonboro, NH | 0 / 6 | 25 ft |
| Meredith, NH | 0 / 4 | 12 ft |
| Moultonborough, NH | 0 / 4 | 15 ft |
| Strafford, NH | 0 / 2 | 16 ft |
| New Durham, NH | 0 / 2 | 20 ft |
Where these numbers come from
Method, sources & caveats
Alton is the Census county subdivision 3300101060 (Belknap 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.