stormwater-management

name	stormwater-management
description	Skill for integrated stormwater management and green infrastructure design with SWMM modeling, hydrologic analysis, BMP sizing, and MS4 permit compliance.
allowed-tools	Read, Grep, Write, Bash, Edit, Glob
category	Water and Wastewater Treatment
backlog-id	SK-004
metadata	{"author":"babysitter-sdk","version":"1.0.0"}

Stormwater Management Skill

Integrated stormwater management and green infrastructure design for sustainable urban drainage.

Purpose

This skill provides comprehensive capabilities for stormwater management planning, including hydrologic analysis, green infrastructure design, BMP selection and sizing, SWMM modeling, and MS4 permit compliance analysis.

Capabilities

SWMM Modeling and Simulation

• EPA SWMM model setup and configuration
• Subcatchment delineation and parameterization
• Drainage network modeling
• Long-term continuous simulation
• Design storm analysis
• LID representation and modeling

Hydrologic Analysis

• TR-55 methodology implementation
• Rational method calculations
• SCS Curve Number determination
• Time of concentration estimation
• Unit hydrograph development
• Rainfall-runoff modeling

Green Infrastructure Sizing

• Bioretention facility design
• Permeable pavement sizing
• Rain garden design
• Green roof specifications
• Tree box filters
• Vegetated swales

Detention/Retention Pond Design

• Storage volume calculations
• Stage-storage-discharge relationships
• Outlet structure design
• Emergency spillway sizing
• Sediment forebay design
• Maintenance access planning

Water Quality BMP Selection

• Pollutant removal efficiency analysis
• BMP selection matrix
• Treatment train design
• Sizing for TSS removal
• Nutrient removal considerations
• Cost-effectiveness analysis

Pollutant Load Modeling

• Event Mean Concentration (EMC) analysis
• Annual pollutant load estimation
• Source area contribution analysis
• Loading rate calculations
• Reduction target setting

Low Impact Development Integration

• Site-level LID planning
• Watershed-scale LID analysis
• LID retrofit opportunities
• Performance monitoring design
• Adaptive management frameworks

MS4 Permit Compliance Analysis

• NPDES requirements interpretation
• MCM implementation tracking
• TMDL compliance assessment
• Monitoring program design
• Annual report preparation

Prerequisites

Installation

pip install numpy scipy pandas matplotlib

Optional Dependencies

# For SWMM integration
pip install swmm-api pyswmm

# For GIS analysis
pip install geopandas shapely

# For visualization
pip install plotly folium

Usage Patterns

Rational Method Calculations

import numpy as np
from dataclasses import dataclass
from typing import Dict, List, Tuple

@dataclass
class CatchmentData:
    """Catchment characteristics"""
    area_acres: float
    runoff_coefficient: float
    time_of_concentration_min: float
    description: str = ""

class RationalMethod:
    """Rational method for peak runoff calculation"""

    def __init__(self):
        # IDF curve coefficients (example for generic location)
        # Q = C * I * A, where I from IDF: I = a / (Tc + b)^c
        self.idf_coefficients = {
            2: {'a': 100, 'b': 10, 'c': 0.8},
            5: {'a': 120, 'b': 10, 'c': 0.8},
            10: {'a': 140, 'b': 10, 'c': 0.8},
            25: {'a': 160, 'b': , : },
            : {: , : , : },
            : {: , : , : }
        }

     () -> :
        
        coef = .idf_coefficients.get(return_period, .idf_coefficients[])
        intensity = coef[] / (tc_min + coef[]) ** coef[]
         intensity

     () -> :
        
        C = catchment.runoff_coefficient
        I = .rainfall_intensity(catchment.time_of_concentration_min, return_period)
        A = catchment.area_acres

        Q = C * I * A  
         Q

     () -> :
        
        total_area = (a  a, c  subareas)
        weighted_c = (a * c  a, c  subareas) / total_area
         weighted_c


     () -> :
        
        tc =  * (length_ft ** ) * (slope_pct ** -)
         tc


RUNOFF_COEFFICIENTS = {
    : ,
    : ,
    : ,
    : ,
    : ,
    : ,
    : ,
    : ,
    : ,
    : 
}


rational = RationalMethod()


subareas = [
    (, RUNOFF_COEFFICIENTS[]),
    (, RUNOFF_COEFFICIENTS[]),
    (, RUNOFF_COEFFICIENTS[])
]
composite_c = rational.composite_runoff_coefficient(subareas)

catchment = CatchmentData(
    area_acres=,
    runoff_coefficient=composite_c,
    time_of_concentration_min=,
    description=
)

 rp  [, , , ]:
    Q = rational.peak_runoff(catchment, rp)
    ()

SCS Curve Number Method

class SCSMethod:
    """SCS Curve Number method for runoff calculation"""

    def __init__(self, curve_number: float):
        self.cn = curve_number
        self.S = (1000 / curve_number) - 10  # Potential retention (inches)
        self.Ia = 0.2 * self.S  # Initial abstraction

    def runoff_depth(self, rainfall_inches: float) -> float:
        """Calculate runoff depth (inches)"""
        P = rainfall_inches
        if P <= self.Ia:
            return 0.0

        Q = (P - self.Ia) ** 2 / (P - self.Ia + self.S)
        return Q

    def runoff_volume(self, rainfall_inches: float, area_acres: float) -> float:
        """Calculate runoff volume (acre-feet)"""
        Q_inches = self.runoff_depth(rainfall_inches)
        volume_ac_ft = Q_inches / 12 * area_acres
        return volume_ac_ft

    @staticmethod
    def composite_cn(subareas: List[[, ]]) -> :
        
        total_area = (a  a, cn  subareas)
        weighted_cn = (a * cn  a, cn  subareas) / total_area
         weighted_cn


     () -> :
        
         condition == :
            cn = cn_ii / ( -  * cn_ii)
         condition == :
            cn = cn_ii / ( +  * cn_ii)
        :
            cn = cn_ii
         cn


CURVE_NUMBERS = {
    : ,
    : ,
    : ,
    : ,
    : ,
    : ,
    : ,
    : ,
    : ,
    : ,
    : 
}



pre_cn = SCSMethod.composite_cn([
    (, CURVE_NUMBERS[]),
    (, CURVE_NUMBERS[])
])
pre_scs = SCSMethod(pre_cn)


post_cn = SCSMethod.composite_cn([
    (, CURVE_NUMBERS[]),
    (, CURVE_NUMBERS[]),
    (, CURVE_NUMBERS[])
])
post_scs = SCSMethod(post_cn)

rainfall =   
pre_runoff = pre_scs.runoff_volume(rainfall, area_acres=)
post_runoff = post_scs.runoff_volume(rainfall, area_acres=)

()
()
()
()
()

Bioretention Sizing

class BioretentionDesign:
    """Bioretention facility design"""

    def __init__(self, infiltration_rate_in_hr: float = 1.0):
        self.infiltration_rate = infiltration_rate_in_hr

    def size_for_water_quality(self, drainage_area_sf: float,
                                impervious_fraction: float,
                                design_rainfall_in: float = 1.0) -> Dict:
        """Size bioretention for water quality treatment"""
        # Calculate water quality volume (WQv)
        # Using simplified volumetric approach
        Rv = 0.05 + 0.009 * (impervious_fraction * 100)  # Runoff coefficient
        wqv_cf = Rv * design_rainfall_in / 12 * drainage_area_sf

        # Bioretention area sizing
        # Based on 6" ponding depth and filter media depth
        ponding_depth_ft = 0.5  # 6 inches
        drain_time_hr = 24  # Maximum drain time

        # Area based on infiltration during storm
        storm_duration_hr = 2  # Assume 2-hour storm
        infiltrated_depth = self.infiltration_rate * storm_duration_hr / 12  # feet

        # Minimum surface area
        min_area_sf = wqv_cf / (ponding_depth_ft + infiltrated_depth)

        # Typical sizing: 5-10% of impervious area
        recommended_area_sf = drainage_area_sf * impervious_fraction * 

         {
            : wqv_cf,
            : min_area_sf,
            : (min_area_sf, recommended_area_sf),
            : ,
            : ,
            : ponding_depth_ft *  / .infiltration_rate
        }

     () -> :
        
         {
            : surface_area_sf,
            : {
                : ,
                : ,
                : .infiltration_rate
            },
            : {
                : ,
                : ,
                : ,
                : 
            },
            : {
                : ,
                : 
            },
            : {
                : ,
                : [, , ]
            },
            : {
                : ,
                : ,
                : 
            }
        }


bio = BioretentionDesign(infiltration_rate_in_hr=)

sizing = bio.size_for_water_quality(
    drainage_area_sf=,  
    impervious_fraction=,
    design_rainfall_in=
)

()
()
()

details = bio.design_details(sizing[])
()

Pollutant Load Analysis

class PollutantLoading:
    """Stormwater pollutant load estimation"""

    # Event Mean Concentrations (mg/L) by land use
    EMC = {
        'residential': {'TSS': 101, 'TP': 0.38, 'TN': 2.5, 'Zn': 0.14},
        'commercial': {'TSS': 69, 'TP': 0.22, 'TN': 2.2, 'Zn': 0.22},
        'industrial': {'TSS': 85, 'TP': 0.26, 'TN': 2.0, 'Zn': 0.32},
        'highway': {'TSS': 142, 'TP': 0.34, 'TN': 3.2, 'Zn': 0.35},
        'open_space': {'TSS': 40, 'TP': 0.10, 'TN': 1.0, 'Zn': 0.05}
    }

    # BMP removal efficiencies (%)
    BMP_REMOVAL = {
        'bioretention': {'TSS': 85, 'TP': 60, : , : },
        : {: , : , : , : },
        : {: , : , : , : },
        : {: , : , : , : },
        : {: , : , : , : },
        : {: , : , : , : }
    }

     () -> :
        
        emc = .EMC.get(land_use, .EMC[]).get(pollutant, )

        
        
        volume_l = annual_runoff_in *  * area_acres *  *  * 

        
        load_mg = emc * volume_l
        load_lbs = load_mg / 

         load_lbs

     () -> :
        
        efficiency = .BMP_REMOVAL.get(bmp_type, {}).get(pollutant, ) / 
        removed = load_lbs * efficiency
        remaining = load_lbs - removed

         {
            : load_lbs,
            : efficiency * ,
            : removed,
            : remaining
        }


loading = PollutantLoading()


area =   
annual_runoff =   
land_use = 

 pollutant  [, , ]:
    load = loading.annual_load(area, land_use, annual_runoff, pollutant)
    reduction = loading.load_reduction(load, , pollutant)
    (
          )

Usage Guidelines

When to Use This Skill

• Stormwater management plan development
• Green infrastructure design
• BMP selection and sizing
• MS4 permit compliance analysis
• Watershed planning and TMDL implementation

Best Practices

1. Match design storm to local requirements
2. Consider treatment train approaches for multiple benefits
3. Plan for maintenance access in design
4. Verify infiltration rates with field testing
5. Include pre-treatment for high pollutant areas
6. Monitor performance for adaptive management

Process Integration

• WW-004: Stormwater Management Planning (all phases)

Dependencies

• numpy, scipy: Numerical calculations
• pandas: Data analysis
• pyswmm: SWMM model interaction (optional)

References

• EPA SWMM Reference Manual
• ASCE Manual of Practice No. 77
• State-specific stormwater design manuals
• NCHRP Report 565 BMP Selection