A map service and web application where users can extract flood

statistics from a regional flood model, at-site flood statistics and annual

maximum flows from flow recorders used in the model development, flood

estimates based on rain intensity for use in the Rational Method. 

1. Modelled flood frequency estimates on river lines.

NZREACH NZ digital network 1 ID no.

River name where available Area km2 catchment area draining to the downstream end of this reach (square kilometres)q100_reach ratio of Q100 (1% aep flood) to mean annual flood

C18_MAF mean annual flood (cumecs)

C18_5-yr 5-yr (20% aep) flood (cumecs)

C18_10y 10-yr (10% aep) flood (cumecs)

C18_20y 20-yr (5% aep) flood (cumecs)

C18_50y 50-yr (2% aep) flood (cumecs)

C18_100y 100-yr (1% aep) flood (cumecs)

C18_1000y 1000-yr (0.1% aep) flood (cumecs)

HCse_MAF standard error of mean annual flood (cumecs)

HCse_5y standard error of 5-yr (20% aep) flood (cumecs)

HCse_10y standard error of 10-yr (10% aep) flood (cumecs)

HCse_20y standard error of 20-yr (5% aep) flood (cumecs)

HCse_50y standard error of 50-yr (2% aep) flood (cumecs)

HCse_100y standard error of 100-yr (1% aep) flood (cumecs)

HCse_1000y standard error of 1000-yr (0.1% aep) flood (cumecs)

Strm_Order Strahler stream order (1=headwater, two ones join to make an order 2, etc.)

2. At-site flood statistics at flow recorders used in the model development

Siteno NIWA reference number for flow recorder Name Flow recorder name generally 'river' at 'location'

NZTM_E NZTM easting

NZTM_N NZTM northing

Region Regional council or unitary authority territory

Operator Organisation that operates the flow recorder Funder Organisation that funds the flow recorder (can be more than one)Area_km2 catchment area draining to the flow recorder (square kilometers)

No_years Number of years in the annual flood series (allowing for years with missing data)

L1_mean Mean of the annual flood series (linear moment 1)L2 Linear moment 2 of the annual flood series (analogous to standard deviation)Lcv Linear CV of the annual flood series (L2/L1)

T3_Lskew Linear skew ratio of the annual flood series T4_Lkurt Linear kurtosis ratio of the annual flood series Gumb_u Gumbel distribution u of the annual flood series Gumb_alpha Gumbel distribution alpha of the annual flood series GEV_u Generalised Extreme Value u of the annual flood seriesGEV_alpha Generalised Extreme Value alpha of the annual flood series GEV_k Generalised Extreme Value k of the annual flood series GEV_z Hosking-Wallis normal standard variate to test significance of GEV-k (is the at-site distribution Gumbel or not?)Data 2.33y mean annual flood (2.33-yr assuming Gumbel, or 43% aep)

Data 5y 5-yr (20% aep) flood (cumecs)Data 10y 10-yr (10% aep) flood (cumecs)

Data 20y 20-yr (5% aep) flood (cumecs)Data 50y 50-yr (2% aep) flood (cumecs)

Data 100y 100-yr (1% aep) flood (cumecs)Data 250y 250-yr (0.4% aep) flood (cumecs)

Data 500y 500-yr (0.2% aep) flood (cumecs) Data 1000y 1000-yr (0.1% aep) flood (cumecs)

se_2.33y standard error of mean annual flood (%) se_5y standard error of 5-yr (20% aep) flood (%)

se_10y standard error of 10-yr (10% aep) flood (%)se_20y standard error of 20-yr (5% aep) flood (%)

se_50y standard error of 50-yr (2% aep) flood (%)

se_100y standard error of 100-yr (1% aep) flood (%)

se_250y standard error of 250-yr (0.4% aep) flood (%)

se_500y standard error of 500-yr (0.2% aep) flood (%)

se_1000y standard error of 1000-yr (0.1% aep) flood (%)

3. Return period estimates of the area-rain intensity values for small catchments.

Where results display '-1' the catchment is greater than 30 square

kilometres and no answer is available. Numbers need to be multiplied by

the Rational Method 'C' factor to give the required flood magnitude.

NZREACH NZ digital network 1 ID no.

AREA_km2 catchment area draining to the flow recorder (square kilometers)

QIA_5y 5-yr (20% aep) IA estimateQIA_10y 10-yr (10% aep)

IA estimate QIA_20y 20-yr (5% aep)

IA estimateQIA_50y 50-yr (2% aep)

IA estimateQIA_100y 100-yr (1% aep)

IA estimate QIA_1000y 1000-yr (0.1% aep)

IA estimate 4. Annual data values at flow recorders used in the model development.

Owner: NIWA_OpenData