Hillsborough CountyNew Hampshire
Manchester, New Hampshire
2 high-hazard dams are rated in poor or unsatisfactory condition. 4 of its 81 inventoried bridges are rated poor (5%, against 8% statewide).
- Live · as of Sep 11, 2026
- 9 public sources · method
- ← All towns
Median depth to bedrock
15 ft
middle half 8–25 ft · 169 logs
Bridges rated poor
4
of 81 inventoried
Poor high-hazard dams
2
National Inventory of Dams
FEMA repair $, Hillsborough County
$39.7M
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 Hillsborough County-wide context, not a Manchester number.
| Dam | Condition | Built |
|---|---|---|
| Kelley Falls DamSuncook River | Poor | 1830 |
| Dorrs Pond DamDorrs Pond | Poor | 1934 |
High hazard potential means failure would probably cost lives — it rates the consequences, not the dam’s condition.
FEMA Public Assistance, Hillsborough County
$39.7M
Federal share obligated across 415 projects in 10 declared disasters since 2010. The largest category is emergency protective measures (90%); roads & bridges took $1.8M.
02 · Bridges
4 of 81 bridges are rated poor — below the New Hampshire rate of 8%
Every highway bridge and large culvert in the 2025 National Bridge Inventory that stands inside Manchester. Median age 64 years.
49% good, 5% poor
FHWA good / fair / poor rating — the lowest of deck, superstructure, substructure or culvert.
- Good40 · 49%
- Fair37 · 46%
- Poor4 · 5%
Structures by decade built
n = 81 structuresSource: FHWA National Bridge Inventory 2025
▸ Show the numbers▾ Hide the numbers
| Built | Structures |
|---|---|
| pre-1910 | 3 |
| 1910s | 2 |
| 1920s | 1 |
| 1930s | 1 |
| 1940s | 1 |
| 1950s | 11 |
| 1960s | 23 |
| 1970s | 17 |
| 1980s | 7 |
| 1990s | 2 |
| 2000s | 5 |
| 2010s | 7 |
| 2020s | 1 |
The poor-rated bridges
| Carries | Over | Built | Daily traffic |
|---|---|---|---|
| I-293 FEE TPK | STARK WAY | 1956 | 46,106 |
| I-293 NH 3A TPK N | BLACK BROOK | 1956 | 24,101 |
| I-293 NH 3A TPK S | BLACK BROOK | 1956 | 22,005 |
| SALMON STREET EB | MERRIMACK R CSX RD RAMP | 1970 | 13,150 |
03 · Ground
Rock turns up a median 15 ft down
From 169 depth-to-rock records inside Manchester (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 Manchester's logs reach rock between 8 and 25 ft
Depth to bedrock: 10th–90th percentile whisker, middle-half box, median tick; dashed line = New Hampshire median.
median 15 ftNH 20 ft
02040 ft
n = 169 logsSource: NH DES well inventory
▸ Show the numbers▾ Hide the numbers
| Depth to rock (ft) | Logs |
|---|---|
| 0–5 | 18 |
| 5–10 | 34 |
| 10–20 | 59 |
| 20–50 | 46 |
| 50–100 | 11 |
| 100+ | 1 |
Rock within 10 ft
36%
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. 7% of logs here go past 50 ft.
04 · Next door
Manchester and the 7 towns that border it
A dash means no data for that layer, not zero.
| Town | Poor bridges | Rock depth |
|---|---|---|
| Manchester, NH | 4 / 81 | 15 ft |
| Bedford, NH | 2 / 23 | 12 ft |
| Merrimack, NH | 2 / 18 | 17 ft |
| Londonderry, NH | 1 / 17 | 12 ft |
| Hooksett, NH | 0 / 15 | 12 ft |
| Auburn, NH | 1 / 10 | 10 ft |
| Goffstown, NH | 1 / 8 | 12 ft |
| Litchfield, NH | 0 / 1 | 36 ft |
Where these numbers come from
Method, sources & caveats
Manchester is the Census county subdivision 3301145140 (Hillsborough 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.