[Content] Add the Backward Erosion Piping Screening technical reference to the System Response Library

docs/web-applications/system-response/backward-erosion-piping-screening/v1.0/00-document-info.mdx

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+---
+title: Document Info
+reportDate: October 2026
+reportType: Technical Reference
+reportTitle: Backward Erosion Piping Screening Technical Reference Manual
+reportSubTitle: System Response Library
+reportAuthors: ['Adam Gohs, P.E.']
+reportAbstract: Technical reference documenting the Backward Erosion Piping (BEP) screening model in the System Response library. The model computes a system response probability (SRP) for backward erosion piping at each headwater level using a seven-node event tree. The probability of a continuous foundation flaw is estimated by Bayesian updating of a geology-based prior with subsurface and seepage-observation evidence. Unfiltered-exit and initiation probabilities are computed from blanket theory with a companion defect-survival model for the downstream confining layer, and progression is evaluated with the Schmertmann critical-gradient method. The model applies simplifications appropriate for screening-level risk analysis.
+reportSubjectTerms: ['BEP', 'Backward Erosion Piping', 'Screening', 'Event Tree', 'System Response Probability', 'System Response Curve', 'Blanket Theory', 'Bayesian Updating', 'Schmertmann Method', 'Monte Carlo']
+citationGuide: 'U.S. Army Corps of Engineers, Risk Management Center, <i>Backward Erosion Piping Screening Technical Reference Manual</i>, Lakewood, CO: U.S. Army Corps of Engineers, Risk Management Center, 2026.'
+---
+
+import Link from '@docusaurus/Link';
+import DocumentMetadata from '@site/src/components/DocumentMetadata';
+import NavContainer from '@site/src/components/NavContainer';
+
+<NavContainer
+  link="/web-applications/system-response"
+  linkTitle="System Response Library"
+  document="web-applications/system-response/backward-erosion-piping-screening"
+/>
+
+# Document Information
+
+<DocumentMetadata metadata={frontMatter} />

docs/web-applications/system-response/backward-erosion-piping-screening/v1.0/00-version-history.mdx

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+---
+title: Version History
+---
+
+import NavContainer from '@site/src/components/NavContainer';
+import TableVersionHistory from '@site/src/components/TableVersionHistory';
+
+<NavContainer
+  link="/web-applications/system-response"
+  linkTitle="System Response Library"
+  document="web-applications/system-response/backward-erosion-piping-screening"
+/>
+
+# Version History
+
+<TableVersionHistory
+  versions={['1.0', '1.0', '1.0', '1.0', '1.0', '1.0', '1.0']}
+  dates={['April 2026', 'July 2026', 'August 2026', 'August 2026', 'October 2026', 'October 2026', 'October 2026']}
+  descriptions={[
+    'Initial release.',
+    'Updated for the revised model: Bayesian flaw assessment replaces the qualitative flaw-likelihood selection; the unfiltered-exit node combines a confining-layer defect-survival model with blanket-theory blowout; the blowout and heave analyses route to Blanket Theory Case 2 or Case 4 based on the upstream seepage barrier; the infinite-blanket (full-head) simplification is replaced by finite-blanket head loss with a resolved downstream seepage path; and the input contract is expanded (slope-segment embankment geometry, tri-state confining-layer characterization, upstream blanket, downstream seepage berm, optional tailwater, and multiple embankment materials).',
+    'Updated for revised inputs: the seepage-path lengths (upstream blanket length and the upstream and downstream confining-layer extents) are entered as single values rather than distributions, leaving the unknown-extent default as the only distributional downstream path; the qualitative relative-density categories map to uniform ranges rather than triangular distributions, and a new Custom category accepts a site-specific relative-density distribution; the inert anisotropy-ratio input is removed.',
+    'Updated for the revised berm treatment and reporting: the event-tree effect of a downstream seepage berm now follows where the berm ends relative to the confining layer — a berm ending within a confirmed layer’s known extent retains the through-layer defect and blowout composition at an exit point beyond the berm, while a berm that reaches or clears the layer’s extent (or overlies a confirmed layer of unknown extent) produces a daylighting exit at the berm toe with a certain unfiltered exit and certain initiation. Where the berm toe is itself the daylighting exit, the separate daylight pathway is no longer reported — the toe pathway carries the governing curve — and a separately supplied daylight ground-surface elevation is ignored with a validation warning. The fines-content correction now applies its higher factor at exactly 5% fines and above, and the reported audit record is expanded to cover the resolved analysis configuration, the quantities passed to each delegated analysis, and the rule that produced each composed event-tree node.',
+    'Revised the confining-layer, upstream-extension, relative-density and fines-content inputs so each must be answered, with Unknown a valid answer, and clarified the fines-content correction to the progression method.',
+    'Revised the presentation of the model method for engineering review, with no change to the model or its results.',
+    'Updated for model version 1.1, which changes results: the blowout and heave net head is now measured against the water standing on the confining layer at the toe or berm toe, with the daylight ground setting only the exit level, and a pool below the exit level loads the layer at pool level; beneath a berm within the layer’s known extent, blowout and heave are evaluated at the berm toe; a Very Thin layer uses Blanket Theory Case 4; a berm over a layer of unknown presence makes the berm toe the single exit; and daylight initiation applies only while the pool drives seepage out of the daylighting exit.',
+  ]}
+  modifiedBy={['-', '-', '-', '-', '-', '-', '-']}
+  reviewedBy={['-', '-', '-', '-', '-', '-', '-']}
+  approvedBy={['-', '-', '-', '-', '-', '-', '-']}
+/>

docs/web-applications/system-response/backward-erosion-piping-screening/v1.0/01-preface.mdx

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+---
+title: Preface
+---
+
+import NavContainer from '@site/src/components/NavContainer';
+
+<NavContainer link="/web-applications/system-response" linkTitle="System Response Library" document="web-applications/system-response/backward-erosion-piping-screening" />
+
+# Preface
+
+This document provides a technical reference for the Backward Erosion Piping (BEP) screening model in the System Response library. The model
+computes a system response probability (SRP) as a function of headwater elevation for the backward erosion piping failure mode. It is a screening-level
+model: it applies simplifications intended to reduce input burden while avoiding false negatives, and any application that performs screening-level
+risk analysis can use it.
+
+The intended audience includes dam and levee safety engineers evaluating whether the model is appropriate for their assessment, and peer reviewers
+checking the technical basis of screening-level results. Readers are assumed to have a general background in internal-erosion risk analysis —
+event trees, seepage mechanics, and probability concepts — but no familiarity with the software implementation is required.
+
+The document covers the model's complete execution pathway: the evidence-based assessment of a continuous foundation flaw, the resolution of
+hydraulic loading and seepage-path geometry from the site inputs, the assembly of the seven-node event tree at each pool level, the assumptions
+made along the way with their engineering bases, the inputs the user provides and the options available, and the results the model produces.
+
+## Document Organization
+
+- **[Model Overview](./02-model-overview.mdx)** — The model's purpose and intended use, a summary of its execution pathway from inputs to
+  results, its physics basis, a comparison with the full toolbox models, the exit pathways evaluated and when each exists, and its relationship
+  to the toolbox models.
+- **[Input Parameters](./03-input-parameters.mdx)** — Every user input: hydraulic loading, embankment geometry, upstream blanket, downstream
+  seepage berm, flaw-evidence selections, confining-layer characterization, observed-seepage refinements, embankment materials, foundation sand
+  properties, unit weights, and the intervention and breach probabilities, with units, valid ranges, defaults, and the choices available for
+  each selection.
+- **[Flaw Assessment](./04-flaw-assessment.mdx)** — The Bayesian assessment of the probability that a continuous path of fine to medium, uniform
+  sand exists in the foundation: the geology-based prior, the subsurface-data and seepage-observation evidence updates, and the uncertainty
+  quantification.
+- **[Hydraulic Loading and Seepage Paths](./05-hydraulic-loading-and-seepage-paths.mdx)** — The downstream reference elevations, the treatment of
+  tailwater, the net driving head, the resolution of the upstream, embankment, and downstream seepage path lengths, and the selection between the
+  two blanket-theory configurations.
+- **[Event Tree](./06-event-tree.mdx)** — The seven event-tree nodes, how each probability is populated at each pool level (including the
+  composition of the unfiltered-exit node from the defect and blowout pathways), and how the SRP and the governing system response curve are
+  computed.
+- **[Delegated Methods](./07-delegated-methods.mdx)** — For blanket theory and the Schmertmann progression method: the event-tree node each
+  serves and the question it answers there, the chapter of the dedicated manual that documents it, and each screening-level adjustment.
+- **[Assumptions and Limitations](./08-assumptions-and-limitations.mdx)** — Each modeling assumption with its engineering basis, its effect on
+  results, and the conditions under which it may not hold.
+- **[Output and Interpretation](./09-output-and-interpretation.mdx)** — The results the model produces, how to read the system response curve,
+  how the governing pathway is determined, how key inputs affect the SRP, and the role of screening results relative to detailed analysis.