# Presentation: 665626

## New Hampshire Nutrient Lake TMDLs Medium Scale Complexity Models 

- New Hampshire Nutrient Lake TMDLs Medium Scale Complexity Models

- Sarah MacDougall & Don Kretchmer

## Total Maximum Daily Loads

- TMDLs
- Required for Impaired Waters
- Watershed Loading Study
- Maximum Pollutant Load
- TMDL= WLA + LA + MOS

## Modeling for TMDLs

- Simulate complex watershed processes
- Scope problems
- Set targets
- Evaluate management options

## Model Types

- Mass Balance
- Input/output Vollenweider
-     Equation

- Simple

- Complex

- HSPF-BASINS
- SWAT
- WASP/EUTRO5
- WQRRS
- BIOLA
- SNL-EFDC

- AVGWLF- land use export only
- Sparrow – land use export only
- Reckhow’s NE lakes model
- P8 - Bathtub, Flux, Profile
- WiLMS
- ENSR-LRM

- Medium Scale

## Part I:ENSR-LRM Watershed

- What it does
- Uses “local” nutrient export coefficients
- Allows sub watershed analysis
- Uses attenuation factors to calibrate results to tributary data

- What it does not do
- Storm specific dynamics
- Fate and Transport

- Excel spreadsheet based export coefficient model

## Part II:ENSR-LRM In-Lake Model

- What it does
- Calculates
-  Total Phosphorus
- Chlorophyll *a*
- Secchi Disk Transparency
- Probability of algal bloom
- Allows seasonal assessment
- Calibrates results with in-lake data

- What it doesn’t do
- Multi-dimensional modeling
- Mechanistic modeling
- Stochastic probability modeling

- Combines export coefficient model with empirical in-lake models

**Notes:**
Stochiastic modeling- Monte Carlo Simulations

## Application	 of ENSR-LRM

- 30 NH nutrient impaired lakes
- Chlorophyll *a*
- Cyanobacteria
- Dissolved Oxygen
- Modeled Total Phosphorus (TP)

- Algal Bloom

## GIS Land use

**Watershed Phosphorus & Hydrologic Loads**

**In Lake TP**

**Internal TP Recycling**

**Water Fowl**

**Septic Systems**

**Mean Chlorophyll *****a***

**Probability of Algal Bloom**

**Atmospheric**

**Direct Phosphorus Loads**

**Mean Secchi Disk**

**Point Source**

## Hydrologic Loading Calculation

- Input average annual precipitation
- Determine runoff/base flow fractions for each land use
- Reality Check
- Check load against standard water yield
- Calibrate using attenuation factors

**Notes:**
More specifically, the hydrologic load is calculated by

## TP Loading Calculations

- Point sources
- Nonpoint sources
- Watershed loading
- Septic system
- Water fowl
- Atmospheric
- Internal

## Watershed TP Loading	

- Add GIS land use data

## Coefficient Look up Tables 

- Coefficient Look up Tables

## Septic System TP Load 	

- Harvey Lake, Northwood
- Counted # of dwellings in 125 ft lake buffer
- Used reference export P coefficients & water use, attenuation factors
- Calculated septic loads
- Seasonal single family
- Year-round single family
- Coe Brown School

## Water Fowl TP Load

- Greenwood Pond, Kingston
- Input average annual bird population
- Multiply by export coefficient for water fowl

## Atmospheric TP Load

- Showell Pond, Sandown
- Input area of lake
- Multiply by export coefficient
- Precipitation
- Dust from gravel operation

## Internal TP Load

- Pawtuckaway Lake, Nottingham
- Input volume of anoxic zone
- Calculate P load using hypolimnetic P accumulation over summer

**Fish Kill**

## GIS Land use

**Watershed Phosphorus & Hydrologic Loads**

**In Lake TP**

**Internal TP Recycling**

**Water Fowl**

**Septic Systems**

**Mean Chlorophyll *****a***

**Probability of Algal Bloom**

**Atmospheric**

**Direct Phosphorus Loads**

**Mean Secchi Disk**

**Point Source**

## In-Lake TP Predictions

**Reality check (monitoring data)**

**Notes:**
There is a lot in this table.  I just want to get across that the inlake TP is calculated using 6 empirical equations including Mass Balance.  Any number of these equations can be used, but we usually take the average of the last 5 equations.  The difference in the equations is how they deal with P retention and settling.  The concentration is checked against the historical monitoring data.

Some more sophisticated models use the same equations.

## GIS Land use

**Watershed Phosphorus & Hydrologic Loads**

**In Lake TP**

**Internal TP Recycling**

**Water Fowl**

**Septic Systems**

**Mean Chlorophyll *****a***

**Probability of Algal Bloom**

**Atmospheric**

**Direct Phosphorus Loads**

**Mean Secchi Disk**

**Point Source**

## TMDL Procedure with ENSR-LRM

- Model current scenario
- Calibrate to available observed data
- Model background conditions
- Set watershed back to forest & wetlands
- Model max practical reduction
- Model load required to meet TP target criteria
- Determine Load Allocation      (nonpoint source)
- Determine Waste Load Allocation (point source)
- Estimate percent reduction required

## Advantages of                      Medium Scale Models

- Keeps calculations transparent
- Avoids “stranding” model-users
- Uses local export coefficients
- Adds in many reality checks
- Amenable to limited data means
- Can be easily updated to monitor progress during implementation

## Conclusions

- Some lakes can be modeled on the back of an envelope, others require expensive, sophisticated models, but most need something in the middle.
- TMDLs can be viewed as another regulatory requirement, but should be viewed as a tool to help set the direction of a management strategy.
- Medium-scale models help provide this direction when you are miles away from the target.  Precision is more crucial during implementation.

## Questions?

**A model is more than a pretty interface,**
**look closely at what’s inside**