Frequently asked questions

What is the MQPE Locator?

A web tool from Geronimo Engineering for construction stormwater compliance under California’s Construction General Permit (CGP). For a site or an area it shows:

• Measured — past storms whose recorded rainfall met the permit’s Qualifying Precipitation Event threshold, with each event’s 24-hour blocks, hourly rainfall chart and post-event inspection deadline.
• Forecast — whether the current National Weather Service forecast meets the permit’s forecast rule in the coming days.
• Storm replay — a past storm animated across the district hour by hour (see What does Storm replay show?).
• Alerts — email or text alerts for a site or area you choose.
• Data sources — what each rainfall and forecast product is and how current it is.

What is a Qualifying Precipitation Event?

The CGP (Attachment D) defines a Qualifying Precipitation Event (QPE) on the National Weather Service forecast: a 50% or greater chance of rain and 0.5 inch or more forecast over 24 hours.

The tool keeps the NWS forecast only from the time it started archiving it (see Does QPE keep the NWS forecast history?), so the Measured tab applies the same threshold to recorded rainfall and calls the result a Measured Qualifying Precipitation Event (MQPE). An event starts at a wet hour when the next 24 hours total 0.50 inch or more (rounded to the hundredth), continues while each following 24-hour block reaches 0.25 inch, and ends after two blocks in a row below 0.25 inch. The Forecast tab applies the permit’s own forecast rule to the current forecast.

How is the post-event inspection deadline worked out?

It is 96 elapsed hours after the end of the event’s last qualifying 24-hour block (CGP Attachment D). All times are shown in Pacific time; a daylight-saving change inside the 96 hours doesn’t change the deadline, only the clock time it is shown at. Deadlines are per site, so area results don’t show one.

What area does it cover?

Caltrans District 4: Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, Solano and Sonoma counties. A point outside these counties gets an “Outside the covered area” message.

What is a reporting year?

The CGP Annual Report year: July 1 to June 30, named for the year it ends in (reporting year 2026 is July 1, 2025 – June 30, 2026). An event belongs to the year in which it starts, Pacific time. The Measured tab opens on the most recently closed year; the year in progress is marked “in progress — data may be provisional.”

Where does the data come from?

All from public NOAA and state sources:

• NOAA AORC — a gauge-corrected rainfall reanalysis on a 1 km hourly grid. The settled record, but published one calendar year at a time.
• NOAA MRMS — radar rainfall corrected with rain gauges, 1 km hourly, about an hour behind real time. Used for the hours AORC hasn’t published yet.
• Rain gauges — the nearest official station (NOAA GHCN-Daily, or live CDEC and NWS airport gauges where GHCN hasn’t published yet) as a cross-check on each event.
• Forecasts — the National Weather Service forecast (the source the permit names), plus the National Blend of Models (NBM), HRRR, NDFD grids and the California-Nevada River Forecast Center (CNRFC).
• Warnings and atmospheric rivers — active NWS flood warnings, watches and advisories (api.weather.gov), and an atmospheric-river outlook computed from NOAA’s GFS with CW3E’s AR Scale.

The Auto setting (the default) uses AORC wherever NOAA has published it and MRMS for the rest; each result says which it used. The Data sources tab has the details for each.

What does “provisional” mean?

Numbers from near-real-time sources — MRMS and the live gauges — can still be revised as more gauge data arrives, and radar estimates can be less reliable in terrain-blocked coastal areas. Results that use them are labelled provisional. AORC replaces them once NOAA publishes that year.

How current is the data?

• New MRMS rainfall and forecast grids are collected every hour; MRMS runs about an hour behind real time.
• AORC arrives once a year, about 6–9 weeks after each calendar year ends.
• The NWS point forecast is read live from weather.gov when you open the Forecast tab.
• The live radar layer refreshes every 5 minutes; the rain-gauge totals every hour.
• NWS warnings are re-read from weather.gov every 3 minutes while the page is open.
• The atmospheric-river outlook follows each new GFS model run, every 6 hours.

How exact is a result for my site?

Rainfall is read from the grid cell (about 1 km) nearest your point — no interpolation. Each site result shows the cell centre and its distance from your point, and the nearest official gauge’s total for comparison. You can also type your onsite rain gauge total next to an event (it stays in your browser).

Is this an official record? Can I rely on it for compliance?

No. It is a verification and quality-control aid. It does not replace your project’s designated onsite rain gauge or your SWPPP / WPCP as the official compliance record, and it does not reconstruct past National Weather Service forecasts — it shows only those it has archived. Always confirm compliance determinations against your project’s own monitoring records. Alerts support, and do not replace, the forecast monitoring your permit requires.

How do I look up a site?

On the Measured or Forecast tab, choose Point and click the map, search for an address or place, or paste coordinates. Or choose a whole Caltrans district, a county, or Draw on map to outline an area; area results show storm episodes across the area instead of one site. Both tabs share the selection.

Coordinates can be pasted as 37.8771, -122.2486 or in the SWPPP style 37.8771°N 122.2486°W.

My coordinates landed outside the area — “did you mean −122…?”

California longitudes are west, so they are negative. If a longitude was entered without its minus sign (or W), the point lands on the other side of the world, and the tool suggests the same point with the minus sign. Search again with -122… or add W.

What does the site risk level change?

Only the guidance. Set your site’s Risk Level (1, 2 or 3) to tailor the follow-up steps and the Caltrans forms listed: Risk Level 2 adds NAL sampling (pH, turbidity), and Risk Level 3 adds receiving-water monitoring. It does not change which events are found.

How do I save, share or print results?

Measured results and area forecasts have Download CSV; every results view has Print. CSV files and printouts carry the disclaimer and the data provenance. The address bar always holds the current view, so you can copy it to share exactly what you are looking at.

What does the Forecast tab show?

The forecast for the next several days in 6-hour steps, with the permit’s forecast QPE rule applied: a 50% or greater chance of rain and 0.50 inch or more over four 6-hour intervals. If a QPE is forecast, it shows when it starts and ends, the pre-storm inspection window, and what the permit requires now.

For a point the default is the NWS forecast, the one the permit names; Conservative takes the highest value from every available forecast. Area outlooks use gridded forecasts (NBM by default). For monitored sites you can also see what an archived forecast said, from September 2026 onward (Issuance → History); the Measured tab’s event reports use the archived NWS forecast grid, which covers every point (see Does QPE keep the NWS forecast history?).

Does QPE keep the NWS forecast history?

Yes, for all of Caltrans District 4. Every hour the tool collects the National Weather Service’s National Digital Forecast Database (NDFD) — the gridded forecast that forecast.weather.gov point forecasts come from — and keeps every cycle: the 6-hour rainfall amounts (QPF, days 1–3) and the 12-hour chance of rain (PoP, days 1–7) on NDFD’s 2.5 km grid. Older cycles can be added from NOAA’s own NDFD archives, which are online back to mid-2018. The first and last archived cycle, and any gaps, are in the archive index the tool publishes.

For each measured event, the event detail’s lead-up step uses that history to say when the NWS forecast first showed a 50% or greater chance of rain and 0.50 inch or more in 24 hours for that storm (and the Caltrans 0.10 inch pre-storm trigger), the pre-storm inspection window that implies (72–120 hours before the forecast storm start), and a small chart of what each forecast cycle said as the storm approached. A forecast storm counts as the measured event when its forecast start is within 72 hours before the measured start or during the event. The CSV download carries the same dates, and the list of events notes storms the forecast missed and forecast QPEs that did not materialise (no measured event within that window). Events older than the archive, or inside a stretch it has no forecast cycles for yet (a gap while older months are still being filled in), say so instead.

This is separate from the Forecast tab’s Issuance → History, which keeps the full point forecast (api.weather.gov, and the other forecast sources) for monitored sites from September 2026. Both come from the same NWS forecast — api.weather.gov point forecasts are drawn from the NDFD grid — but only the grid covers every point, so the Measured tab uses it. Nothing is collected twice: the grid is the same one the Forecast tab’s area outlook already reads, now kept instead of deleted after two days.

Caveats: the values are for the 2.5 km grid cell holding the point, not the exact point; NWS can update the forecast between the hourly cycles the tool collects, so a short-lived update may be missing; and a gap in the archive (the collection briefly down) can make the first date later than the NWS actually showed it. Your weather-monitoring log (file 20.40) remains the record of what was observed on site.

What do the 3D and Storm 3D views show?

3D tilts the map and shows terrain with hillshading, from public elevation tiles. The terrain height can be exaggerated up to three times so hills read clearly.

Storm 3D draws the selected storm’s total rainfall as a column on each ~1 km cell — colour and height both show depth. Heights are exaggerated for readability (adjustable), and traces under 0.1 inch aren’t drawn. Drag with the right mouse button, Ctrl-drag, or use two fingers to tilt and turn.

What does Storm replay show?

Storm replay animates a past storm across District 4 hour by hour, from the same hourly NOAA rainfall grids (AORC, then MRMS radar after AORC’s last hour) the rest of the tool reads. Pick one of the largest recent storms or any window up to 4 months (122 days), then switch between five views. Windows longer than 3 weeks (1 week on low-memory devices) play 6-hour or daily totals, added up from the hourly values — Threshold watch still tests every hour’s trailing 24-hour total — and “Hour by hour” opens any 3 weeks of them; radar plays for windows of 14 days or less:

• Rain intensity — each hour’s rain rate in inches per hour, blending smoothly between hours.
• Accumulation — the storm total so far; in 3D it rises as columns, coloured and sized like Storm 3D.
• Falling rain — drops that fall faster and denser where it rained harder. For the eye only.
• Storm track — where the heaviest rain was each hour.
• Threshold watch — each cell lights up the hour its trailing 24-hour total first reaches 0.50 inch, with the area of the district over that line. It’s a picture of the storm, not an event finding: the Measured tab applies the permit’s 24-hour blocks.

Hover or tap a cell for its numbers, and use Share this replay for a link to the same storm, view and hour. It all runs in your browser: your device downloads the published rainfall files (a few megabytes per storm) and decodes and animates them itself — no server computes anything. Space plays and pauses; the arrow keys step an hour. With reduced motion turned on in your device settings, playback steps whole hours and the drops hold still.

What are the storm summaries, and how are storms named?

Storm summaries are one page per District 4 storm that put at least 0.5 inch of rain into a 24-hour block somewhere in the district: how much of the district crossed, where it rained most, the Caltrans projects and CGP sites that had an MQPE, and the gauges. They are provisional (MRMS radar estimates) until NOAA’s AORC reanalysis covers the dates, then final.

Each storm has a date address (/storms/2026-02-14, its first Pacific date) and a name, made by fixed rules: the part of the month it began in (“Early”, “Mid-” or “Late”), or a well-known holiday it spans (New Year’s, MLK Day, Valentine’s Day, Presidents’ Day, Easter, Thanksgiving, Christmas); then “atmospheric river” when QPE’s own AR outlook record had AR 1 or stronger on the CW3E scale during the storm, otherwise “storm” (storms from before that record began are all “storm”). A second storm with the same name becomes “…, second storm”. A name is given once and never changed — not when the storm turns final, not when its numbers move. The name also works as an address (/storms/mid-december-2025-storm).

Storm pages are permanent

Once a storm page is published, its address keeps working. When AORC replaces the radar estimates, the page keeps its address and name and its numbers update. If newer data joins two storms into one, the later page forwards to the storm it joined (its old name still leads there too); if a storm turns out not to have crossed the threshold after all, its page stays and says so. Pages and their maps are only ever overwritten, never deleted, and the sitemap lists each storm once, at its own address.

What is “Storms at this project / site” on a project or site card?

Every published storm that put an MQPE on that Caltrans project or CGP site, by the same rule the storm pages count with (a project: the highway 300 m either side of it, 750 m around its middle; a site: its nearest rain cell): when its first 24-hour block over 0.5 inch began, the largest 24-hour total and the storm total there, with links to the storm page and to Storm replay focused on it, and a CSV download. It is the radar-based record — the site’s own rain gauge remains the record of compliance — and it is matched against the project and site lists current when each storm was computed, so older storms are approximate.

What is the live radar layer?

The Live radar button overlays the NEXRAD radar composite from the Iowa Environmental Mesonet, refreshed every 5 minutes. It shows where it is raining now — situational awareness only, never a compliance number.

What are the NWS warnings on the map?

The National Weather Service’s active flood products for District 4 — Flash Flood and Flood Warnings, Flood and Flash Flood Watches, Flood Advisories, flood statements, the Hydrologic Outlook and debris-flow statements — read by your browser straight from NWS (api.weather.gov) when the page opens and every 3 minutes while it is on screen. High wind, winter storm and coastal flood products can be added from the list. When any is active, a pill at the top right of the map says how many; click it for the list, and an alert for its card: what NWS says, when it is in effect (Pacific time), the areas, what to do and a link to the full text on weather.gov. Red solid outlines are warnings, blue dashed are watches, amber dotted are advisories and outlooks; each also carries its name and icon.

A storm-based warning is drawn with the polygon NWS issued; a watch or outlook that names whole forecast zones or counties is drawn with those outlines. When your site or a Caltrans project lies inside an active alert, its results say so (“Flash Flood Warning in effect here until 4 PM”).

Official warnings are the National Weather Service’s — always follow NWS and local officials. This layer only repeats them; if it can’t reach NWS it says so, and weather.gov is the place to check.

What is the atmospheric-river outlook on the Forecast tab?

Atmospheric rivers (ARs) are long, narrow bands of Pacific water vapour that bring most of the Bay Area’s heavy rain. The Center for Western Weather and Water Extremes (CW3E, Scripps / UC San Diego) ranks them from AR 1 (weak, primarily beneficial) to AR 5 (exceptional, primarily hazardous) by how much vapour they carry and how long they last at a place (Ralph et al. 2019).

The card at the top of the Forecast tab is QPE’s own calculation with CW3E’s published method: the vapour transport forecast by NOAA’s GFS model at four coastal points from Santa Cruz to the Sonoma coast, every 3 hours for 7 days, refreshed with each new GFS run (every 6 hours). It is not a CW3E product — CW3E publishes its own ensemble AR Scale forecasts as images at cw3e.ucsd.edu/arscale, which the card links to.

An AR tells you a big storm is coming days ahead; it doesn’t decide the permit. Whether there is a forecast QPE at your site is still worked out from the NWS forecast below the card. Situational awareness only — official watches and warnings come from NWS.

What are the rain gauges on the map?

The Rain gauges button shows how much rain public gauges measured over the last 24 hours, 72 hours, 7 days or the reporting year so far. Bigger, darker dots mean more rain; a hollow grey mark means the gauge missed too much of the window to give a total. The marker’s shape tells the kind of network — circles for state and federal networks (CDEC), squares for airports, triangles for the county flood-control networks, diamonds for CoCoRaHS volunteers — and the chips in the layer’s card switch each network on or off.

Click a gauge for its totals, its last 7 days hour by hour, the rain events in them, a link to download its whole hourly record as CSV, and its station page. Gauges are a cross-check: the MQPE result for your site still comes from the gridded NOAA rainfall at that point.

Which rain gauges does the tool keep, and how often?

Every public rain gauge in District 4 and within about 10 km (6 miles) of it, archived hour by hour and kept:

• CDEC (California Department of Water Resources) — state, federal and local gauges that report to CDEC, including CAL FIRE / BLM weather stations (RAWS), all of Contra Costa County Flood Control’s gauges, the Solano County Water Agency, SFPUC and Zone 7.
• Airports — NWS / FAA ASOS and AWOS stations (hourly weather reports, via the Iowa Environmental Mesonet).
• County flood-control networks — Santa Clara Valley Water, Napa County, Sonoma Water, San Mateo County (OneShoreline) and Marin County. These dense ALERT networks report each tip of the bucket as it happens.
• CoCoRaHS — volunteers’ daily readings, taken about 7 a.m. Daily only, so they are kept apart from the hourly record and never mixed into hourly totals.

The archive is updated every hour and re-reads the last three days each time, so late reports and the agencies’ own corrections are picked up. Every value is stored as the rain in one clock hour (UTC), with when it was fetched and what the source originally reported. Alameda County’s own flood-control gauges, SFPUC’s private network and commercial weather networks are not public and are not included.

How are gauge readings checked?

Each hour is checked automatically. A negative value, or more than 3 inches in one hour (15 inches in a CoCoRaHS day), is rejected — the original number is kept but not used. Other hours are marked as suspect but kept: the same non-zero value six or more hours in a row (a stuck sensor), an hour of an inch or more with dry hours all around it, an hour with fewer reports than the gauge normally sends, and an hour where a running total was reset. Gauges that only report when it rains are assumed dry between reports while their regular check-in signal still arrives; after a day and a half of silence their hours count as missing.

Flagged hours are marked in each gauge’s chart and listed in its CSV, and totals skip rejected hours. A window with more than a fifth of its hours missing has no total.

Why doesn’t the nearest gauge match the radar total?

A gauge measures the rain that fell into one small funnel; the radar-based grid gives the average over a cell about a kilometre across. In showers the two can differ a lot even a short walk apart, and gauges have their own errors (wind, blockages, missed tips). The point results show the nearest hourly gauge’s total for each event next to the grid total — “Radar 0.93 in · nearest gauge (SCVWD #6034, 1.2 km) 1.05 in” — as a sanity check, not a replacement. Your project’s onsite gauge remains the record for your site.

What is the Stream sensors layer?

The Stream sensors button shows stream, river, reservoir and water-quality monitoring sites in District 4 and within about 15 miles of it, taken from the open map of geronimo-iot, a separate environmental-monitoring platform run alongside this tool. Each of its layers has its own switch, with geronimo-iot’s own name and description: Sensors on this platform (sensors whose owners chose to list them publicly), USGS gauges (coloured by how today’s flow compares with the gauge’s record), CDEC (California DWR) (station type shown by marker shape), NWS river gauges (coloured by flood category), Monitor My Watershed community sites, and Reclamation and Army Corps sites. CDEC rain gauges start switched off here — their rain totals are in the Rain gauges layer.

Water quality stations only (on by default) keeps the sites that report at least one water-quality parameter: water temperature, specific conductance, dissolved oxygen, pH, turbidity, nutrients, chlorophyll, salinity, ORP or fDOM. Flow, stage, storage, rain, snow and air measurements alone don’t count. A site’s parameters come from its network: USGS series that reported in the last 30 days (USGS’s own data service), CDEC, Reclamation and Army Corps sensor lists, and the instruments of geronimo-iot’s own sensors.

Shape tells the network (and CDEC’s station type); a hollow marker hasn’t reported lately and a slashed one is offline or out of service. Point at a site for its latest readings — water quality first. Click it for the last 7 days: one small chart per variable it reports (water quality first), with its unit, latest, low and high, gaps where the readings stopped, times in Pacific, and a crosshair readout (point, tap or drag — or focus a chart and use the arrow keys). Show as table lists every reading; Expand opens the same charts larger. The card’s Open these 7 days in geronimo-iot analytics link opens the same week on geronimo-iot’s analytics page, where you can widen it to any date range and export CSV.

The charts come from each network’s own public service: USGS, NWS, Reclamation and the Army Corps straight from the agency; geronimo-iot’s own sensors, CDEC and Monitor My Watershed through geronimo-iot (which limits how often it relays those, so a busy hour can show “the relay is busy — try later”). Readings refresh every 5 minutes while the layer is on (charts: each time you open a site, kept for 15 minutes); they are provisional monitoring data from their owners, not part of the MQPE calculation.

CEDEN samples (a test-tube marker, its own switch) are water-quality samples from the California Environmental Data Exchange Network — the State Water Board’s exchange for monitoring programs (stormwater permittees, irrigated-lands coalitions, SWAMP, beach and creek groups) — as published on data.ca.gov: every station in District 4 and within about 15 miles with a result in the current water year or the five before it. These are grab samples, not continuous sensors: someone took a bottle or a field reading on the day shown. A station’s card lists its program, the days it was sampled and the parameters measured (turbidity / TSS, pH, temperature, dissolved oxygen, conductivity, nutrients, bacteria, metals, pesticides, toxicity tests and others); click it for one dot chart per field and conventional parameter (turbidity, TSS, pH, temperature, DO, conductivity, nitrate, E. coli, fecal coliform). A hollow dot was not detected and is drawn at the reporting limit; a ringed dot is a sample CEDEN marks as storm runoff, and a dashed ring marks a sample taken on a day with at least 0.5 in of rain at the station by this site’s QPE (the same published rainfall the Point tool reads). Results CEDEN marks as rejected, blanks, spikes, duplicates and lab QC recoveries are left out; estimated or qualified results are kept and say so. Every CEDEN station counts as a water-quality station; stations not sampled in the last few years (5 by default — your choice) are drawn hollow, or hidden. The CEDEN files are rebuilt weekly from data.ca.gov, which the Water Board refreshes about monthly.

What is the Caltrans projects layer?

The Caltrans projects button maps District 4 highway projects. Under construction: every active District 4 contract in Caltrans’ monthly Statement of Ongoing Contracts (checked weekly for a new edition), together with Caltrans’ construction map (checked every two days), which shows most but not all of them. Upcoming or advertised contracts come from the Caltrans Contracting Opportunities Portal (checked weekly). The legend says which edition of the statement the layer covers and how many contracts it lists. Search above the map by EA (e.g. 04-0AA194), route (“SR 37”, “I-80”), county, contractor or words of the description, or click a project for its details and source links.

A project’s card shows the statement’s contract figures — current and original contract amount, payments to date, percent of work complete, working days and contract dates — labelled with the edition they come from (“SOC, September 2026”) and linked to Caltrans’ document. Payments are through the edition’s progress-estimate date, so they trail the work by up to about a month.

Where Caltrans publishes a project’s route and postmile limits, it is drawn along the highway from Caltrans’ postmile data; otherwise it is a single postmile, or — marked “location approximate”, hollow on the map — Caltrans’ own marker, which Caltrans says is approximate. Contracts the statement lists at “various locations” (or with no postmile) have no place on the map: they are in search and the counts, not drawn. Completed projects (gone from the construction map or the statement, or accepted) stay on the map, faded, for 90 days. Signed in, “Set rain alerts for this project” opens a new alert for the highway 300 m either side of the project, widened to 750 m around its middle so at least one 1-km rain-grid cell is inside (or its point): the usual forecast QPE, measured QPE with its inspection deadline, and all-clear alerts.

What are CGP sites on the map?

The CGP sites button maps every construction site in District 4 covered by California’s Construction General Permit — each one has a WDID (Waste Discharge Identification number) from the State Water Resources Control Board. Active permits are shown, plus permits whose Notice of Termination took effect in the last 90 days (hollow, “completed”). A square marker is a Risk Level (the number on it), a diamond a Linear Underground/Overhead Project type, a circle a permit that states neither. The legend filters by risk, status and disturbed acreage; the search above the map finds a site by WDID, site name, address or city (alongside Caltrans projects — each result says which it is).

The data is the Water Board’s SMARTS database as the Board publishes it on the California Open Data Portal (“Construction Discharge – Facility Information”), which the Board refreshes weekly; this tool reads it once a week. A site is in District 4 when its filed latitude/longitude is inside one of the nine counties (or, with no usable coordinates, when the permit names one of them); coordinates are used as filed, fixed only when the latitude and longitude were obviously swapped or the minus sign was missing, and flagged as approximate when filed to two decimals or fewer. When a site is clearly the same work as a Caltrans project — its site name gives the project’s EA — its card says “Also a Caltrans project”.

Privacy: only facts about the site are used — WDID, site name and address, county, location, risk level, status and dates, and disturbed acreage. The permit’s owner, developer, contact, QSD and certifier names, addresses, phone numbers and emails are dropped when the data is read and never stored or shown here.

This is a convenience copy. The official record is SMARTS (smarts.waterboards.ca.gov → “Storm Water Data Public Access”), which can be newer than the weekly copy. Signed in, “Set rain alerts for this site” opens a new point alert at the site, named with its WDID, with the permit’s risk level already chosen.

What is “SMARTS filings” on a CGP site card?

Signed in, a CGP site’s card shows, for each reporting year, what the site reported to the State Water Board in SMARTS next to what QPE measured there: the ad hoc sampling events filed (precipitation, dewatering and non-storm water events, with their dates), the days whose average effluent pH or turbidity is outside the permit’s Numeric Action Levels (pH 6.5–8.5, turbidity 250 NTU — the value and the NAL side by side), and a line “QPE measured N MQPE storms here; M of them overlap a reported sampling event” (naming those storms): of the storms in the site’s storm history that year, how many have a filed sampling event within a day of the storm. A fold lists the Water Board’s own violation and enforcement records for the WDID, by type and date only.

How to read it: it is a side-by-side view, not a compliance finding. Not every MQPE requires sampling — Risk Level 1 sites don’t sample, and sampling depends on the site actually discharging — so a storm without a sampling event is expected at many sites. Results the data shows as impossible (a pH above 14, say) are left out and counted. Filings can reach SMARTS weeks later.

Source and refresh: the Board’s SMARTS data on the California Open Data Portal (“Construction Discharge – Monitoring Data”, “Violations”, “Enforcement Actions”), read once a week for the District 4 sites on the map; each section says the date of the data. Annual Reports aren’t in the open data: their status appears only after a SMARTS Annual Reports download has been imported, and otherwise the card says so. The official record is SMARTS — search it for the site’s WDID.

Privacy: only facts about the site and its reports are kept — WDID, report IDs, reporting year, event and sample dates, parameter, value, unit, the NAL, and the type and date of a Board record. The QSP and certifier names, monitoring-location descriptions, the Board’s narrative text and any contact details in the source are dropped when the data is read and never stored or shown.

What is the Receiving waters layer, and the “Drains to / Impaired for” section?

The Receiving waters button maps the impaired waters in and within 10 km of District 4: streams, bays and lakes on California’s 303(d) list — the State Water Board’s 2024 California Integrated Report, the newest list USEPA has approved (December 13, 2024). Each is coloured by its first listed pollutant group of sediment / turbidity, nutrients and bacteria (grey: other pollutants only), and its line shows its TMDL status: solid where a TMDL is still required, dashed where a USEPA-approved TMDL is in place, dotted where another action addresses it. The Impaired for menu shows only the waters listed for one group (metals, pesticides, toxicity, temperature, trash…). Zoomed in, the dashed grey lines are USGS HUC-12 subwatersheds; hatched areas on the coast are Areas of Special Biological Significance (ASBS), where the California Ocean Plan prohibits waste discharges. Click a water for its listed pollutants, each one’s TMDL (name and approval date) or expected TMDL date, and a link to the State Water Board’s fact sheet.

A point’s results, and each Caltrans project’s card, have a Drains to / Impaired for section. It finds the point’s HUC-12 (for a project: its ends and middle), follows the USGS Watershed Boundary Dataset’s downstream routing to the bay or the ocean, and lists the 303(d) waters on that path, nearest first: every listed water in the point’s own HUC-12, then further down only the waters that carry the flow on and the bays, estuaries and tidal wetlands that receive it. It names the pollutant groups, says which have a completed TMDL, and adds a plain-language line for each (for example, a sediment TMDL downstream likely puts sediment on your permit’s Attachment H list, and turbidity readings matter more). It flags an ASBS on the path or within 2 km. The sampling step of an event’s report repeats the pollutants it found.

Screening only — confirm receiving waters in your SWPPP. HUC-12s are drawn at roughly 90 m detail and the path follows whole subwatersheds, not storm drains or the actual outfall, so it can list a water your site doesn’t reach or miss one it does. It is not a determination of your permit’s requirements. The data is refreshed monthly (the list changes once per two-year cycle): the 303(d) list and the Integrated Report’s map layers from the State Water Board, HUC-12s from USGS (The National Map), and ASBS from the State Water Board (2005 Ocean Plan boundaries, which the Board says are for mapping and illustrative purposes only). When USEPA approves the 2026 list, the layer moves to it.

Can I install it as an app?

Yes — it installs straight from the browser, no app store. It then opens in its own window (full screen on a phone) from your home screen, dock or Start menu, and starts faster because the app itself is kept on the device. Rainfall data, forecasts and alerts still come live from the internet each time; offline the app still opens from its saved copy and says you’re offline.

• Android, Chrome or Edge on a computer: use Install app at the top right (it appears once the browser offers it), or the browser menu’s Install / Add to Home screen.
• iPhone and iPad: tap Share → Add to Home Screen (Install app at the top right shows how).

Updates arrive by themselves: when a new version is ready the app offers Reload to update.

Do I need an account?

Not to use the map and results. An account is only needed to set up alerts. Creating one confirms your email address with an emailed code. There are no passwords.

How do I sign in?

Enter your email address and we email you a 6-digit code. Enter the code to sign in.

What alerts are there?

• Forecast QPE — the forecast meets the permit’s forecast QPE rule; the pre-storm inspection window opens.
• Measured event (MQPE), from provisional MRMS data, in up to three messages per storm: in progress once measured rain reaches 0.50 in in 24 hours, with the earliest the post-storm inspection can fall due; likely ended once a following 24 hours stays below 0.25 in, with the deadline and follow-up steps for your risk level (sent again if rain resumes and moves the end later); and confirmed after a second such 24 hours. An event only ends after two dry 24-hour blocks, so confirmation comes about two days after the event end; the earlier messages are there so you are not waiting on it. Measured-event messages are for point alerts; area alerts send the confirmation only.
• Deadline reminder — the day before a post-storm inspection is due.
• Downgrade / all clear — a forecast QPE no longer meets the rule in the latest forecast.
• NWS flood warning (optional) — the National Weather Service issues a Flash Flood or Flood Warning that covers your site or area; checked every few minutes, one message per warning however often NWS updates it. NWS’s warning is the official one — follow NWS and local officials.

Choose As it happens, or a Daily digest that bundles them into one message at 7 AM Pacific (deadline reminders and NWS warnings are never held for the digest). A site alert reads the NWS forecast; an area alert reads the NBM outlook and fires when any part of the area qualifies, giving the wettest total and the share of the area. The alert form shows a preview of each message.

Can I send alerts to other people?

Yes — add their email address or mobile number to an alert. Nothing is sent to them until they confirm with the link we send.

How do I stop alerts or delete my account?

• Texts: reply STOP to any message to stop all alert texts to that number; reply START to turn them back on, or HELP for help.
• Email: use the unsubscribe link in any alert email.
• In the app: pause or delete an alert, or remove a contact from it.
• To delete your account and everything in it, email [email protected].

How often will I get texts, and do they cost anything?

It depends on the weather and your alerts — none in a dry week, several a day during a storm. Message and data rates from your carrier may apply. See the SMS Terms.

Why didn’t I get a code or an alert?

• Check spam or junk folders for email.
• If you ever replied STOP to our texts, nothing more is sent to that number until you reply START.
• Code requests are limited, so after several tries wait a while before asking again.
• Alerts only go out when the forecast or measured data actually meets the alert’s rule.
• Still stuck? Email [email protected] and say which address or number you used.

What do you do with my information?

See the Privacy Policy and the SMS Terms. We don’t show ads and don’t sell or share personal information for marketing.

Who runs this, and how do I get help?

The MQPE Locator is run by Geronimo Engineering. Questions, problems or corrections: email [email protected].