ABSTRACT

Best management practice (BMP) strategies are used in rural and urban areasto reduce the impact of downstream water quantity and quality problems.The effectiveness of BMP facilities are evaluated using field data andcomputer tools. Field data are site specific and, in many cases, time and laborintensive. Many environmental and economic models require highly skilledand experience professionals. A more user friendly and easy to use tool basedon environmental (hydrology, flood routing, and pollutant removalmechanisms) and cost variables is needed to evaluate the effectiveness ofBMP/LID facilities.

BACKGROUND

This poster intends to show the development of a new tool (using VBAprogramming for Microsoft Excel) to evaluate and link rainfall-runoffgeneration and outflows from selected BMPs facilities.

To evaluate the effect of a BMP on peak attenuation it is necessary toestimate the variation of flows in time and space. The routing process usesmathematical expressions to calculate flow from a reservoir or a storagefacility once inflow, initial conditions, facility characteristics and operationalrules are known [1].

All hydrologic routing methods are founded on the equation of continuity,which may be expressed as:

(1)

The Storage Indication Method is recommended for reservoir routingcalculations and for detention facilities final design [2].This method is basedon the average rates of flows for some small increment of time during thehydrograph, producing the following approximation of the continuityequation

(2)

A reasonable estimate can often be made of O1 and S1, but the unknownsare S2 and O2. In order to step through time on the flow hydrograph, theequation may be reformulated as:

(3)

The use of the Storage-Indication Method requires reliable description ofthe following three items [3]:

An inflow runoff hydrograph.

Determination of the relationships between Stage-Storage, which can bedeveloped by successive calculations of storage vs. associated stages in thestorage facility.

Determination of the relationships between Discharge-Stage, it is basedon the association of the reservoir stage (head) and the resulting outflowfrom the storage facility.

The basic equation for sharp-crested and broad-crested weirs , the mosttypically used weirs [4], is:

(4)

In existing urbanized areas, BMPs canbe implemented to address a range ofwater quantity and water qualityconsiderations. For new urbandevelopment, BMPs should bedesigned and implemented so thatthe post-development peak dischargerate, volume and pollutant loadings toreceiving waters are the same as pre-development values (fig 1).

Fig 1. Impact of land use changes on hydrograph

OIdtds

−=

( ) ( )[ ] 1212122SSOOIIt

−=+−+=∆

( ) 22

11

1222 O

tSO

tSII +

∆=

−∆

++

23

LHCQ w=

METHODOLOGY

BMP

Mod

ule

Facility Dimensions Inflow Time Series Selection Control Structures

Flow Routing

Stage-Outflow-Storage routing (3) using weir or orifice equations (4)

Hydrograph

Hyd

rolo

gic

Calc

ulat

or V

ersi

on1.

2

Soil Characterization (land use, hydrologic soil group, and

size)

Site Information (drainage area, slope and length)

HydrographSanta Barbara Unit Hydrograph Method

base on Curve Number Method

Rainfall Data

Design Storm

EXAMPLE SETUP

A hydrograph example to develop the routing process was taken from Austin Moore Hydrologic Calculator Version 1.2 model . Figure 2 shows the input screen and example from this model.

Step 3: Rainfall Data• Begin in Step 1 by inputting project information. Select a STATE, then COUNTY to generate• In Step 2, input data relevant to the site including rainfall data, OR input your own data. site size, hydraulic length, and average slope.• In Step 3, select a State, then County to generate rainfall data, OR input user-defined data in the cells. County: Then select a design storm.• Click 'Proceed to Land Use' to input land use data.

Denotes a required input.Denotes an ouput.

Name:Date:Organization: 1 inch storm 1.0Project/Site: 1 3.6

2 4.2Step 2: Site Information 5 5.3

Size 5.00 acres 10 6.1 n/aL 263.30 ft 25 7.0 n/a

Slope 0.001 ft/ft 50 7.8 n/a100 8.6 n/a

Example

Step 1: Project Information Rainfall Return

Period (yr)

inches

24-hour Rainfall

Amount (in)

Select Design Storm

Austin Moore4/20/2010 8:26MSU

Instructions:

State:

Rainfall Distribution: Type II

Annual Precipitation: 55.96

Mississippi

Select a CountySelect a CountySelect a CountyOktibbeha

Fig 2. Inflow hydrograph calculation example

This example calculates the hydrograph for a site with the following descriptionLocation: Oktibbeha County, MS Area: 5 acres Length: 263.30 ftSlope: 0.001

Rainfall distribution: type II Rainfall return period: 5 yearsRainfall amount: 5.3 in

Input land use data and soil characteristics are shown in figure 3.

Hydrologic Soil group BPre-developed land use: Open Space, fair condition.

Post-developed land use: Urban Districts, commercial/business

The results obtained are:

A brief summary of all data used and results (fig 4) A hydrograph for both cases (pre and post development)

Fig 3. Land use example

Fig 4.Runoff results

Figure 6 depicts three hydrographs: pre-development, post-development, andpost-development with detention facility. It is apparent the runoff peakattenuation and translation of the hydrograph due the BMP structure

Fig 7. Hydrographs

The BMP module calculates the relations required(fig 6) by the storage indication method:

Elevation- StorageOutflow-StorageStorage Indication function

Fig 6. Storage-outflow function development example

RESULTS

Project InformationName:Date:Organization:Project/Site:

Control Structures

Orifice Diameter 3.00 (inches)Orifice Height 0.50 (ft)

Discharge Coeficient 0.61General Storage Design Procedure

Maximum Depth 5.00 ftBottom Width 30.00 ft Weir Crest Width 10.00 (ft)

Length 125.00 ft Weir Invert 0.50 (ft)Side Slope (H:V) 1.00 ft/ft Discharge Coefficient

Z(ft) Storage (ft3) Weir Crest Width 15.00 (ft)0 6.90E+06 Weir Invert 0.60 (ft)

0.5 7.72E+06 Discharge coefficient 3.001 8.58E+06

1.5 9.49E+062 1.04E+07

2.5 1.14E+07 Vertex angle (deg)3 1.24E+07 Weir Invert

3.5 1.35E+07 Discharge Coeficient4 1.46E+07

4.5 1.58E+075 1.70E+07

MSU

Germania Salazar4/16/2010 9:31

Orifice

Sharp-Crested Weir

Broad-Crested Weir

V-Notch

Availability Elevation Storage Relationship

The elevation-storage relationship known

The elevation-storage relationship unknown

Fig 5. Design of facility and control structures

In this example the storage values were computed by solving the broad-crested weir equation, assuming a constant discharge coefficient of 3.0,and weir length of 15 feet.

Facility designTrapezoidal channelDepth 5 ftWidth 30 ftLength of 125 ftSide slope 1 ft/ft

REFERENCES

1. Sturm, Terry W., “Open Channel Hydraulics.”McGraw-Hill Water Resources and Environmental Engineering Series, New York, February 2001.

2. Metropolitan Government of Nashville and Davidson County (2000). StormwaterManagement Manual.

3. Ponce, V. M. (1989) “Engineering Hydrology. ” Prentice Hall. Upper Saddle River, New Jersey.

4. North Carolina Department of environment and Natural resources (NCDENR). “Stormwater Best Management Practices Manual.” (2007)

5. Moore, A. “Hydrologic Calculator Version 1.2.” (2010). MSU Landscape Architecture Master Student.

Germania Salazar1, Wayne Wilkerson2, James L. Martin1, William H. McAnally1, Jairo Diaz1,Austin Moore2.

1 Department of Civil & Environmental Engineering, Mississippi State University, 2 Department of Landscape Architecture, Mississippi State University.

DEVELOPING A USER-FRIENDLY TOOL FOR BMP/ LID MODELING USING VBA PROGRAMMING

ACKNOWLEDGMENT

This project is funded by the Northern Gulf Institute (NGI) project 09-NGI-01,Developing a Tool for Assessing Cost Effective Best Management Practices forResilient Communities.

FUTURE RESEARCH

Model updates: The model will take into account other hydrologic abstractionslike infiltration. Also, the tool will include screens for BMP cost and effectiveness.In addition we are planning test this tool by collecting data in a vegetated swalelocated in MSU South Farm.

The post-developed hydrograph is the inflow into the BMP facility.

The following flow chart shows the methods used in this project.

Where:S is storage (L3), t time (T), dS/dt the time rate of change in storage, I is the inflow rate, O the outflow rate (L3/T)

Where: Δt is the time difference and the subscripts 1 and 2 refer to the end and the beginning, respectively, of the time period Δt.

Where: Q is the water flow rate, c discharge coefficient, L width of the weir, H height of the water over the weir.